Advances in Organometallic Chemistry, Volume 46

Contributors PENELOPE J. BROTHERS (223), Department of Chemistry. The University of Auckland, Auckland, New Zealand BARRETT EICHLER ( I ), Department ofChemistry, University ofcalifornia-Davis. Davis, California 956 I5 MARK G. HUMPHREY (47) Department of Chemistry, Australian National University. Canberra, ACT 0200 Australia LALEH JAFARPOUR (ISI), Department of Chemistry. University of New Orleans, New Orleans, Louisiana 70 148-2920 IL NAM JUNG ( 145). Organosilicon Chemistry Laboratory. Korea Institute of Science and Technology, Seoul 130-650, Korea NIGEL T. LUCAS (47), Department of Chemistry. Australian National University. Canberra, ACT 0200 Australia STEVEN P. NOLAN (181) Department of Chemistry, University of New Orleans. New Orleans. Louisiana 70148-2920 SUSAN M. WATERMAN (47). Department of Chemistry, Australian National University. Canberra ACT 0200 Australia ROBERT WEST (I), Department of Chemistry, University of Wisconsin. Madison, Wisconsin 53706-1396 BOK RYUL YOO ( l45), Organosilicon Chemistry Laboratory. Korea Institute of Science and Technology. Seoul 130-650, Korea

vii

ADVANCES

IN ORGANOMETALLIC

CHEMISTRY,

VOL. 46

Chemistry of G roup 14 Heteroallenes BARRETT

EICHLER

Department of Chemfsfry University of California-Davis Davis, California 95616

ROBERT WEST Department of Chemistry University of Wisconsin Madison, Wisconsin 53706 I. II. III.

IV.

V.

Introduction Bonding Theory Synthesis and Reactions A. Transient I-Silaallenea B. Transient I-Silaketcnes. C. Stable Heteroallenes Physical Properties A. X-ray Structure Determination. B. NMR Spectroscopy Future Prospects References.

,........

.............. .............. .............. .............. ..............

I 2 5 5 14 I/ 34 34 40 43 43

I INTRODUCTION

An allene (or 1,2-propadiene) is a moiety with two cumulated double bonds between three atoms (R2C=C=CR2). The central atom of the allene is therefore sp-hybridized. The r-bond of one double bond is orthogonal to the other and this unusual n-bonding arrangement can lead to unique electronic effects (Fig. I). This also results in steric properties at the ends of the allene by forcing the substituents to also be orthogonal to each other. This review will focus on allenes which have at least one carbon atom replaced by a heavier group I4 atom, commonly referred to as a heteroallene. Group I4 heteroallenes have appeared in the literature over the last 20 years, and stable examples of this moiety have been synthesized since 1992. Heteroallenes that do not have a group 14 heteroatom will not be discussed, although it is useful to consider phosphaallenes, which have been reviewed by Regitz in 1990.’ To date, heteroallenes with the heteroatom at the end of the allene, the one position, have been easier to synthesize because of their thermodynamic stability compared to those with the heteroatom as the middle atom, the two position.

1 All rights

Copyright c’ 2001 by Academic Press. of reproduction in any form reserved. 006%3055/01 $35.00

2

BARRETT EICHLER AND ROBERT WEST

II

BONDING

THEORY

Heteroallene structures can be regarded as depending on the extent ofcontribution from each of two bonding arrangements (Fig. 2). Bonding Model A depicts both the heteroatom and the carbon atom in the triplet state, forming one a-bond and one r-bond to make a formal double bond. Lappert et 01.‘~’first postulated bonding Model B, and illustrated bonding between the heteroatom and the carbon atom in singlet states that “may be described as a ‘double’ n-donor-acceptor interaction.” according to Griitzmacher et ~l.‘~ Differences between these two models

Model

\. /

A

M.

1

./

.(‘=c‘

h \

\ /

M=c‘=(‘

/ \

Chemistry of Group 14 Heteroallenes TABLE RELATIVE ENEKGIES OF C2HISi H$.Y=Si=CH:

H$i=C=CHJ

I ISOMEKS (kcal IIIOHjSi-C=CH

) Ref.

leads to obvious differences in geometry in order to maximize orbital overlap. Model A should lead to a linear allene backbone and Model B should produce a structure bent at the central carbon, as well as pyramidalization at the heteroatom. The key issue in determining which model applies to a particular system is the singlet-triplet energy difference’ for both atoms involved in bonding. Typically, the triplet state is favored only for carbon, whereas silicon, germanium, tin, and lead favor the singlet state. The filled orbitals of the heavier atoms are progressively richer in s-character and therefore the singlet state becomes more energetically favorable as one moves down the periodic table. Thus, the pure carbon allene bonding is dominated by the triplet contribution, and so the Ci=CI=C3 bond angle should be I80 ‘. In the heteroallenes, the bond angle may deviate from I80 ‘, and the bending is predicted to increase as the size of the heteroatom increases. The empirical results. which agree very well with this view, will be discussed later. Several groups have reported ab initio calculations of CzH$Si isomers’m7,“‘: some of the results are listed in Table I. The most stable structure is ethynylsilane. Relative to this molecule, I silapropadiene is less stable by about 25-30 kcal mop’ (Ref. 12(f) places the energy of the parent silaallene ca. 55 kcal mall’ above ethynylsilane) and 2-silapropadiene is even more unstable, lying ca. 50 kcal mall’ above ethynylsilane. This is consistent with the fact that I-heteroallenes have been isolated, but 2-heteroallenes are still unknown. A recent calculation’” of the relative energies of CH$iO isomers shows that a bent silylene-carbon monoxide adduct (lone pair donation from carbon to empty p-orbital on silicon) is the most stable. and the planar/linear H$i=C==O isomer (strong double bond between silicon and carbon) lies 16.6 kcal mol’ higher in energy (Fig. 3). Earlier energy calculations of (CH&SiCO provide contrasting results depending on the methods used-MNDO/AM I calculations predict the minimum energy structure is the planar/linear silaketene, but ah initio calculations favor the pyramidal silylene-CO adduct. Although no stable heteroketenes have been synthesized to date, structural, spectroscopic, and reactivity data from related heteroketenimines (Sects. IIIC3 and IV) also suggest that the silylene-CO adduct is more stable.

4

BARRETT EICHLER AND ROBERT WES-I

slylene-carbon

monoxide

lineal-/planar silaketene

adduct

FI(~. 3.

It is instructive to examine the atomic charges predicted for various propadienes. The normal polarization of the Si=C double bond in silenes is calculated to be strongly polarized, Si+-C-, with large net charges of fO.46 on silicon and -0.67 on carbon (Table II). In allene itself, the C=C bonds are also substantially polarized, with net negative charge on the outer two carbon atoms6 In 2-silaallenes. the net charges on silicon and carbon are predicted to be quite similar to those in silenes, but in I-silaallenes, the net charges on all three atoms are greatly reduced. The normal allene polarization evidently cancels out much of the Si=C polarization. Thus, I -silaallenes are far less polar than silenes and 2-silallenes, and so may be less reactive toward polar reagents. Calculations have been reported only for silaketenes (see below), but similar trends are likely for the other group I4 heteroallenes. Apeloig and co-workers have pointed out that decreased polarity of the Si=C double bond is also calculated for silenes with oxygen substitution, i.e.. H2Si=CH(OSiH3).” In this case. the reduced net charges are due to resonance electron donation by oxygen. The calculations are in accord with the greater Si=C bond length. increased ‘“Si shielding. and decreased ‘jC shielding found in Coxygen-substituted silenes. compared with ailenes lacking oxygen substituents. Atomic charges were calculated ” for parent silaketene, HlSiCO, using generalized atomic polar tensor (GAPT) population analysis. Two geometries were investigated-the “doubly bonded” planar and the “silylene-CO adduct” bent. The most important point relative to the examination of heteroallenes is that the planar structure has a significantly more negative charge on silicon (-0.05, C = + I .27) than does the bent structure (f0.32. C = +0.X I ). Based on the charge calculations for silaallenes, a slight negative charge on silicon seems unlikely, making the bent structure a better model than the planar structure.

TABLE

II

rs,=c.pn’

Si. Chg.

Ref.

171.x 170.2 170. I

+o.lh +o 17 fO.50

9 IO IO

Chemistry

of Group 14 Heteroallenes

SYNTHESIS

AND REACTIONS

A. Transient I-Silaallenes

Extensive studies of the photolysis and thermolysis of alkynylsilanes and silacyclopropenes were carried out by Kumada and Ishikawa, beginning in 1977. The first report of a group 14 heteroallene in the literature was the proposal by this group of a transient I -silaallene as a product of the photolysis of a I alkynyldisilane (la)“” (Scheme I). When this precursor was irradiated in the presence of methanol, a I .3-silyl migration occurred. The major products (400/r) were methoxysilaethenes. whose existence can be explained as being methanol adducts of I -silacyclopropene (2). Two additional methoxysilanes were isolated in a combined yield of 2 I YCand were rationalized as methanol trapping products of the intermediate silaallene 3. A similar photolysis of la in the presence of acetone produced the transient acetone adduct of the I -silaallene, a 2-silaoxetane,

PhC-CSiMqSiMcj

hv

-

A Ph

MC2 Si -

t SiMci

2

I

PhC=CSiMe;

MeOH

(PTMSA)

PI1

SiMe,

PI1 +

MeOMqSi

H

II

Ph

SiMqOMe

Ph

H

+ MeiSi

II %HhhlE

MqSi i

SiMezOMc

6

BARRETT EICHLER AND ROBERT WE.3

Mc;Si

3

MqC=O

\

( MezSiO),, % ‘HI:Mb

2.

which decomposed to an allene (4-5s isolated yield) and a siloxane (Scheme 2). This type of decomposition has been seen with other 2-silaoxetanes made from the ketone cycloadducts of silenes.13 It was proposed that photolysis of both la and 2 can eliminate :SiMez and phenyltrimethylsi1ylacetylene (PTMSA). Although this silylene elimination was not observed for the reaction in Scheme I, PTMSA was isolated in 5% yield in another reaction using methanol, and in 10% yield from the acetone trapping reaction in Scheme 2. Further studies’2h-” spanning nearly I5 years suggested that photolysis of other alkynylpolysilanes can, but do not necessarily, form I-silaallenes. In the paperlzh following the original communication, six I -alkynylpolysilanes were irradiated in the presence of methanol, but only four of the six (Sa-c, e) gave methanol adducts of I-silaallenes [~--EC). ( I )I. There is no clear-cut substituent pattern leading to I silaallenc production, but it seems that those precursors having more phenyl groups lead to higher yields of I -silaallene trapping products (cis + trans yields: 5a = l6%, 5b = 34%. 5c = 44%, 5e = 28%). The alkynylpolysilanes Sa-c and e were also irradiated from 3 to 9 h in the absence of methanol followed by immediate methanolysis of the photolysis products. None of the methanol adducts of I-silaallenes was found from these experiments, indicating that the I silaallenes. if formed, survived for only a very short time in solution. R’

II

hv

t+C‘ZC’SiR’R2R’

(a) R ’

R’ = MC. R’ = SIMCJ’II

(b) R’

Me. R’ = Ph. R’ = SiMq

(c) R’

R’=

(cl) R’ = R’= (c) R’

Ph. R’

SiMc,

Me. R’ = SiMc2S~Mc;

Me. R’

(1) R’ = K’

R’=

>=(

)

R’ = SIMC; SIMC:

II

cis-6

+

MeOH

5

S,R’K?OMC

I<’

II

II

SIR’R’OM~

mm-6

(I)

Chemistry of Group 14 Heteroallenes

MelSi

I

(MejSi)$J=C’=SiMesl 9

I

I

1 MeOH

J

SiMqOMe (MqSi)2C=(.: ti

10 SCHEMt:

3.

In another study,“’ Kumada and Ishikawa proposed that the stable 1-silacyclopropene 7, when irradiated in the presence of methanol, equilibrated with 1-alkynylpolysilane 8 and produced the methanol adduct (10) of the 1-silaallene 9 in 36% yield (Scheme 3). From previous studies using ultraviolet radiation as the photon source, it was shown that 8 was the most likely precursor to I-silaallene 9. Compound 7 was never indicated as a direct source of 9. From the observation that 8 is stable to visible light, whereas 7 is not, the authors inferred that the silaallene can be created from both 7 and 8. When 7 was irradiated with UV light for IO h, 7 and 8 were found in a constant 2/3 ratio irrespective of the time of irradiation, showing that 7 and 8 were equilibrating with each other. Irradiation of 7 with UV light in the presence of methanol gave methanol adduct (10) of I -silaallene 9 in 32% yield. But when a Pyrex filter (allowing only visible light to reach 7) was included in the photolysis with methanol present, compounds 8 and 10 were produced in 60 and 16% yields, respectively, clearly indicating that 7 . was converting to 9 when photolyzed. Experiments reported in 1982’Id by the same group provided the first example of heteroallene dimerization. In this work, head-to-head dimerization of I silaallenes Ila-c (Scheme 4) was observed, forming l,2-disilacyclobutanes 12a-c with two exocyclic double bonds.

8

BARRETT EICHLER AND ROBERT WEST

hv MelSiC-CSIArlSiMq

(MeqSI),C‘=(‘=SiAr:

___f

I

I

Ila-c

(a) Ar = wtolyl

(yield

= 20%~)

(b) Ar =/I-tolyl

(yield

= 21%)

(c) Ar = o-tolyl

(yield

= 2%‘)

*

m-adiatcd

in the prescncc

his-trimethylsilylacetylene improve

(Me$i)&‘N

//(SiMe?)> C-C’ I ArzSi-SiAr,

of

I

to

yteld

12a-c

When alkynyldisilanes 13a and b were photolyzedizg in the presence of freshly generated dimesitylsilylene (Mes?Si:), the silylene added to the Si=C double bond of I -silaallenes 14a and b to form disilacyclopropanes 15a and b (Scheme 5). Even without the independently generated silylene. photolysis of 13b produced 15b in 8% yield, but compound 13a gave only traces of Ea. In the case of 15b, the dimesitylsilylene most likely originated from silacyclopropene 16.

RCE-CSiMqSiMq

hv

h

R \ Mc;Si

13a,b

C=C‘=SIMes2

/

14a,b

’

[ :SiMw] hv

MCSz Si

R

A

[ :SiMesl]

t

SiMq

RCCSiMel

16a,b

1 i

(a) R

SlMc

(b)

Ph

R

SiMe,

R \

c

3’

Chemistry

of Group 14 Heteroallenes

PhCGCSiR’R’SiMe

1

1

(a) R,=R2= Me (b) RI-R,= SiMe3 (c) RI= SiMq, Rx: Mes

180-200°C I O-20 h, Ni cat.

PhC=<‘SIMe? I I LlNi-SiR’R’

17 -

- NiLz

NiLz PTMS ‘A

x2

I R’R? PhC-CPh II \ Me;SIC,Ci,CSiMe;

Ph

,, Si, _

.,SiMe3

Mc3Si>~c\Sl/c=(\Yh

klR2

R’R’

20

21

- NIL-,

Me2

23

PTMSA

Me:

24

SCHEME 6.

The Kumada/Ishikawa group also investigated thermolytic reactions ofalkynylpolysilanes and silacyclopropenes in the presence of nickel catalysts and implicated a I-silaallene-nickel complex as an intermediate in the reaction pathway to the observed products.“h-k When alkynylpolysilanes la-c (Schemes 6 and 7) were heated to 1SO-2Oo’C for 20 h in the presence of a catalytic amount of NiCI,(PEt& (la,b) or Ni(PEt3)d (lc) and two equivalents of PTMSA, products

IO

BARRETT EICHLER AND ROBERT WEST

I

R’=R’-

-NiLI

SiMq

PTMSA I

Ph

1 PhC=CSiMel I \ ,Me MqSi ’ Ni %iFvlt 1~2

MelSib--C

I ‘C-SiR’R’

‘1 I

I I PhC‘=CSiMej

25 27 - NiLl

PTMSA

;“z MejSiC ’

‘CPh

II

IICSiMei

Ph<

‘Si.( Me’

‘SiMeJ

26

were observed.“h Intermediates 17 (a nickelsilacyclobutene) and 18 and 19 (two isomeric I-silaallene-nickel complexes) were proposed to be in equilibrium with each other and were formed initially by a 1,3-trimethylsilyl shift. Intermediate 17a added PTMSA (Scheme 6) with loss of NIL? to form silole 20a (32%), whereas intermediate 18a simply underwent head-to-tail dimerization (-NiL2, IS%). Intermediate 19a performed an unusual rearrangement where the nickel moves a -SiMe* fragment from a -SiMe3 group to the cr-carbon, replacing the -SiMe? fragment with the remaining methyl group, forming intermediate 22a. This then added PTMSA to give a perfectly statistical distribution of isomers 23a (23%) and 24a (23%). The greater steric bulk of lb (two SiMe? groups) over that 2130

11

Chemistry of Group 14 Heteroallenes 2la (74%)

/“...

20 h cat. C12(PEt?)~Ni-PhC-CPh

PhC-CSiSiMqMeJ

cat.CI~(PEtl)~Ni-Me$iSiMe~H 200°C.2” h/.

Ia

MQ Ph\-

kCSi ’ ‘c=c’ Me;Si ’ ‘Si MC2

SiMe; ‘Ph

2la (28%),20a (3%). 23a + 24a (5%~)

2la (78%)

of la (two Me groups) caused the alkynylpolysilane to follow a completely different mechanistic pathway (Scheme 7). Compound lb did not produce any of the same compounds as la, instead forming 26 (58%) and 27a (19%). Compound 26 presumably formed via intermediate 17b, which rearranged in a manner similar to the formation of intermediate 22, and then added PTMSA. Compound 27b is the adduct of PTMSA with 1-silaallene intermediate 18b. Thermolysis of la with various nickel catalysts gave some surprising results (Scheme 8).lzh Possibly the most unexpected finding was that the thermolysis of la with NiClz(PEt& in the absence of PTMSA left la unchanged, but when it was heated with a catalytic amount of NiCl,(PEt&PhCCSiMe;, dimerization product 21a (28%) and PTMSA adducts 20a (3%) and 23 + 24a (5%) were obtained. Again in the absence of PTMSA, heating la with NiC17(PEt3)2-PhCCPh gave 21a (74%) and with NiCl2 (PEt&-Me$iSiMe2H also gave 21a (78%). To see if silacyclobutenes (28) would react in the same manner as the alkynylpolysilanes (1) and respond similarly to steric differences, compounds 28a and b were heated in the presence of NiCIz(PEt& and PTMSA (Scheme 9).“’ Cornpound 28a gave silole 20a in 94% yield, “j but the only isolable products from the thermolysis of 28b were 26 (51%) and 27b (36%). The products from the thermolysis of silacyclopropene 28b were very similar to that for alkynylsilane lb, but for some reason there were many fewer products for the thermolysis of 28a than for alkynylsilane la. These results suggest that the more sterically hindered lb

12

BARRETT EICHLER AND ROBERT WEST R’ ‘&/

R’

200°C. 20 h

w cat. NiCIz(PEt3)2

I\

PhC’=C‘SiMq

20a(94%)

28a 135°C. 15 I1 28b

L-

26(51%)

cat. NiCl2(PEt~)~ SC‘HI-.hlli

+

27b(36%)

9.

and 28b prefer the I -silaallene intermediate 18b, whereas the smaller precursors la and 28a prefer the nickelsilacyclobutene intermediate 17a, although electronic differences cannot be ruled out as important factors. To further illustrate the effect of steric hindrance, a bulky mesityl group was added to the alkynylpolysilane (lc) (Eq. (2)). “’ When lc was heated in the presence of Ni(PEt& and PTMSA, compounds 27c (77%) and 2Y (I I%-a compound similar to 26) were obtained, which is a product distribution similar to that of bulky lb.

;‘1 195°C 20 h IC

Ni(PEt3)4, PTMSA

MelSiC ’

-

27c(77%)

+

‘CPh

II

II

Ph(

C’Mc

‘Si.( MciSi

/

\

(2)

Mcs

29

Numerous other studies” by Ishikawa and co-workers, with or without nickel catalysts, have reinforced the importance of I -silaallenes and nickel-complexed I-silaallenes as intermediates in the pathways of the photolyses and thermolyses of alkynylsilanes. Barton and co-workersI performed flash vacuum pyrolysis (FVP) on trimethylsilylvinylmethylchlorosilane (30), resulting in the production of trimethylchlorosilane (30%), trimethylvinylsilane (I 1.5%) and most interestingly, ethynylmethylsilane (34, I I .9%). A proposed mechanism for the synthesis of 34 (Scheme IO) begins with the loss of trimethylchlorosilane to form silylene 31, which can rearrange either to silaallene 32 or to silirene 33, both of which can lead to the isolated ethynylsilane. Maier et al.’ studied the FVP of another vinylsilane, 35 (Scheme II). They proposed that, instead of leading directly to the observed products, silaallene 37

Chemistry

800°C

4 x 10m4torr 1

13

of Group 14 Heteroallenes

H

\

1 Si=(.=CI12 / fl MC 32

\ /

l12MeSi---C’ECfI

%‘HfihlE

10

was in an equilibrium process with silylene 36 and that the silylene directly made silacyclopropene 38, which photolyzed to ethynylsilane 39.

The early photolysis studies of Kumada and Ishikawa have been greatly augmented by recent investigations of the laser flash photolyses by Leigh and his students, in which the silapropadienes have been characterized spectroscopically.‘h.‘7 Thus, the flash photolysis of 40 using a KrF excimer laser produced transient compounds 41 and 42, along with a non-decaying species, 43” (Scheme 13). These products were identified on the basis of their UV absorption spectra and reactivity. Silaallene 41 is a minor (-15%) photoproduct, but could be identified because it is relatively long lived compared with silylene 42, and has rather strong electronic absorption bands at 275 and 325 nm. Compound 41 reacted with MeOH, r-BuOH, HOAc, acetone, and 02; absolute rate constants were obtained for these reactions by quenching studies. Also investigated by the group was the flash photolysis of la, leading to 2 and 3, the transient products postulated earlier by Kumada and Ishikawa, as well as dimethylsilylene and the stable product PTMSA.” Quenching reactions and UV spectroscopy again identified the products. Silaallene 3 reacts

14

BARRETT EICHLER AND ROBERT W E S T

Me;SiH$i

35

650°C

IO-’ mbar

MqSiH 1

39

38 SC‘HEMI~ I I.

more rapidly with quenching agents than does 41, by factors of 20 to 1000. The difference is suggested to result from a combination of steric effects and hyperconjugative stabilization of the Si=C bond in 41 by the trimethylsilyl substituent.

B. Transient

I-Silaketenes

Using CO-saturated hydrocarbon matrices, Pearsall and Westlx photolyaed silylene precursors at 77 K and monitored CO coordination to the silylenes by UV-vis spectroscopy (Scheme 13). Bis(trimethylsilyl)silanes 44a-c or Si(,Met:! were irradiated at 254 nm to create silylenes 45a-d, which reacted with CO, causing new peaks to ca. 290 and 350 nm, which were attributed to complex 46a-d, a resonance structure of silaketene 47a-d. Silylene adducts form fairly weak bonds. as seen by warming of the matrices. In the case of silylene adducts where one R = Mes, the CO dissociates and the corresponding disilene 48a-c peaks in the UV-vis spectra observed upon warming (Rl = Me most likely produced silane rings SiiMeh. etc.).

Chemistry of Group 14 Heteroallenes

15

Me$C~CSiMqSiMe3 40 hv

hexane McOH

Me$ Me$i

\

Me C=C=Si’

/ 41

+

\

MqSi:

+

Mc&CEC’SiMe$3iMc~ 43

42

Me

MTSIASiMe ?

3

46%

McOtl

MeOH

MeOH

Me,Sl

SiMezOMe >--<

t

+

t MCjSI

MezSi H

/ \

tl

H Me&

OMe

SiMcrOMe P<

SiMei 23%

12% %‘Hf:ME

12

A separate study of the interaction of :SiMez with CO in an argon matrix (Scheme 14) was carried out by Arrington et al. ” Dodecamethylcyclohexasilane or dimethyldiazidosilane were irradiated in the presence of CO at I5 K and produced a silylene-CO adduct. This species was detected by infrared (CO stretch = I962 cm-‘) and UV-vis (peak at 342 nm) spectroscopies and the intensities of the peaks increased upon warming, indicating that more of 46d was being formed at higher temperatures owing to the increased mobility of the reactants in the matrix. Maier and co-workersx condensed formaldehyde and elemental silicon at 12 K in an argon matrix and photolyzed the mixture to form silaketene HzSiCO, which is similar in structure to the silylene-CO adduct mentioned above. The reactants first form siloxiranylidene 49 (which equilibrates with an unknown species postulated as the planar/linear silaketene 50 when exposed to 3 I3-nm-wavelength light) and then forms complex 51 when photolyzed at 366 nm (Scheme 1.5). This species could also be formed by photolyzing diazidosilane 52 in the presence of CO, and complex 51 equilibrates with Sic0 (53) and Hz. The CO infrared shift for this bent structure was calculated at 2129 cm-‘, which is shifted -8Ocm-’ from the calculated value of free CO, at 22 10 cm- ‘. The experimentally observed value was reported at 2038-2047 cm-’ at I2 K.

0:

-

R$G=C’=O 47a-d A

i (a) (b) (c) (d)

R= R= R= R=

Mesz Ma; OPh-2,6-iPr Ma; tBu MeI

48a-c

(SiMe),,

46d

.. si. .

Ar +

HX==O

I2

hv (3 13 nm)

i-i

. K

-

/\

hv (435

HzC’-0

HzSi=(‘=O

:’

nm) SO

49

I

hv (366

llnl)

‘lV (2’)o ““‘J-

H2Sl(N&

hvl313

:s1=(‘=0

nm) 53

52 SC‘HthlF

15

Chemistry

McO

17

of Group 14 Heteroallenes

I-PI

I-Pr

Br

; ,D

OMc

54

I

I

56

OMc

55 hle?

2.4.6.rri-t-butylphenyl,

I -Ad

= I -adamantyl SCHINE

16.

C. Stable Heteroallenes

The first stable silaallene, 56, was synthesized in 1993”‘.-I2 by the intramolecular attack of an organolithium reagent at the B-carbon of a fluoroalkynylsilane (Scheme 16). Addition of two equivalents of t-butyllithium in toluene at 0 ‘C to compound 54 gave intermediate 55. The cY-lithiofluorosilane then eliminated lithium fluoride at room temperature to form the 1-silaallene 56, which was so sterically hindered that it did not react with ethanol even at reflux temperatures. 1-Silaallene 56 was the first, and so far the only, multiply bonded silicon species to be unreactive toward air and water. The X-ray crystal structure and NMR spectra of 56 is discussed in Sect. IVA. In 1997,2’ the intermolecular addition of organolithium reagents to fluoroalkynylsilanes was used to synthesize three novel, stable I-silaallenes. In this

18

BARRETT EICHLER AND ROBERT W E S T

R”Li

7’

R-Sj-C--(‘Pi1 F 57a,b,c

1

A, -LiF

(a) R, R’= Tip, R”= t-Bu (b) R- Mes*. R’, R”= t-Bu (c) R= Mm*. R’=t-Bu. R”= Pb

Ph R’//,,,

SizxzCzC’ \

R’

R”

59

Tip = 2,4,6-tri-isopropylphenyl Mes*= 2,4,6-tri-/-butylphenyl

salt-elimination approach, one equivalent of the organolithium reagent is added to a solution of a sterically hindered (to prevent attack at silicon) fluoroalkynylsilane 57. The organic part of the organolithium compound adds to the B-carbon of the alkyne and the lithium is transferred to the a-carbon, forming cr-lithiosilane 58 (Scheme 17). Compound 58a was stable at 0°C in solution and was trapped by methanol, forming the cr-hydrovinylsilane 60a (Eq. (3)). The TMEDA complex of compound 58a was studied by X-ray crystallography, clearly showing that this intermediate is present in solution prior to the formation of 1-silaallene 59. These intermediates were not detected for I-silaallenes 59b or 59~. Further warming (25 ‘C for 2 h for 59a; 0 C for I h for 59b; 25’ C for 3 days for 59~) led to elimination of lithium fluoride, providing I-silaallenes 59a-c. PI1

58a

MeOH

t-Bu

t F

H

(3)

60a

I-Silaallene 59a decomposes to silacyclobutane 61 (Eq. (4)) upon heating to 135°C in solution. This sole decomposition product was created from the insertion of the Si=C double bond of the silaallene into one of the ovtho tertiary carbon isopropyl C-H bonds, which are preferred (or more acidic) over the primary carbon methyl C-H bonds on the isopropyl groups, which would form a less strained five-membered ring.

Chemistry

19

of Group 14 Heteroallenes

.

i-Pr l

135°C *w

i-Pr

I

,i;:!

‘Tip

59a

(4) %-Ph 1 r-Bu

61

Only one type of reaction occurred for I-silaallenes 59b and 59~ (Eq. (5)). The greater steric bulk of the substituents on silicon led to a similar insertion of the Si=C double bond into a C-H bond on one of the ortho r-butyl groups on the Mes* group, forming the five-membered ring 62. In this reaction, there is no longer a tertiary C-H bond to insert into, giving only one option for insertion into a C-H bond, that of rearrangement to the silacyclopentane. The insertion occurred in three separate pathways for 59b. The first was observed when 59b was heated to 90~ C overnight. The second method for synthesis of 62b was to stir 59b with excess ethanol at room temperature for several hours. The same rearrangement occurred upon mixing at -78°C when a catalytic amount of acid in excess ethanol was added to 59b. Excess deuterated ethanol and 5 mol% D#Od added to 59b incorporated a deuterium atom in the cu-vinylic position (>95’%, 63), suggesting initial protonation (deuteration) at the I-silaallene central carbon (Scheme l8), thereby creating a reactive silicenium ion, which inserts into an ortho r-butyl C-H bond, liberating H+ and making 64. I -Silaallene 59~ is less sterically hindered and forms 62c under mild conditions of excess ethanol at room temperature in only a few seconds.

A, EtOH or EtOH(H+)

59b,c

R (b) R= t-Bu (c) R= Ph

62b,c

(5)

Compound 59a underwent intermolecular reactions characteristic of silenes (Scheme 19). Water added instantly across the Si=C double bond of the I -silaallene is expected to give vinylhydroxysilane 65 in 7 I % yield, and methanol was added

BARRETT EICHLER AND ROBERT W E S T

20

EtOD(D’)

59b

_

-Ph

Ph

Ph

’ t-Bu

HO

H

65 Ph t-Bu

Me0

11

SCHtMvlr:

” I’).

Chemistry

t-Bu-Si--C‘eC

21

of Group 14 Heteroallenes

2 t-BuLi

t-Bu-Si--C‘=C

25°C

t-Bu

- LiF

/ IO

SCHEME

20.

to provide vinylmethoxysilane 66 in 78% yield. Benzophenone also reacted with 59a to give a mixture of E- and Z-isomers of 1,2-oxasiletane 67 in 22% isolated yield. Two more novel silaallenes were reported in 199.5” and 1999”. I-Silaallene 70”,” was synthesized (Scheme 20) from alkynylfluorosilane 68 and two equivalents of r-butyllithium to give intermediate 69, which eliminates lithium fluoride upon warming to room temperature for 2 to 6 h yielding bright yellow silaallene 70. Compound 70 is stable in rehuxing neutral or slightly basic ethanol for 3 days, but undergoes a rearrangement (Scheme 2 1) similar to that of silaallenes 59b and 59~ when submitted to slightly acidic conditions in refluxing ethanol, giving 71. Silaallene 70 also photolyzes to insert the Si=C double bond into the C-H bond of the nearest methyl group on the fluorenyl moiety to form the strained silane 72. Silaallene 73” was synthesized in an manner analogous to that of 70. Compound 73 was stable at room temperature over I month, but in the presence of any protic source (i.e., water, methanol), it underwent a rearrangement different than that observed for 70, inserting into a methyl C-H bond (74) on the octamethylfluorenyl moiety rather than into one of the groups on silicon (Eq. (6)). It is believed that the favored mode of rearrangement for these groups is that of silaallene 73, but 70

22

BARRETT EICHLER AND ROBERT WES-I

is too sterically hindered to do so, and therefore the Si=C double bond is near enough only to the group on silicon to react to form 71.

-

H‘

(6)

West et al. have recently described the synthesisZJ and reaction? of a Igermaallene. Germaallene 76 (Eq. (7)) is analogous to silaallene 59a and is synthesized by intermolecular addition of t-butyllithium to precursor 75, followed by salt elimination at -78°C. This germaallene is not stable above 0°C in solution. but remains intact until heated above 90°C in the solid state. In either case, the

23

Chemistry of Group 14 Heteroallenes

germaallene performs an insertion of the Ge=C double bond into a C-H bond on an ortho isopropyl group, forming four-(77) and five-membered (78) rings (Eq. (8)) in a ratio of approximately 3:2, depending on which C-H bond is inserted into. Compound 76 also added external reagents such as water and alcohols across the Ge=C double bond to make compounds 79a-c (Eq. (9)). Benzophenone was too large to add to the germaallene at O”C, but benzaldehyde added readily to provide oxagermetane 80 (Scheme 22). Germaallene 76 also reacts with acetone to give the unexpected trapping product 79a. PI1

t-BuLi Tip$;e--CC-Ph

v

/

Tip+=C’=C -78°C’

I F

\

(7) t-Bu

76

75

0°C (solution) e > 90”~ (solid) 76

i-Pr

+

i-Pr-

t-h 77 (60%)

t-Bu

I

I ROH 76

’

(a) R= H (b)R=Me (c) R= Et

Tip

//c-ph

;e--C I OR

I H

79

(9)

Another germaallene was also reported in 1998 by Okazaki rt a/.rc,h Initially, the report of a germaallene trap with chalcogens, alkylidenetelluragermirane 86a, appeared in I 997.26”The germylene precursor 82 is made in situ from dichlorogermane 81 and two equivalents of lithium naphthalenide (Scheme 23). The addition

24

BARRETT

Tbt(Mes)GeClz 81

-

2 LiNp -2

Mea \(je=(‘=C Tht

/

EICHLER

AND

ROBERT

WEST

[ Tbt( Mes)Ge 1 82

LiCl

Mes *

:I

t 82

rht-(ie--C’=(’ I I C‘I C’I

- 81

’

85

8

:I

84

(a) E=Tc (h) E- S (c) E- SC

86 Tht= 2,4,h-tris[his(trimcthyls~lyl)methyl]phenyl WHEMF~

21.

Chemistry of dichloromethylenefluorene leads rinated

by the addition

dichlorogermane from

83 and tributylphosphine

first to compound

84, which

(MC) (Eq. amide

from

elemental

Ma sulfur Ma

in order lo reversibly melhod

was reactud abstract

with

88. Germaallene

85 also

to that of gertnaallenc

76 to make

temperature

(50%

for 3 days

This re;tction

ways.“‘”

excess

phosphorus

by addition 85 reacted

87 and with mcsitonilrile

four-membered

tri-

atom away from the germaallene.

dehalogeilation

underwent

complete)

also

In the first method

hex:tmcthyl

C. Germnnllenc

24) to give methoxyvinylgerInllne

compound

crystals.

atom isolated

respectively.

the teIIurium

to 84 al -72

it tellurium

and the final

and the alkylidenexclen~t~ertiiiranc

in two other

(Eq. ( I I )) utilized

of /-butyllithimm

(Scheme

and selenium.

85, regenerating

then abstracts

;IS orange

(Mb)

lo the solution.

and c;tn bc dechlo-

I-gertnaallene

tributylphosphine

in 10% yield

85 can be synthesized

( 10)). compound

The second alents

to make

tclluride

in 5% yield

82 to give

the alkylidenethiagermilane

Gertnaallene

isolated

The germaullcne

telluride

~tlkylidenctellut-agcrmirane produced

MU

of germylcne

81 in the process.

tributylphosphine

2.5

of Group 14 Heteroallenes

cyclization

of two equiva:ith

oxide

in a manner

ring 89, upon

methanol

storage

to give similat 111room

or at X0 C for 13.5 h.

(I 1)

3. HPrc,,nXl~trrli,llirlp.\ The addition w;1s investigtted like framework. stuble

of isocyanates

I -silaketenimines

starting

dimcrization

products

91, generated

by photolysis

react with four

(isoelectronic

to CO) to group

in order to set if the resulting In the lirst study, Weidenbruch from silylenes

of silaketenitnines.

isocyanates

In this investigation,

of hexa-t-butyltrisilacyclopropane

(92a-d)

(Scheme

13 citrbene

analogs

molecules would have an allencet c,1.27a,h attempted to synthesiLc and isocyanates, but only produced

25). The reaction

di-t-butylsilylene (90). was allowed presumably

to

forms

26

BARRETT

EICHLER AND ROBERT WEST

I ’ blC& MeOH 85

*

Tht-Ge-

I

I MC0

I ’ ’

% //(‘ .(“ I

87

Thr-

S~‘HI.Lll:

I -silaketenimines I ,3-alkyl isolated

when

but when

which

(depending

cyanotrialkylsilane

R =

phenyl

;1 mixture

(YSc-minor

(94a-65%)

ofthe

product)

on substituent

or dimerizc.

the steric bulk W;IS increased

dimerization. dimer

93a-d,

shifted

7-I

Only

R) either

rearrange

the head-to-tail

and 2.4,6-tri-methylphenyl

dimer (94b--45%

to R = 2,4.6-tri-isopropylphenyl

head-to-tail was produced.

dimer

(94c-76%

When

to ;I was ).

to hinder

) and the head-to-head

even more steric hindrance

was

cmploycd (also to prove that the isocyanatc KIS not simply adding twice to the disilene formed in the photolysis to make the same dimer product) by changing R to 2,4.6-tri-f-butylphenyl

(Mes”‘),

the silaketcnimine

rearranged to give compound 96. The mechanism similar isomerization with 3 2,4.6-tri-t-butylphenyl chlorostannanes

did not dimerizc.

but rather

is not well understood. but :I group W;IS also reported for

by the same group.“’

The first stable group I4 heteroallene, a I -stannaketenimine (99), was reported by Griitzmacher et al. in I 992.‘h Compound 99 was synthesized in 9 I % yield by adding diarylstannylene 97 and mesityl isocy:unide 98 in hexane (Eq. ( 12)). The bonding in 99 can be described as ;I stannylene-isocyanide adduct rather than a

Chemistry

of Group 14 Heteroallenes

(GBLI?) Si

hv -

/\

1 (t-Bu),Si:

1+

27

(1-t3u)2Si=Si(t-t~~1)2

91

(1-RtI),Si---Si(l-Utl),

:C‘=N-R

92

1

90

] T-

(t-BL+SI=C‘=N-R

H’

NR /I ../(‘\

(~-Bu)~SI,

,Sl(t-Bu)z ‘ii NR

94

96 (a) (b) (c) (cl)

RR= Rp Rp

I’ll Mea Tip Ma*

stannaethene and this is illustrated through the reactivity of99 (Scheme 16). When 2,3-dimethylbutadiene was added to 99, mesityl isocyanide 98 was displaced and compound 100 was isolated. which is the addition product of the butadiene to stannylene 97. A similar situation occurred when r-butanol is added to 99: r-butanol not only expels 98, but also replaces both of the aryl groups on tin with t-butoxy groups to give stannylene 101. RzSn:

+

:C=N-Mes

97

98

-

RzSn=C‘=N-Mes

99

(12)

R- ~.~.~-(CFJ)~C~,H:

The reactivity of a silylene 103 with isocyanides was probed by Okazaki et (I/. in 1997.‘8 When disilene 102 is heated to 60 C in THF or CfiDc,, it dissociates

28

BARRETT EICHLER AND ROBERT WEST

of silylene 103 (Scheme 27) and in the presence of various 104a-c, I-silaketenimines 105a-c are formed, on the basis of NMR

into two equivalents isocyanides results

and trapping

reactions.

Similar

to the I-stannaketenimine

just mentioned.

105a-care best thought of as silylene-isocyanide adducts and a better depiction of lOSa-c is shown in Scheme 28. Although stable in the absence of external reagents. compounds 105a-c reacted with triethylsilane to data and calculations

suggest

that

give good yields of the corresponding displacement triethylsilanc the reaction

of the isocyanidc Si-H of

bond.

isocyanides

and subsequent

The lability

105a-c with MeOH,

and silane 106, indicating addition

of the isocyanides which

provides

‘I”\

THt: 01’(‘,,D,,

102

(a) R Tip (b) R- Tbt (C) R- vcs*

I

a facile

103 across the

is also demonstrated methoxysilanc

ho ‘C’ Mea(Tbt)SI=Si(Tbt)Mcs

of silylene

Mcs

(,

2’: 103

by

107 and. in

Chemistry

29

of Group 14 Heteroallenes

III

the case of only compound normally central

105a,

is unusual attaches carbon

;I small for

amount

to the heteroatom

atom.

of compound

I -heteroallenes

The

authors

(i.e.. silicon) suggest

step of the mechanism is protonation the methoxy group at the silicon for the carbon in proving retains

108. The

in thnt the oxygen

isolation

of the methoxy

and the hydrogen

that for both

of this group

adds to the

107 and 108, the initial

of the silicon atom followed 107 (eliminating isocyanide

by attack of 10Sa) and at

for 108. Regardless of the mechanism. compound 108 is important the existence of 105a, since it is the only trapping product which

the isocyanide

that for stannaketenimine.

portion

of the silaketenimine.

silaketenimines

105a-c

In a manner replaced

identical

the isocyanides

to with

30

BARRETT

EICHLER

AND

ROBERT

WEST

2.3-dimethylbutadiene to produce compound 109. Anothercolnpound. silanol 11 1, was isolated from the reaction mixture. the cxiatence of which is proposed to be 110 durin, (7 work-up. although direct attack the hydrolysis of strained compo~~nd of compound 109 by water cannot be ruled wt. 4. Iletr,r)~)llo.s/~llcltrll~~rrr.\

EscudiC and co-workers”’ synthesized ;L mctastable I -germa-3-phosphaallenc (114) in I996 by the salt-elimination method, ;I process they called “debromollLIorination” (Scheme 29). In a reaction that was followed by “P NMR. one eyuivalent of /I-butyllithium was added to 112 at -90 C to form intermediate 113. llpon warming to approximately -60 C. lithium fluoride was eliminated. forming germaphosphaallene 114 in hS-70% yield. Compound 114 was stable up to -SO C. whereupon it dimerized in the absence of trapping agents. This process not only gave the expected head-to-tail dimer 115 (between the two Ge=C bonds), but also an unexpected dimerization product (116) resulting from the reaction

Chemistry

31

of Group 14 Heteroallenes

-60°C

-LiCI

t [ TipPhSi=C’=PMcs*] MeOtl 122 J// TipPhSJ--(l‘=pMca* OMe

tl

123

PhTip Si ’

Muh*P=(\Si,

‘(~zz,$,~~”

+

p

Pl171p

213

124

S(‘HI:MI- 30.

of a Ge=C were

performed

pected with

bond

with a P=C

methanol,

similar thesized -80 denced

providing analog,

in Scheme

method

C gave a-lithiochlorosilane by the downfield

C afforded

similar

dimer

(124)

between

and one P=C

two Si=C bond

(125)

work

experiments giving

the ex-

by quenching by making

a

112 was syn-

to that for the germaphosphaallene.

of 119 at carbon was observed

to precursor

by r-butyllithium by “P

NMR

119) and was isolated

at

(as evias the

warming 120 to -60 C. the elimination of lithium silaphosphaallene 122. Methanol addition to 122 at 123 in SO%> yield.

warmed above -20 C in the absence of trapping similar to the dimerization of germaphosphaallene bond

followed

(112). Compound

120, which

shift compared

methoxysilane

methanol,

I-germa-3-phosphallene

30. Dehalogenation

hydrolysis product 121. Upon chloride was complete, giving -60

up the

a I -sila-3-phosphaallene

by a salt-elimination

as shown

Two trapping

114: one with 117, the other with methyllithium methylgermane 118.

er o/.~” followed

silicon

molecule.

on germaphosphaallene

methoxygermane

Escudi6

bond of another

bonds

When

and the product

in a 2:3 ratio.

the silaphosphaallene

was

agents, it dimerized in a manna 124. This gave ;I head-to-tail of dimerization

at one Si-C

BARRETT EICHLER AND ROBERT WEST

127

Wibcrg (126)

ct rrl. ” havejust

to date in which

elements.

and

by adding

recently

more specifically,

tri-I-butylsilyl

warming

to -25

naallene

is separated

published

all of the atoms

arc all tin

sodium

C to provide

the synthesis

in the allene ato~m.

mixture

by fractional

9.8 h), which

or SnlN(SiMcj)?l?

crystallization

sodium

and Sn(OtRu)l

2 days.

Like

stannylcne

can be independently in pentane

the stannaketenimine complexes

can bc considered

manifests

as a mixture

at -78

One other

study

consisting

of group

I3

which

crystals

C and

the tristan-

(Scheme

to form cyclotristunnene

synthesized

by stirring

3 I ). 127

tri-t-hutylsilyl

‘C for 3 days and then at 25 C for another

mentioned

earlier.

the tendency

itself‘ in the bent structure of the resonance

of more

group

at - I96

from

as blue

ing to the authors, is best described as structures and isolation of this I ,2,3-tristannaallene illustrates other heteroallenes

heavy

126 was synthesi&

of compounds,

Care is taken not to warm 126, because it rearrange5 (r j I2 =

only hctcroallene

are

Compound

to Sn(OtBu)l a

ol‘the

hachbone

structures

126sd

4). which

and. accord-

126b and 126~. The synthesis that it is feasible

than one heavy

I4 heteroallcnes

of tin to form

of 126 (Fig.

involving

group

to synthesis

I4 atom.

transition

metals

was rc-

ported in 1995. Jones VI trl.3’ described the isolation of a ruthenium complex of‘ a I-silaallene (132-Scheme 32). The I-silaallene also interacts with a hydrogen atom as well as the ruthenium metal center. Jones rt tri. describe this view

Chemistry

of Group 14 Heteroallenes

33

126a

i/* ..

.. R:SnHsnN

SnR 2

RISn

fSnNSnR, 126~

126b

/

.. kS”.\snR Rg+l’ 126d

Br ‘h?C=C

/ \

n-BuLi ‘SiHMq

128

LI

/

Ph:c‘=C

-70°C

‘SitIbIs

129

c’p*( P(‘y3)RuC‘I

LI(‘l

I

130

(a) L= (‘y (b) Lp Ph. Me, Me

LP \R/Cp* / : \\.

Ph2C=c’

132

\:.,‘H

i

c’Y,P p* Ph&‘=C’

/

\ Me?Si-H

ziq 131

34

BARRETT EICHLER AND ROBERT WEST

as “a I -silaallene

that is stabilized

metal-hydrogen

bond.”

intermediate

129, to which

131 which arrested

above

later.

exchange

45 C led to multiple

yielding

structure

of’

in C&,

decomposition

a

intermediate atom was

so than

similar

lor I day. and did not react with

be performed

132b without

with to give

132a was obtained

132a was stable (more

to 45°C

could

Xl %) to form

and interaction

at low temperature

atom from the silicon

crystal

Compound

upon warming

(PLj)

warming.

ligation

(130) was added.

An X-ray

atom.

be discussed

CO. Ligand (with

Cp”(PCy~)RuCI

by the ruthenium

silene complexes)

metal

128 was lithinted

132a (42%) after the hydrogen

produced

and will

by both

Compound

by replacing

PCyi

harming

the silaallene

products

unreported

with

PMe,Ph

moiety.

Heating

by the authors.

IV PHYSICAL A. X-ray Structure The crystal vide valuable

PROPERTIES

Determination

structures”.’

of a variety

information

toward

of‘ heteroallenes

the understanding

have been solved of the bonding

and pro-

in this series

of molecules. If one were for an allene

to ask a first-year (C=C=C)

All things

considered.

all-carbon

allene”

should they

(133)

bond

lengths

before, more This

on

would

with

be noted that due to crystal

a

capon

substitution

this case as bending (Table III). In three studies

but how

two and

much

values

of 179.0

may deviate

slightly

the early

shrink

in Table

was

or an

III. It must

the bond angles and

from the ideal. As mentioned state is

of the allenc.

N) hcteroallene

angle

will be

agrees with theory

in

(I 79 ) to tin ( IS4

suggested

that

)

I -silaallencs

framework. Later calculations by Trinquier and that the I-silaallene framework would be nonwould

59a, which (Table

is listed

From carbon

I~XOS,~~“~“’ it

angle

degrees.”

and an example

atom. Experiment

deviate

were seen with the isolation

I-silaallenes 56 and 172.0 . respectively

“IX0

in the one position

Ce. Sn; E=C.

systematically

the moiety

the bond

(C < Si < Ge < Sn < Pb). the singlet

(M=Si,

would have a linear Si=C=C Malricu’ predicted qualitatively linear.

be correct.

what answer

forces and steric restraints.

with a heavier

angles from

likely

angle

student

most likely

state for the atom

means that the M=C=E

quantitative

bond

the group

over the triplet

chemistry

most

packing

of these molecules descending

favored

bent more

organic

be. they would

III).

from

IX0

and structural

was unclear. determination

The

First of the

have very similar Si=C=C angles of 17.1.5 This is an average deviation of 7.3 from

linearity-signiticant, but relatively small the germanium and tin substituted allenes.

compared

to the deviations

shown

by

Chemistry

35

of Group 14 Heteroallenes

MC

I<,,‘,, (.=(

=(.’ \

VICd

PI1

133 R- (blC)C 4-(‘1

I70.0

?OO.O

l.il3LJJ

I ilXii)

34

173.5

.360.0

I .701(J)

1.3:!45)

20

I so.2

i-Ix.4

1.7X%2)

1.3147)

2-I

I.S.3.‘)

700.0

237(i)

1.1’8r.31

2h

I’h)Mc

1-P

1-1’1

, \__I

\IC\‘/,, SI==( =c I-.\d’ 56 1-1’:1.’

:I

1-1’1

I-l3Ll

“Ph.

/

(;c=c’=(’

\

-r,p’

16

I’ll MC\

I< I/,,

/

Sn=C‘=N I<’ 99

The I -silaallene calculations preceded the isolation of’the by 12 years, but despite the isolation of’ a stannaketenimine

first stable silaallenc in 1992’” and a ger-

tnaallene in I 99X,‘J no calculations yet for analogs larger than silicon.

of bond angles or lengths have been perf’ormed Given some guidelines and values provided by

Trinquier

calculation

and Malrieu,3

;I simple

can be performed

(Scheme

33) to

36

BARRETT EICHLER AND ROBERT WEST

predict whether or not a parent group 14 I-heteroallene will be linear or bent. Consider the example of a I-germaallene. According to the above authors, if ON% tn ) > CAEs+r (condition I). the structure will be linear, and if O.S(E,,,) CAEssr (condition 2). the structure will be bent. E,+, is the strength of a typical 0 fn planar double bond that is to be formed and C AEssr is the sum ofthe singlettriplet energy separations for the two fragments being brought together. Using values from the Malrieu/Trinquier paper, C AEs- r (68.5 kcal/mol) is larger than @SE,, 7r) (45-53 kcal/mol) for the parent I-germallene, satisfying condition 2. Therefore, germallenes should be bent. This is the case for germallene 76, which has an M=C=C angle of 159.2 This deviates from linearity by 20.8 , more than twice that for the silaallenes. Stannaketenimine 99 deviates by 26. I , although the nitrogen atom in the 3-position may affect this angle. Tristannaallene 126 is bent to a similar degree. 155.8’, although the emormous supersilyl [ Si(t-Bu),] groups may prevent more severe deviation from a linear geometry, and Wibergj’ has proposed that there may be a contribution to bending from the lone pair on the central tin atom. In order to achieve maximum orbital overlap between atoms M and C in bonding model B (Fig. 2) the plane made by RzM bends away from the vector made by the M=C bond (Fig. 5). resulting in pyramidalization of atom M. A simple test of the extent of pyramidalization at a particular atom can be performed by summing all of the bond angles around M and comparing the result to the ideal of 360 ’(for sp’ atoms). The sum of the bond angles in allene 133 around the I -position carbon total up to be exactly 360.0 , as expected. An unexpected result is that silaallene 56 also totals 360.0 around silicon, whereas silaallene 59a bond angles add up to 357.2 Germaallene 76 deviates somewhat more from planarity with a total of 348.4 The sum of the bond angles around tin in stannaketeniminc 99 comes to a meager

Chemistry

of Group 14 Heteroallenes

37

290.9 , indicating a severe distortion from planarity. even surpassing the pyramidalization of an idealized sp3-hybridized atom (3 x 109.5 = 328.5 ). Tristannaallene 126 averages 344.0’ for the angles around the I - and j-tins. These angles are much smaller than for the stannaketenimine. but pyramidalization around tin may be prevented due to the severe steric constraints caused by the large tri-tbutylsilyl ligands. Trans bending of the substituents and bending at the central carbon for silaketene (H$iCO) become dominant for its calculated structure.” The Si-C-O angle is calculated to be 167.4 and the angle created between the Si-C bond and the vector bisecting the two Si-H bonds becomes a very sharp 89.0 The calculated bond lengths for this yet unseen moiety are I.891 A (Si-C) and I, 14X A (C-O). The reason group 14 heteroallenes were not isolated until 1992 is undoubtedly because of the reactivity of the M=C (or M=M in the case of the trislannallene) double bond. Four Si=C double bond lengths were calculated in the early 1980s for I -silaallenes; I .696 r\ by Lien and Hopkinson,’ I.703 w by Gordon and Koob.(’ I.702 A by Krogh-Jespersen,“’ and I .62 r\ by Ishikawa rt rrl. “‘In excellent agreement with the majority of the theoretical results, silaallene 59a has a Si=C bond length of 1.693(3) A and silaallene 56 has a bond length of 1.704(4) A. Although no calculations have been performed for germa- or stannaallcnes, comparisons can be made to germenes and stannenes. Germaallene 76 was found to have a Ge=C double bond length of I .7X3(2) r\. which falls right in the middle of values observed for germencs 134 [ I .827(4)].1’“.’ 135 [ I .X03(4) A],3h and 136 1I .77 I ( 16) r\]j7 (Table IV). Amazingly, the Sn=C double bond length [2.397(j) A] in stannaketenimine 99 is longer than both of the Sn-C single bonds [2.306(2), 2.314(j) A] to the ipso carbons of the R groups and is considerably longer than most other reported stannene Sn=C bond lengths 1137-140; 2.03-2.38 r\, Table V]. The long Sn-C bond length in 99 reaffirms that the bonding interaction between tin and carbon is weak and is best described as a stannylene-carbene adduct. Tristannaallene 126 has an average Sn=Sn distance (two Sn-Sn bonds per molecule and two diastereomers) of 2.68 I\, which is the shortest Sn-Sn bond length next to its rearrangement product cyclotristannene 127 (2.59 p\) (Table VI). The synthesis of three silaketenimines 105a-c prompted Tokitoh and Okazaki’s to calculate the optimized geometry of a model compound, Ph$iCNPh. This model reinforced that 105a-c are truly Lewis acid-base pairs, with the isocyanide donating its carbon lone pair to an empty p-orbital perpendicular to the lone pail

38

BARRETT

AND

ROBERT

WEST

I .X03(4,

730

1.771l101

37

l’hl

1 bl ‘< I I,,

EICHLER

‘(.‘=( / ‘~

+/ ls/’

‘\

I ip

136

and two phenyl distance bond,

substitucnts

on silicon.

( I .X63 ,&)13’ bond and the Si--C=N

C(isocyanide)

angle

Si-C(isocvanide) isocyanidc

length

bond

binding

is bent (163.4

These

energy

than even tin average

I .8X2 d, is predicted

angle

is 99.4

A long [longer

bonds

for the Si--C(isocyanide)

). The average

and

Si-C,,,.:

angles.

C(Ph,,,,,,)-Si-

along

(25. I kcal/~~~ol). rcaftirm

with

3 weak

that this is ;1 silylenc-

adduct.

The C=C

bond oi‘the

heteroallcne

because

ol‘ its lack of reactivity,

double

but should

tigation

of these compounds.

In calculating

moiety Si=C

the three athremcntioned groups also calculated A by Lien and Hopkinson,’ I.296 I\ by Gordon Jespersen,“’

and I .29 A by lahiknwu

is often double

76 has a C=C

double

As noted

(59a).

bond length

[ I .3 l4(2)

by Griito~~acher

bonds

the C=C

rt trl. “’ Although

inves-

l’or I -silaallenes.

bond lengths: I .3 I2 I.395 A by Krogb

isolated

I -silaallene

C=C

lengths, they are at least A for 59a. Germaallene

r\] only 0.01 A shorter and co-workers.

in discussion\

in a thorough

and Koob.”

double bond lengths are slightly longer than the calculated consistent with lengths of I .324(s) A for 56 and I .325(3) analog

ignored

not be overlooked

the C=N

than its silicon bond

length

[ I. 15X(3) r\] for stannaketenimine 99 is “typical for isocyanides.“‘h The structures of two group I4 heteroallenes that are complexed

to other atoms

have

(132a)

been

determined-a

ruthenium

complex

of a I -silaallene

and

a

Chemistry

39

of Group 14 Heteroallenes TABLE

V

S-TANNFNF BON) LENGTIIS

M=C Len$h

(.A,

t-r&l I

(Me3Si):HC \ /

(Mcisi)zllc‘

,P\ Sn=c

C‘(SiMe;):

3.0?5(4)

\I3/ I t-Bu

137 t-Uu

17h

3.032(5 1

tellurium bond

complex

length

for silaallenes Si-C(sp’)

of a I -germaallene

of I .805(6)

A, which

56 (I ,704

single

bonds

gests an sp’-hybridized authors

propose

drogen

atoms,

.&) and 59a

(I .693

than

but is still

central

carbon,

bond

that this molecule

bond angle

between

stabilized

length

of

lengths

than

normal

12X.6(4)

allenic

ruthenium,

is not only bond

the bond

shorter

not an sp-hybridized

atom but also by a hydrogen atom. Compound 86a has a germanium-carbon is shorter is longer

A),

longer

.90 1\).31 The Si=C=C

‘-electron

132a has ;I silicon-carbon

Compound

(I .85-I

a 3-center indicating

(%a).

is considerably

carbon.

silicon,

bugThe

and hy-

by a ruthenium 1X3(2)

r\,

which

than Ge-C single bonds of germirane derivatives ( I .92-2.07 A).“’ but than the Ge=C double bond lengths listed in Table IV ( I .77-l .83 A).

The relatively angles sum to

short

Ge=C

354.4 (which

bond and the fact su ggests considerable

that

the

three

sp’character

C-Cc-C at germanium)

bond led

40

BARRETT EICHLER AND ROBERT W E S T

(Mc;Si)zH(’

127 \

(Mc;Si)211(‘

( Mc;Si)JSI

/

1.. SI(SIMc~);

142 \ II/

145 [R

‘(‘H(S~fvlq,~

/

(Me;Si);Si

,U-I(SIM~~)~

St1=St1

1.Xx7(h)

-1Xh

2.X3.7(I )

4xc

Ii

S,,ZSn/ 1.. SI(SIM~);

[(‘(H)SiMel((‘pHiN)]~I

the authors to propose that this molecule is in fact a n-complex of a tellurium atom with the Ge=C double bond of a I -germaallene. The Ge=C=C bond angle is 149(l) ‘, almost directly in between the bonding angles for sp- (180 ) and sp’-hybridized (120’ ) carbons, and is only IO larger than the Ge=C=C bond angle of I -germaallene 76. 6. NMR Spectroscopy

Possibly the most characteristic piece of information one can obtain to prove the existence of a I-heteroaallene is the central carbon “C NMR chemical shift. This carbon chemical shift is very deshielded. typically being greater than 200 ppm,‘” which stands out from most other carbon resonances in a normal organic molecule. Most of the group I4 I-heteroallenes listed in Table VII have shifts greater than 200 ppm. Also, as the heteroatom becomes larger, the resonance moves farther downfield.

41

Chemistry of Group 14 Heteroallenes TABLE VII ‘-‘C CIII:b4lCAl. SkllFTS 01. CkNTRAI. CRKHON OR (;ROL~I’ I-! ~-H~:ERoALL.~.N~:s I -Heteroallcne 56 5% 5% 59C

70 73 76 85 I osa 105b 10%

114 122

’‘C. vhit’t of Cenual 225.7 175 7 -__ 216.3

227.0 228.2 237. I 235. I 343.6 209.2 IY6.6 I7X.S 2x0.9 769. I

Carbon

(ppm)

Reference

20 2.3 2.3 73 72 72 7-1 2hb 2x 2x 2x 29 30

The I-silaallenes in Table VII have chemical shifts in the range of 2 16 to 237 ppm. It is interesting to note how changing a tert-butyl group to a phenyl group on the carbon end of silaallenes 59b and 59~ can change the chemical shift by greater than IO ppm. but when the two phenyls of 59c are changed to a fluorenyl group (70), the chemical shift moves by only 0.3 ppm. Germaallene 76 is the exact germanium analog of silaallene 59a, and this substitution of germanium for silicon relocates the central carbon shift almost IO ppm downfield to 235. I ppm. Adding a phosphorous to the 3-position of a germaallene (giving germaphosphaallene 114) moves the central carbon chemical shift a substantial 45 ppm to 280.9 ppm.” Changing the germanium atom to a silicon (112) moves the silicon back upfield to 269. I ppm. The central “C shift for model silaketenimine Ph$iCNR was calculated to be 17X ppm. which agreed especially well with the shift for 10% (178.5, 105a = 209.2 ppm, 105b = 196.6 ppm). Reiterating the idea that the n-complexes 132a and 86a are not truly heteroallenes, one must consider the central carbon ‘?I NMR chemical shifts. Silaallene complex 132a starts to approach allene status with a chemical shift of 175.5 ppm, but the most deshielded carbon for alkylidenetelluragermirane 86a is only 153.04 ppm. Another useful tool for analyzing the structure of heteroallenes containing silicon is ‘%i NMR. Typically. sp’-hybridized silicon atoms have a chemical shift *Although it is not 3 group I4 heteroallene. arsapho\phaallene” Mes*A%=C=PMes* (+29Y.S ppm) over-emphasizes the point that the central carbons of heteroallenes are gently de\hielded. For reference. I-phovphaallene”3 Mes*P=C=CPhz has n central carbon shiii of f237.6 ppm and 1.3. dipho\phaallene’” Mes*P=C=PMes* h;l\ il shift of +276.2 ppm.

42

BARRETT

MQSI

EICHLER AND ROBERT WEST

,OSIMt2:

\ Si=(

\

Me3Si’

146

-II 2

147

144.7

I-13u

SiMe:

Me, Si=(”

\

MC’ I-Bu,

SIMe(t-r3u)z

Mes s,=si’

Mes’

cis,trans-14X

\

04.7 (Cl\), 90.3 (Irm\)

I-DU

MW,

MW Si=Si

’ \

MW’

63.7

149 Mos

13 I 16.2 4x.4

5Ya 13 56 5Yh SYC 70 122

downfield with

of +I0

respect

5s. I 5x.7 4x.0 s7.7

ppm

(with

respect

to tetramcthylsilane)

to sp3-hybridized

silicons.

of + IO ppm.

This

by two examples

(Table

and silaallenes

VIII).

Brook’s

silcne

electron

density

is evidenced

(146)“‘”

which

are no exception.

through

at the silicon

the resonance atom

usually

and have

each of silenes”

I -Silaallenes structure

than does Wiherg’s

are deshielded

resonances

have been compared

in Fig. 6. which silene

(147),J’h

shifting the resonance farther upheld than the analogous ailene. The chemical shifts are definitely closer to Brook’s silene than Wiberg’s.

R;Si

upfield

and disilencsJ5 puts

to

more

thereby silaallenc

Chemistry Replacing dramatic

a carbon

change

silaketenimine measured

with

upfield

Ph2SiCNR

in different

lo%-c

a nitrogen

ofthe

(-47.9

(6 = -38.9

-57.9

to

shit’&

also follow

(aryl)

by changing silaallenc

silicon

has

alkyI/aryl 59~1, with

This

ing rhe composition more)

on the ‘“Si chemical position

3 to

a

range 01’48

I‘ragment

pp111.

to

carbon

similar

to

silaallcne\

and

16.1 (73) ppm.

of’heteroallencs. much

as

chang-

of’ an et’fect (if’ not

a suhstituent.

Switching

122) moves

on silicon.

59b, with one

those for the two diary1

is the most deshiclded

it has two aryl groups

upfield

of 55. I. whereas

substituted

SC) ppm;

can have

and there

in silaallencs

( I .i. I ppm).

at 13. I (59a)

(silaphosphaallene

which

shift

alkyl/aryl

upfield

group

shift moves

Silaallene

uptield

ppm

on the

but when

is also observed

chemical

shift 215does changing

phosphorus

to 75.7

to date, even though

40

effect

(alkyl)

the chemical

shifts for the central

of the allenc

bon

values

and silaallencs

near 90 ppm,

shift

Ibr all of’the

arc considerably chemical

large

shilis

resonances

silaallenes

shift downfield

one tert-butyl

shift

has a “‘Si

two aryl groups.

Like the ‘?.I NMR

at

with

to diary1 substituents.

on silicon.

(56, 59b, 59c, 70) lie in the narrow substituted

;I

silaketenimines

such as disilenes.

chemical

subslituents group

that of the disilenes.‘“Si

for

to have a significant

atoms

(148)

‘“Si

;I

30 to 63.7 ppm.

and one aryl

to the observed

temperatures

(149). ‘5’1 in this case mesityl,

by approximately alkyl

was close

vs aryl-seems

The disilcnc”

group

are two aryl groups

ppm)

causes

‘“Si shift in model

ppm).

of sp’-hybridized

this trend.

one mcsityl

of a I -silaallene

shiti. The calculated

and at various

The type ofsubstituent--alkyI chemical

in the 3-position

‘“Si chemical

solvents

43

of Group 14 Heteroallenes

%i

the car-

the ““si chemical

shirt for a silaallcne

which

should

keep the shifl

upfield. The

central

considerable range

tin

of monomeric

+2313),‘“”

R =

The terminal =

+374

shift

in tristannaallene

character,

stannylenes

ppm).~7h

[ 140

=

(6 =

R2Sn=SnR2

f710 (R =

shifi

supports

is +2733

that

tin

has

is in the

(Me~Si)~CCH2CH3C(Si.Me3)2

(6 =

R/R

(+X)3

p~iii).~“’

ppm.

this

which

(6 = +332X),““”

rin aloms have achemical tins

126

as its value SnR2 IR,

[CH(SiMej)l]

three-coordinate (6

““Sn

stannylene

= Trip/Tbt

ppm)

137

Tip. 0 = +437

(6 = +220X)].‘“’

nearothersp’-hybridized, (6 =

+X35

ppm),‘ih

13X

ppm)““j.

FUTUREPROSPECTS How

might

I -silaallenes

this is fairly

lield well

develop

in the future?

understood,

At this

time,

and that of’ I -germaallenes

the chemistry

of’

is at least par-

tially explored. Perhaps the series can be extended to I-stannaallenes, but these are predicted to have quite limited stability. The isolation of the I .2.3-tristannaallcne shows

that any combination

of heteroatoms

may

be combined

to form

allenes

44

BARRETT

EICHLER

AND

ROBERT

WESl

and the series may be extended to silicon or germanium. 2-Heteroallenes are predicted to be less stable than their l-isomers. but nevertheless may be isolable. 13Diheteroallenes, on the other hand, should have stability comparable to the known I -heteroallenes, and are therefore attractive targets for synthesis. Examples already known arc the 13phosphasilaallcne and phosphagermaallcne described in Sect. IIIC4. Since stable silaketenimines and a stannaketenimine have been synthesized, it seems that germaketenimines should also be available. The synthesis oftin heteroallenes indicates that lead analogues may soon be included in thi:, c/as\ of interesting molecules. As yet there is no firm evidence for heteroallenes of the group I3 elements: these are likely to be investigated in the future. Finally. the flash photolytic studies of silaallenes which have provided much insight into their formation (see Sect. IIIA2) will probably be continued and expanded to include other members of the heteroallene family.

RI:I.I:KEN(‘ES

(3) (4) (5) (6) (7) (X) (9) ( IO) (I I I

Trinquirr. G.; Mall-ieu. J.-I’. .1. Aur. (‘II~I. Sw. 1987, 109. 5303. Barth&t. J. C.: TI-inquirr. G.: Bcrtrand. C;. ./. A/II. Clrcw. So,. lY7Y, /O/. 3785. Lien. M. fl.: Hopkinaon. A. C. Clwur. P/T!,. Idr/f. 1981. SO, II-I. Gordon, M. S.; Kooh. R. D. J. h. Clrcm. Sot. IY81, IO.?, 1939. Maier. G.: Pad. H.; Reihcnauer. H. I? Augcx C‘lwr~s. Irrf. fd. Eqq/. lYY5, .I-!. 1439. Maier. G.: Rciwnaurr. H. P.: Egenoll. Ii. Or~str,~o,l~~,fr////~.\ 1999, IS, 2 15.5. Apeloig. Y.: Knrni. M. J. hr. C/MI. SW. 1984, /Oh. 6676. Krogh-Jespersen. K. J. (‘on~p. ~‘hw. 1982, 3. 57 I Cioslow\ki, J.; Hamilton, T.: Scusxia. G.: He\\.. 13. A. Jr.; Hu, J.; Schaad. L. J.: Dupuis. M ./. hr. C/W,?l. .SOC~.1990, I /,7. 31 x3. ( 12) (a) lahikawa, M.: Fuchikami. T.: Kumada. M. .I. Arx C‘lrrw. .Soc 1977, YY. 245: (h) Ishikaw. M.: Sugisawn, H.: Yumnmoto. K.: Kumada. M. J. O~:qtrrrowr. (‘lwu~. 1979, 179. 377: (c) Ishihaua. M.: Nishimut-a. K.: Sugiuwa. H.: Kumada. M..I. Or:~or~owr C‘l~eu~.1980, IYJ, 147:(d) Ishihawa. M.: Ni\himum. K.: Ochiai, H.; Kumada. M. ./. Oqruww~. Clrcw. 1982, ?.?h. 7: (e) I\hikwa. M.: Kwnr. D.: Fuchikami. T.; Ni\himura. K.: Kumada. M.: Higwhi. T.: M~yamoto. S. ./. A~rr. Ciwru. Scw. 1981, 103. 2124: (f) Ihikawa, M.: Sugisawa, H.: Fuchikumi, T.; Kumada. M.: Yamahe, T.: Kawahami. H.; Fuhui. K.: Ueki, Y.: Shi/uka. H. ./. Aw. CIwn. So<.. lY82, IO-I, 2872: (g) Ihhikawa, M.; Sugisawa, H.: Kumada. M.; tiiguchi. T.: Matsul, K.: Hirota K.: Iyoda. J. O,;~tr,l~,n~rf~l//ir,.\ 1983, 2. I7-1; (h) IShikawa. M.: Matwawa, S.: Hi!-otw. K.: Kamitot-i. S.; Higuchi. T. O,-gr~nonrc,/~t/li[,v 1984, .i, 1930; (i) I\hikoua. M.: Mathwaua. S.: Higuchi. ‘I‘.: Kamitori, S.: Hirotsu. K. Or~~“~~j/~~“/o/l;[,,\ lY85, 4. 2040: (j) Id~ikawa, M.: Sugisanu. H.; Iiorata. 0.; Kumada. M. ./. Or,cyuwmct. (‘/rem. 1981, 217. 43: (k) I\hikawa, M.; Ohshita. J.: Ito. Y. Oigi~,~o,,~~f~~//ic~\ 1986, 5. IS IX. ( I3) Brook. A. G.: Brook, M. A. A&. O~~~trm~~rraf.Clrcm. 1996, .jY, 7 I.

Chemistry (I-I)

of Group 14 Heteroallenes

45

(7X) (29)

(a) Ishikawa. M.; Fuchihami. T.: Kumada. M. J. AUI. C/rc~r. Sot. 1979, 101. 1348: (b) Ishikawa. M.: Sugisawa. H.: Fuchikami. T.; Kumada. M.: Yamabe. T.: Kawakanli, H.: Fukui, K.: Ueki. Y.: S.: Sugi\awa. Shi/uka, H. ./. 4rn. C/lrv?~. Sot. 1982, 104. 2872: (c) Ishihawa. M.; Matsuawa, H.: Yano. F.: Kamitori. S.: Hlguchi. T. J. -\r~. Chcvn. Sot. 1985, /07. 7706; (d) lahiknwa. M.: Ohshita. J.: Ito, Y.: lyocla. J. ./. AUI. C‘hrr~~. Sot. 1986, /OX. 7117: (e) Ohshita. J.: Isomura. Y.: I\hihawa. M.: O~~cl,lo,rrrttr//ic,,~ 1989, h’. 70.50: (f) I\hihawa. M.; Nomura, Y.: Torakl. E.; Kunai, A.; Oh\hita. .I. J. Oqonc~ncv. C’lxv~. 1990, -
(30)

Rlgon.

(15) t 16) ( 17) (IX) f 19) (20) (21)

(22) (23) (21) (2% (26) (27)

/i. 3070. L.: Ranaivonjatovo.

H.: EvxdiC.

J.: Duhourg,

A.; Drclcrcq,

J.-P. C‘lrc~rr. E/c/: ./. 1999, .i,

771. (31 1 Wiberg, N.; Lerner, H.-W.; Va\i%ht. S.-K.: Wagner, S.: Karaghio\toff. K.: Niith. H.: Ponikwx. W. ht: J. /wy. C‘lrrm. 1999, I2 I 1. (12) Yin. J.: Kloain, J.; Abboud, K. A.: Jane\. W. M. ./. 111~. Clrctv. Sot,. 1995, 117, 3298. (3.3) For a recent review of structure\ of main group multiple bonds. vx: Power. P. P. C/x,/a Kcl: 1999, YY. 3463. (34) Groth. P. Aa Chr,,~. SU&. 1973, 27. 3302. 1.35) (a) Meyer. H.; Baun~, G.: Massa. W.: Berndt, A. i\rlgcr~: Clinv. /,lt. EC/. &g/. 1987, 26, 79X: (b) Meyrr. H.; Baunl. G.; Mama. W.: Bergcr, S.: Berndt. A. An~c’n: C/?c,~r. /rz/. EC/. keg/. 1987, 26, 546; (c) Berndt. A.: Meyer, H.: Baum. G.: Massa, W.: Berger, S.: PUI? A/J/I/. C‘lrm. 1987, 5Y. IO1 I. (36) Lazq, M.: Escudi6. J.: Couret. C.; Sat@, J.; DIGiger, M.; Dammel. R. Aqgrn: C/le~l. /nr. Et/.

Eq/.

1988, 27, 828.

46

BARRETT

EICHLER

AND

ROBERT

WEST

ADVANCES

IN ORGANOMETALLIC

CHEMISTRY,

VOL. 46

“Very M ixecFMetal Carbonyl Clusters SUSAN M . WATERMAN,

NIGEL T. LUCAS, and MARK G. HUMPHREY Department of Chemistry Australian National University Canberra, ACT 0200, Australia

I. II.

III.

IV. V.

Into-oduction Kcacti\ity Srudic\ A. General comment\. B. Ligand Substitution C. Ligand Addition. D Lipd Tran\fot-mation?. E. Core Transformation\ F. Catalytic Studie PhyGcal Measuremcnta A. General Comment\. B. Fluxionality C. Electrochemistry. D. Othct- Physical Methods. Conclusion and Outlook Appendix: Abbreviation\ IWerence~

37 38 3x 49 64 07 79 I Oh I IO I I6 I I6 12s 130 I35 IX> I17

I INTRODUCTION Transition reasons.’

metal

carbonyl

The oil crisis

catalysts

or models

research

since that time.

clusters

facilitates

complexes. molecules potential

for catalysis, substrate

a

attracted

interest

encouraged

interest

for

coordination not readily

of metal atoms within of accessible

as “electron

reservoirs.”

a

oxidation

a number

in clusters

and this has been an enduring

transformations

large number

to function

have

The multimetallic

The aggregation with

clusters

of the mid-1970s

theme

of organic achievable

metal cluster

in cluster

molecules

at

at mononuclear core can afford

states which

Fluxionality

of

as pre-

at metal

may have the clusters

may

provide an effective model of substrate mobility at surfaces active as heterogeneous catalysts. As clusters become progressively larger in sire. they may be expected to adopt metallic character, and the intermediacy of a “metametallic” potentially interesting physical properties has been proposed.’ The pre-eminent

factor controlling

has been the existence

or otherwise

the development of efficient

state with

of areas of cluster chemistry

routes into the clusters

themselves.

47 All rights

Copyright c 2001 by Academic Press. of reproduction in any form reserved. 0065-3055/01 $35.00

48

ef a/

WATERMAN

Most

early

syntheses

has been effective metal

clusters.

clusters

have become

environment

for a number and structural

of physical

properties

A significant or ad,jacent

parate

metals

afford

such clusters

above

would

have

activation, more

clusters

comprised

A number

aspects

as

groups.

for

group

4-10.

from

properties transition

metals

(PGM)

with

affect

catalyzed

actitrans-

metals.

appeared.xm”

containing

review

and

exalnples

clusters

has recently

carbonyl

by three or more

this definition

is somewhat

are coupled

to non-PGM.

arbitrary.

metals, synthetic

to 19% inclusive.

mixed”-metal

separated

However,

similar

summarizing

9 heterometallic

metals

substrate

discrimination

late transition

have

a

of “very

if

metal

precatalysts.

clusters

published

clusters

and should their

to listed

an electropositive

facilitate

clusters

h-group

homometallic

heterogeneously

metals

dis-

procedures

bond may enhance

may

although

the same

of the properties

of reagents.

Many

from

incorporating

as synthetic

coupling

(which

aspects,

metals

and a number

on mixed-metal

While

ligand

have focused

and investigations

clusters

may bc effective

containing

and physical

groups

that platinum

contain

is surprising.

is possible).

of group

those containing

defined

This

of hcterometallic

” This review.

studies

mixed-metal

for a range

and structural

on the reactivity

reactivity

clusters

processes

been

site selectivity,

rare.

to mid-transition

of reviews

reactivity

appeared.

systematic

For example,

of these metals

has largely

or on synthetic and

early

of the heterometallic

activation,

to show sharp differences

for fluxional

to a range of mixed-metal

the signiticancc

metal to give a polar metal-metal

couple

the focus

of Stone

are now well established.

than one process

formations

analyses

advances

etc.), but thus far most reports

reported.

and metalloselectivity

energies

when

been

is very different.

and electronegative

theoretical

but far fewer

be expected

the heterometal

to the pioneering

of mixed-metal

groups,

for mixedmixed-metal

and the experimental

(substrate

arc comparatively

number

group

studies:

to synthesize

groups.3~~7 Access

responses.

not surprisingly.

but is less useful

procedures

to assess

of properties

electrochemical

on synthetic

research

the possibility

type which,

clusters

due largely

and others,

and their

affords

mobility,

available,

and Mingos

and Vahrenkamp, clusters

it and hope”

In the last 20 years, general

by Hoffmann

vation

were of the “heat

for a range of homometallic

focuses clusters. d-block it ensures

II REACTIVITY

STUDIES

A. General Comments L&and viewed,

activation but

few

and transformation of “very

examples

at heterometallic mixed”-metal

clusters have been rcclusters effecting these

“Very Mixed”-Metal

transformations mations

were identified

at “very

aubsequcnt activity

of “very

particular

mixed”-metal

tion. and substrate heteromctallic below

bond-,

proceed

LO ligand

addition,

overlap

types

were published

metalLmctal

bonds

or unique

substitution

and so have been mentioned

rcacGona

corresponding

reactions

of studies

to

active-

in the seclions

intermediates

exchange

A number

reagents

substrate

classifications with

in the re-

of directing

is unavoidable:

01‘ metal

intermediates.

Iransfortnations,

the polar

Iran&r-

interests

enhanced

the reactivity tncchanisms.

and cerlain

way of core-expanded Iigand

some

by associative

major

are the possibility

utilizing While

of ligand

in this Chapter above,

or face-specificity),

transformation

are self-explanatory,

all reports

summarized

As mentioned clusters

environment.

frequently

volve

clusters

review.

sites (metallo-.

almost

at the time;”

mixed”-metal

to the earlier

49

Carbonyl Clusters

cart occur

by

catalysis

in-

modeling briefly

in both rclcvant

seclions.

B. Ligand Substitution . ot dtttering

The presence into ligand disparity

substikttion: between

core also reduces rendering

The

the effective

the possibility

should

be enhanced

introduction

of differing

symmetry

ligands

isolated

mobility.” clusters

in Section

have involved

ties provides

availability

phosphines

from

range

of steric

which

ing samples Studies tr-

suitable

for single

substitution ot’ phosphinc

or ~etranuclcat-

at “very

crystal

clusters.

X-ray

mixed”-metal

substitution

studies. clusters

all trimetallic

of organotnetallic

and electronic

have delined

proper-

of site- and the substitution

cluster; instead, phosthe prospects 01‘obtain-

The results

of’ phosphine

arc summarized

have thus far focused

with almost

II.B.2.

investigations

sites of‘ ;I range of phosphines at a “very mixed”-metal phines have frequently been employed solely to enhance phosphite

mixcd”-

;tnd these are sumtnarkd

in Section

out syskmatic

but there are few studies

metal

due to donot

ot’ “very

the most fundamental

a broad

by core

predicted

studies

or phosphitcs.

are considered

of carrying

those

the

and others

have met with

clusters labilika

substitution

are among with

the possibility

mctallo-selectivity,

of ligand

ligands

and phosphites

Their

differ

clusters.

and nfi’ording

by Vahrenkatnp

of substitution

ofien

majority

I1.B. I All other

Phosphines reagents.

The

products

homometallic

in mixed-metal

a sequence

the

into a cluster

metals

inequivalent.

Attetnpts

of site rcactivitics”

but although

of metnlloselectivity upon accentuating

over that ofrelated

sites for incoming

a “hierarchy

success,

GUI be defined, metal

introduces

of site- as well as metallo-selectivity.

to define

ligand

the metals.

coordination

prospect some

metals

this selectivity

almost

examples

in Table

excltusively

pseudorctrahedral

and I. on

::

TABLE

I

It SI’BSTITI TIOK -\T VEKY MIXtt)-MEr-\L

CLL’STFRS

[Mot&(/r ~-CC0~menth~l)(CO)7(L)(~/‘-CiHi)l 1I. = P(OM+. PQ3] (1LloCo~(,i~-CCO~menthyl)~COl~,~~~rphoiJ~,~~~L)](L = CH,Pr’. C,,H-i [M~CO~(~:-CCO~PI-‘)(~~-L)(CO)~(I~~-C‘~M~~)~(L=dppr. arphm) [WCo-.(/t ~-CMej(CO)?(PHPh2)(~li-C,H,,] [WCol(/r :-CC~,H,Me-J)(C0),(PMe2Ph,r,li-L)I (I-=CiHi. CsH$5iMq) IWCO~(II:-CC~H,M~-~)(CO)~,(L)~~I~~~L’)I il.= PMqPh. L’ =CiHi. C>H,SiMr;: 1. = P(OMe);. 1.’=CiHi, IWCol(,l7-CChH,Mz-l)(~c-dpp1ll)(CO)(,r,i~~L)] (L. = C’5H>. CjH$5iMr;) [WCO~(I~-H)(/I~-CC~H~M~-~)(/~-PP~~)(C‘O)~(PM~~P~)(,~~-C~H~~~ ~WCo~(,r-,~‘-CEtCEt(‘EtCEt)(/~-~~~-CEtCEt)(COl,[P~OM~~~} I IW~lr(~r;~CC~,H~Me-~)(jr-CC~H~~~~~)~Cl)(CO):(PPh~)(~~‘-C~H~)~] lMoMCo(/i ~-S,(CO):(L)(I,‘-C~H~)~ [M = Fc. Ku. L = (S-PMePhPr: M = Ru. L = P(O~i~)-menth~lJI’I~~l ~Mo~eC’o(/~~-S)~/c-dppe)tCO~~,(~~~~CiH,~l~~~ IMFe(‘o(/cl-PM~)tCO),(l.i(~~i-L’)i (hl = klo. 1%‘L. = PPh:. PMe:Ptr. I.‘= (‘
Product Clustel

PtlOSrtilnE/PHOirHI

Metal Coordinating P-Donor Lipand

5

52

WATERMAN

by virtue

of a /L+apping

(CO)g($-L)] C5H.$iMej,

CUH7) have been reacted

derivatives

the specific

the bidentate

the cobalt

plant)

atoms

increases

not

on increasing

to afford

isolated

PCy;

the reaction

0

0

g derivatives

(3: I mixture

[ WCo,(/( between

(Fig.

and metallosclectivity

the ligand

d-cquatorially

The related

from

and biden-

I ). with

ligatin g at equatorial sites (with proposed to ligate at an axial site:

are diastereotopic,

to the phosphine

(/1-L)(CO)h(17~-C~Mes)].” was

P(OMe);

[MC(~~(/LI-CCO~P~‘)(CO)~(II’-C~M~~)]

unds dppe and arphos

and monodentate

products.‘“,‘“.‘”

and the bulky

atoms

[ MCo2(j~I-CR)

L = C;H5, C5H4Pr’,

although for most of the sites were not detined. NMR studies have clar-

and monodentate

the cobalt

9 clusters

CO? menthyl;

with phoaphites

cobalt-ligated

substitution

arphos

discrimination)

Similarly.

&group

of the (+)-menthylester-containin

to the MoCol

significantly, (no

to afford

the structures

respect

The group

(M = Mo, W; R = Me, Cc,H4Me-3,

tate phosphines ified

ligand.

et a/

cone angle

of diastereomers reacted

with

cobalt-ligated

obtained).

the bidentate

lig-

[ MC~$/L?-CCOJPI-‘)

3-CMc)(CO),(PHPhl) [ WCoz(/r

between

fl-om the phosphite

(,&CsH5)]

~-CMC)(CO)~(~~‘-C~H.~)I

0

0

(

(

(‘

c

“Very Mixed”-MetalCarbonyl Clusters

53

and PHPhZ. but is a presumed reaction intermediate en route to P-H activation (Section II.D.2.). The product of P-H cleavage in this case, namely [WCol(Il-H)(ln3-CC~,HJMe-4)(/1-PPh2)(CO)~,(~~’-C~H~)l, reacted with PMezPh to afford a Co-ligated product.‘” [ WCo:(ll-,I’-CEtCEtCEtCEt)(p-q-CEtCEt)(CO)s] reacted with P(OMe)j by displacement of carbonyl at the later transition metal.” Similarly, [W’Ir(pjCC~~H~Me-4)(~-CC~,H~Me-4)(CI)(CO)~(q-CgH5)2] reacted with PPh3 to afford an iridiun-ligated product, but the site of substitution was not determined.” The other trimetallic clusters to have been investigated are all chiral by virtue of four differing core constituents. The group 6-group &group 9 clusters [MFeCo(pjS)(CC))~($-C~HJR)] (M = MO. W: R = H, Me) have been reacted with monodentate and bidentate phosphines (Fig. Z).“.” The initial studies with these phosphines were undertaken with the goal of resolving the cluster enantiomers. A r-accmic mixture of clusters and the optically active phosphine (R)-PMePhPt afforded diastereomeric products which could be separated by crystallization. The phosphine was then removed by carbonylation to give the cluster enantiomers with an optical purity of%!-IOOcir~.‘” Reaction ofthe ruthenium-containing analogue [MoRLICO(/J~-S)(CO)~($-C~H~)] with optically active PMePhPr and P(Omcnthyl)Ph2 gave mixtures ofdinstcreoisomers [ M~RuCO(/QS)(CO)~(L)($ CjHj)] [L = (S)-PMePhPr. P(O-(-)-menthyl}Ph?]: in this case. the diastereoisomers could be separated chromatographically. but the pure enantiomers could not bc recovered. More recently. reaction of the (methylcyclopentadienyl )tungsteniron-cobalt example with dppc has been studied. In contrast to the monodentate phosphine derivative above, in which the phosphine ligates at the cobalt atom trur~.sto the Co-Fe vector, the bidentatc ligand bridges the Co-Fe linkage and coordinates ~UU~.Y to the Fe-MO and Co-S bonds. The related phosphinidene clusters [MFeCo(lr-PMe)(CO),(L)(?~~-CsH~)J (M = MO. W; L = PMe;Ph, PPh?) resulted from degradation of [MFeCol(/l?-PMe)(/l-AsMez)(CO)s(q-CjHi)] with the appropriate ligand: cobalt ligation was proposed on the basis of spectrlll data. but the substitution site was not ascertained.‘” The analogous [WFeCo(/l?PMc)(C0)7(L)($L’)] (L = PMe?, PMezPh: L’ = C5Hs. CSMe5) was formed by

54

WATERMAN et a/

reaction of [WFeCo(/17-PMe)(CO)s(,l~-L’)I with L. The reaction proceeded by way of an isolable adduct in which two equivalents of ligand have been added and two metal-metal bonds have been cleaved; heating the adduct in vacuum formed a closocluster product by elimination ofC0 and L.” Substitution at chiral alkylidyne clusters has also been demonstrated. The clusters [ MoCoNi(kr j-CR)(C0)5(t75C5H5)2] [R = Me. C(O)Ph] reacted with both PMe2PhZX and (R)-PMePhPr’” to afford cobalt-substituted derivatives, not unexpected as the other metal atoms are ligated by cyclopentadienyl groups: the incoming ligand was shown to be trur~~.v to the Co-C vector for the benzoyl-containing cluster (Fig. 3). Phosphine substitution at [MRuCo(H)(p~-CMe)(CO)s( $-CSH5)] (M = MO, W) surprisingly occurred at the group 8 metal rather than the group 9 metal to afford [MRuco(H)(/~jCMe)(CO),(L)($-C,H,)I (L = PMej, PMelPh. PMePhl, PPhl): the iron- and osmium-containing analogues were resistant to thermal CO substitution.3’1 The alkyl-coordinated clusters [MRuCo(y I-CR)(CO),( $CMe(CO:Me)NHC(O)Me} (I$C~H~)] (M = Mo, W; R = Me. Ph) reacted with both PPh? and CO by way of deinsertion ofacetamido acrylic acid methyl ester to form. in the case of phosphine. a ruthenium-ligated product.“’ cluster The dimolybdenum-dicobalt [Mo~C~~(/~~-S)(/~?-S)~(CO)~()IC5H4Me)2]. which desulfurized organic thiols (Section lI.D.2.). reacted with phos” J7 Kinetic studies showed that reaction phines by ligand substitution at cobalt.--. proceeded by two elementary steps: initial formation of an adduct followed by loss ofC0 (Fig. 4). The extent of substitution is dominated by electronic considerations; while phosphine substitution proceeded to give bis-substituted derivatives. reaction with isocyanides afforded tris-substituted products (see Section II.B.2.). These substitution reactions proceeded at room temperature: heating the PHzPh-substituted product led to double P-H bond cleavage and coordination of PJ-phosphinidene (Section II.D.2.). The same cluster reacted with bidentate phosphines to afford cobalt-chelated products (Fig. 5). with excess dmpe affording a bis-substituted derivative.3’ In contrast. the related cluster [Mo2C02(~~-S)~(CO)1(11”-C5H4Me)21

“Very Mixed”-Metal

I/ .111\

FIG. 3.

Monodentate

Carbonyl Clusters

55

iI\

P-donor- ligand substitution

at IM~~C~~(~~J-S)(,~,-S)~(CO)?(,~~-C~H,M~)~~:

(i) L= P(OM~)J. PH2Ph. PHPh:. PBu:. PP~I. PMel. (ii) L= P(OMe)l. PHPh2.

rcacted with dppe to form a product in which the bidentate ligand is believed to span the Co-Co vector. and in the presence of excess dppe afforded D polymeric product. but the products were incompletely characterized.jj The tungsten-triiridium cluster [WIr-JCO), ,(~$C~HS)] and its molyhdenum analogue have also been extensively investigated (Fig. 6). Reaction of

56

WATERMAN

[ Wlr$C0)1

1(11~-C5Hg)] with

ature in a stepwise ligated

derivatives

ofwhich phites

as mixtures

were ascertained reacted

containing greater

mixtures steric

isostructural

phosphincs

the mono-.

ofinterconvcrting

to atl‘ord

mixtures

constraints;

only

with

of

varying

mono-

in solution,

and

q5-CjH5)] extent

at iridium

to afford

niono-

temper-

. icnctccl were

Phos-

The 4d metaland

reacted

and his-substituted

the identitie\

with

of’ substitution.

his-substitution

iridiuin-

studies.“.‘s

products.“’

;~n;~logo~~s

[ M~~I~~(/~I-CO)(/I-CO)(CO),(/~~-C~H~)~~

tate phosphines

at room

and spectroscopic

[ Molr~(/~-CO)$CO)x(

ol~clusters

proceeded

his-, and tria-suhatituted ihomers

by crystallographic

similarly

homologue

affording

monodentatc to afford

manner

et al.

less control, reacted with

ohserved.” with

The

monoden-

products.“’

Hiden-

tate phosphines reacted with [WIr3(CO)I I(~&CiHi)] at iridium to aftord diaxially ligated edge-bridged products, an unexpected result with the linear diphosphine dppa. [ W2Pt2(/1 ;-CC~HIMe-4)(/L-CC~,H,Mc-4)(CO)~( to’-cod)( I~‘-C~H~)~] reacted with

PMePh-

to allord and

the

at platinum

by displacement

of the “lightly

stabilizing”

cod ligand

[WIPt2(/13-CC,HJMe-4)(~-CC~,HJMe-3)(CO)~(PMePh~)~(~~.i-C~H,i)~I.~’ ruthenium-ligated

product

(Fig.

7)

IW2RuPt(El;-CC~,H~Mc-4)(/1-CC,,H~Me--1)(C0)7(,li-C~H5)1l clusters IMFeCo,(Il?-E)(/L-AsMe2)(CO)x(tj’-CgHj)]

was

obtained

on

reaction

of

with PMezPh.““Thc (M = MO, W: E = S. PMe)

“Very Mixed”-Metal

reacted ucts;

with

donor

the only

ligated even

ligands

products

RNC,

were

phosphine

accompanied could

to afford

core

but reaction being

ligands with obtained

degradation

nuclearity

were

The vast majority at

coordinated

(Section

nuclearity

W)

contain

be expected

to undergo

was somewhat

complex.

II.E.2.).JX

facile with

metals.

or acetylene

prod-

the cobalt8). although

products,‘”

by CO. The chain

and

complexes

“lightly

atnbilizing”

ligand

substitution.

core-expanded

prod-

”

ofphosphine/phosphite-substituted

late transition CO

(Fig. lower

replaced

(M = Cr. MO,

and might

phosphines

by other

be readily

[ M2Pt(CO)(,(NCPh)$rI”-CSHs)~] benzonitrile

ligation

~lnd PRj

the cluster

1MFeCo2(/l.i-PMe)(~-AsMel)(C0)7(PPIlI)(,15-C~Hs)] these clusters

the incoming

ucts

P(OR)3

to retain

57

Carbonyl Clusters

In contrast.

phosphite

products ligands

in [ RePtj(/L-dppnl)i(CO)3(L)]4

PPh 3 * (‘0

involve displaced .J2 which

Y-ligand rheniumxc

the

58

WATERMAN et al.

MC2’//w,

c

(’

/?I’\

\,

,

Y’

I p’\w/p’

(‘

p’\J

(‘

I”\Jpt

Mc \

-

‘1

MC

addition ylene

products adducts

the more

from reaction

were formed

electron-rich

at rhenium,

rather

tion studies

on larger

the formation CsH&] from

oL‘ L with [RePt3(~1-dppt~,)3(CO)~]‘.

as the starting

cluster

[RePt3(~13-0)2(~~-dppm)7(C0)3]i

than addition, “very

on reaction

mixed”-metal

with

clusters

The CO/acct-

is comparatively

electron

underwent phosphite.“,”

poor;

substitution

Ligand

substitu-

arc very rare. one example

being

of [M(~2W.iPth(/*3-CChHJMe-4)?(/13-CMe)J(CO)Io(PMe,Ph)1(,7sdisplacement of the weakly-bound cod ligands in [MoZW3Pt&li-

CC~,H~Me-4)~(~~~-CMe)~(CO)lo(~~“-cod)~(~~5-C5H5)5] by PMelPh (Fig. 9).“”

“Very Mixed”-Metal

Almost sition

all other examples

metal

honylation

and involved of clusters

also replace

FK;. IO.

[Mn2P~(CO),21.

of Ii&and

replacement

the introduction

occurs

phosphines

easily

under

have occurred

or replacement

with

some

readily

displaced

circumstances:

proceeded

to

stream after

ofC0

passed

2 h the latter

Nitriles

and dienes

clusters;

through cluster

carbonylation [MozCo$/~j-

in a facile

a solution

of the cluster affording

are ‘*lightly

not surprisingly. fashion

stabilizing”

reaction

to afford

the

ligand

akstance

a halide

ligands

[MnzPt(CO)I1]

ligand

(a alou

(Fig.

acceptor

I ()).>j

and

I I).”

in the precursor

the ~l’-cotl by carbonyls replacement W)

to give

In the tungsten-containing and the terminal

carbonyl

CO proceeded

(M = Mo.

proceeding

however, products.‘”

metal

with

In contrast.

(TI[PF(,]).

cluster

at transition

was displaced

C0)~(~~-dppm)2(CO)(-dppm)20(,~‘-CsHi)I ’ (Fig. pies, both the chloro

product

conditions

for a few minutes);

at ~MPd~(~~~-CO)~(/~-dpp~~i)~Cl(~~~-CiH5)1 of

substitution

mild

trinuclear

[CrlRh(~ri-S)1(/1-SBu’)(C0),(1/5-C~H5)~1.’~

chloro

the

of [Mn2Pt(CO)lo(NCPh)2]

in [Cr2Rh(/l:-S)2(~r-SBu’)(?~~-cod)(?~~-Cg] ford

of IWFeCo2(lli-PMe)(ln-

under

had degraded

II). Car-

but CO can

afforded afford

I WFeCo7(/13-PMe)(y-AsMe2)(CO)x(l7’-C5fI~)l

ligands,

for example.

and carbonylation

AsMel)(C0)7(PPh;)(175-CjHj)1

at the late tran-

of CO (Table

of [ Mo2Co7(E1i-PPh)(/I;-S)3(CO)(PH2Ph)(,I’-C5H~Me),I PPh)(/r3-S)3(CO),(,Is-C~H,Me)~],~~

59

Carbonyl Clusters

carhonyl

ligand to

af-

of the required

lMPd2(/13cxanligand

in

1+

CO t ‘1-1I PF, I

II

Pt Rh Pd I’d Pd co CO CO

co - KKC

CO co

PPhj - CO PH:Ph - C‘O PhCN - CO ,I’-cod i 2CO (‘I- + co co - BrCl - BI KO - 2cp CO - RNC‘

KO

+ 2co co 3(‘0

2PllC~Pll - 2x + 2cI - 30

2co - s 2co - Pl1C:H ZCO ---f diw ?CO - Mc:SiC~SiMc~ 7(Y) - McC2Me

cp - 1. (L = CH3(‘02. Cl I

TABLE

“Very Mixed”-Metal

FK;. Bu’.

(ii)

I?.

Iwnitrile

athtitution

ZRNC. R = Bu’.

(iii)

Carbonyl Clusters

61

at [Mo~CO~(/LJ-S)(/~ ~-S)~(CO),(,,‘-(‘~~-l,~l~)~~: (I) RNC. R = Mc. 3RNC. R = Me. Bu’.

the product can be displaced by bromide. Metal exchange procedures to form “very mixed”-metal clusters (Section [I.E. I .) have utilized [Ni($-CgHs)?] and [ Ni(CO)(&CSH5)12 as sources of “Ni($-CsH5).” but the former also delivers the cyclopentadienyl group which can displace carbonyl ligands: reaction of [MoCo7(/1#ZCO?Pr’)(CO)x(ll’-C5H)1 witheither [Ni($-CgH5)2] orthemore logical cyclopentadiene afforded [ MoCo~(~~3-CC07Pri)(~~-CO)(CO)~(~~s-C5Hj)~].s’ The carbonyl ligands in IMo2C~~2(~J-S)(,~i-S)2(CO)-I(~~s-CgH~Me),] and [ MoZCoZ(LLJ-S)J(CO)l( qs-CjHJMe)21 can be displaced by isocyanicles,J7~‘7~‘X though reaction of the former only proceeded to form the tris-substituted product (Figs. 12, 13). Both clusters desulfurized isothiocyanates, with the resultant isocyanides forming substitution products.“x Carbonyl sulfide can be used as a source of sulfide ligands. Thus. reaction of [Mo$Zo&L~-S)(~~-S)?(CO)~(qs-CsH,Me)Z] with COS afforded (Mo?CO$/I~-S)J (C0)2($-CSHIMe)~J. a process which can be reversed upon carbonylation (Fig. l4).5x The same cluster added one equivalent of phenylacetylene in a /A?-$fashion across a MoCol face with loss of two CO ligands and rearrangement of the /LA-sulfdo ligand into a pi-coordination mode.“” The tetrahedral cluster [WIr7(CO)I ~(I$-CSH~)], in contrast, added two equivalents of diphenylacctylene, one at a heterometallic Wlr-, face, and the other at the unique homometallic Ir: face.“’ Studies of phosphine and phosphite substitution at (WCO~(/~-CC~,HJM~4)(CO)s(q’-L)] (L = C5H5, C5H3SiMe3) summarized in Section I1.B. 1. have been extended to embrace diars and (for L=CSH5) Me$iCECSiMei.‘” For diars, a cobalt-ligated product was obtained, but the specific substitution sites were not ascertained. whereas the alkyne was shown to coordinate in a /L-$fashion across

62

WATERMAN et a/

a W-Co linkage. But-2-yne replacement of two CO ligands at [WFeRh(/l,\CR)(/I-CO)(CO),;(HB(~~)~}(~~~-C~H~)~ (R = Me. C~,HJM~-~) occurred to al‘ford ;I /I-$l-ligating internal acetylene bridging the W-Rh bond.“’ The II’-coordinated edge-bridging cyclopentadicnyl ligmd in [MoPd7(lrj-CO)(/1-ll~-CSH,)(,~CO)z(PR~)?(lj-C5Hs)l (R= Pr’. Et) was replaced on reaction with CHICOIH or SiClMe;. affording [MoPdl(/li-CO)(,L-CO)7(/1-L)(PR)2(,7j-CH~)l (L= CHICO1, Cl).“’ Other reports of ligand replacement at “very mixed”-metal clusters involve ;I Ihrnmal oxidation state change. Reaction of 1Mo$?o$/l 1-S)4(CO)2(q5-CiHJEt)2] with halogens or diphenyl disulfide afforded [ Mo2Col(/~ 3-S)4(X)7( I~‘-C~H~E~)~] (X = Cl. Br, I, SPh),“3.“1 with a formal oxidation at the cobalt atoms, and clcavage of the Co-Co linkage (Fig. IS). All product clusters are paramagnetic in the solid state (but less so in solution), wnith higher spin states disfavored as the

“Very Mixed”-Metal

Carbonyl Clusters

63

x, x = I. (‘I

r-donor ability ofX increases. Oxidation at the late transition metal was also seen upon heating [MoRh3(/13-AsRh(CO)(I75-CsH~)](~~-CO)~(~~~-C~Hs)~] in CHCl+ with the “action” occurring at the non-cluster rhodium atom (Fig. 16).“5 In contrast, the earlier transition metal was oxidized in ;1 stepwise fashion upon reacting [RePt3(lr-dppm)3(CO)j]+ with molecular oxygen, with (overall) a formal increase of+6 in oxidation state (Fig. 17).“” The oxidation product isolated was sensitive to the reaction conditions, with hydrogen peroxide or molecular oxygen/photolysis affording products lacking metal-metal bonds.“7

I’ J

RI1

WATERMAN

64

et a/

C. Ligand Addition A range ofelectrophiles ligand

displacement,

have been added to “very

and thcsc are summarized

the reactions

of clusters

with nucleophiles

is frequently

arbitrary,

though,

latter. The examples which

the formal

electron

count

cluster

addition

at “very

reactions reactions

as ligand

the former

of the latter collected

by compensating The

with

bond

mixed”-metal

in this section. substitution

often

on the cluster

mixed”-rnctal

sometimes

111 collects

of (W2Pt(,-I-PPh2)2(CO)5(,75-CHS)LI

with

[ Au(PPhJ)]

HBFJ

afforded

with

adducts

the electrophile

ing stereochemistry

with

bond.

afforded

(Fig.

whereas

HCI

respect

lX).““Theclusteranion

reacted linkage.“’

with

HBFJ

Protonation

by

been

contrasted;

bridging

a W-Pt

to the bridging

a product

accompanied

examples

with

groups

a terminal

two and

of‘ ligand

sources

of Ht.

[ Au(PPhj)]PF(,

linkage.

but with

dil’fer-

across

the other

W-Pt

Pt-bound

hydrido

ligand

[MoCo2(/1~-CC~,H1Me-4)(/r-PPh2)(CO)(,(r75-CjHs)]~ across the heterornetallic addition of H

at the related

of the

to those in

clusters.

and the isolobal

’ , have

01

addition

by way

are restricted

increases,

Table

without

or ligand

proceeding

in this section

cleavage(s).

clusters

The classification

1WCo,(IL-H)(II~-CMe)(ll-PPh2)(CO)h(lli-

MO-Co

66

WATERMAN

CsH5)] age.

was shown

but

stable

by ‘H NMR

the product

adding

at the only

lar cluster

anion to afford

;1 variety

of bases,

acy

pentanuclear

the reaction

the reverse

with

methoxidc

derivative.7’

occurred

Most

linkage.

hydrido

Mo-MO

bond to afford

the butterfly

PBu’C~,H~-2-PBu’)(CO)(,()li-C~Hg)21;

bridging

mentioned

in Section

S)~(CO)4(~$C5H~Me)~] ing Co-S

either

past

the ad~tuct.‘~

The

by way ofan 57 although

unsaturated

cluster

PPh,)2(y-CO)(CO)~(II’-CSHi)ll.

with

molecule

rhodium

of CO

at the terminal

adduct

Ihrmal group

by P-C

Llnsaturation.“.“’ 9 clusters

bond

formal

has been the subject

CO)~(C0)7(,~5-CjHi)ll RCIR’)(,~-CO)l(CO)l( I,4’-Cr,H,C-CChH~N02.

reacted qS-CjH+j CH?Br),

with acompensat-

reaction

of several

double

to afford

did not proceed

bonds.

[ W2Rhl(/~

added

one

3-CMe)(/l-

I~).Theproductsubscqucntly

eliminated

chemistry

with

at cobalt.

W=Rh

atom

(Fig.

The acetylene

to react.”

IW~Rhl(/(3-CMe)(/~-CMeC(0)}(/L-

and then

formation,

cluster by cleav-

at [ Mo~CO~(/L~-S)(/L~-

for PMel

CMeC(0)}(~n-PPhl)2(EI-CO)(CO)I(,15-CiH5)~I isomerized

the Mn-Pt

the isostructural

failed

substitution

(Fig. 4).”

this. proba-

[ MolCo2(/l.r-ll~-NO)(,~~-,,~-

the same conditions,

I1.B. I . ligand

occurred

bond cleavage

isomers,

to the tetrahedral

[ MoCoi(~~:-~~‘-PBu’C~,H~-2-PBu’)(,r-CO)(C0)~(r~”-CjHS)] As

chemwith

proceeded

cluster

under

with

addition

two

[Mo2Col(/li-,l’-PBu’C~~H~-2-PB~,’)(,~-CO)(CO)~,(~li-CgH5)1j age ofthe

stoichiometric proceeded

Consistent

to give

01‘ NOBFJ

triangu-

via the intermedi-

linkage.

ligund

” Addition

[Re4Pt(jrelectrophile

spiked

with

reaction

01‘ the electrophile occurred

to the incoming Re-Pt

The

proceeding

at the heterometallic

of [MnRe2Pt(I(-H)2(CO)l_II~

cluster

the incoming

linkage.”

link’ is un-

hc protonated

can

[ReTPt(LL-H);(CO),J\:

corresponding

(W-Co)

“bow-tie” with

Re-Pt

[Re3Pt(p-H)2(CO)14]

or the unbridged

at a heterometallic

reversibly,

non-hydrido-bridged

has therefore

protonation

The

he protonated

of a carbomethoxy

istry bly

of HBF1.‘”

can also

CFjSOjH

to also occur

IWCo2(lr-H)2(,li-CMe)(EI-PPh~)(CO)(,(,15-C~Hi)]

in the absence

H)5(CO)lh]-

et al.

CO to regenerate

of tetrahedral

mixed

the

g~-oul~ 6-G

studies.

acetylenes

For example, IMo21r2(/1afford IMoZlrZ(,lJ-q’ to

(R = R’ = Ph. H: R = H. R’ = Ph. 4ChH4N02. with

a butterfly

metal

core

gcomctry

h-med

“Very Mixed”-Metal by Mo-Mo pleting

cleavage.

a Mo11r&Y2

and the acetylene

octahedron:

trends acetylene

> terminal

phenylacctylenc.

ascribed

The

related

clusters reacted

ilarly

/IJ-$alkyne

reaction

between

contrast.

> internal

acctylcncs

of steric

and

and

to afford

occupying

to the II-Ir

of reaction

;I butterfly

rcactcd

Wlr?

] W~CO~(,~-CO)~(CO)~(~~~_

clcfi

products, was

and ;I sin-

obtained

diphenylncetylene

with

studies

eft’ccts.“’

from

the

to ai‘ford

In

the acetylenes

ifrrc~/-

face-capping

the

ll.B.2.).“’

faces (Section

of’ reactivity

the

and l~henylacctylcnc.7”

with

c//irl ] WIr3(/(.;-,I’-PhC7Ph)7(CO),(,I-CjHj)] II-1 and one of’the

con>

electronic

analogous

]MoCo~(,K0)3(CO)x(rl’-C5H4Me)] I(I$-C,H~)]

vector

rates revealed

alkyneand4nitrophenylacetylenc

to ;I combination

with

] WIrq(CO)I

A number

parallel

analysis

[W21r2(CO)Io(~&H5)~]7X

C5H4Me)2]7h ligated

lying

qualitative

alkyne

67

Carbonyl Clusters

of the coordinatively

unsaturated

(51 e) clusters

]RcPt3(/1-dppm)~(CO)~]~ and ( RcPt;(EI-df’p”i);(0)~]~t. in which the apical rhcni~1111s differ by 6 in I’ormal oxidation state. have been reported. The cluster ] RePtI( ~cdppm);(O)l]+

(itself

\,i;l the addition more

reactive rhenium

(Fig.

by reaction

of’ ]RePtj(/r-clpl.“ii);(CO);]

[RePt;(/~;-0)2(/r-dppm)3(CO);]

to ligand

~lppm)~(CO)~]-~. the

formed

product

addition

than

’ rcactcd

20).4’~‘“~“”

and

Cluster

with

halide

ions

with

by

]RePt3(~~-dppm)3(0),]

‘~ similarly

II.B.3.)

analogue neutral

capping

’ with

Section

its carhonyl-ligated

] RcPtj(lc-dpl)“l)j(CO)c] atom.

’ “:

] RePt:(/l-

donor

the

ligands

wirh

at

lltce

triplatinum

rcactcd

OZ.

was

halides.

and \vith Hg. Tl(acac). and SnX3 . by capping the triplatinum f’xe. ~LI( carbonylation also occurred at the triplatinum face. and reaction with phosphitc occurred at platinum. dation

the latter

two

state” analogue

both

(Fig.

contrastin

2(I).“’ +

g with

the chemistry

The related

cluster

at the “low

cation

] RePt3(/l

oxi-

:-0),(/1-

~~pp”‘h(CO)iI+, the lrioxo

intermediate in the transf’orntation of tricnrbonyl cluster to (see above), reacted with phosphitcs to afford ] RcPt$/l 3-0)2(/(-

cluster

dppm)~(CO),( logucs. rather

P(OR)j)

the more

]+ (R = Me. Ph):.“,”

electron

than the addition

D. Ligand Metal of ways.

unlike

rich dicarbonyl-dioxc, products

(Section

the tricarbonyl

cluster

afforded

or trioxo

;m;l-

the sllbstitution

1I.B. I .).

Transformations

clusters many

have been shown of which

more

metal

atoms

clf‘ect

bond

cleavage

to transform

are not possible

in specific

geometric

and formation

organic

\ubstratea

at monometallic relationships

and stabilize

in a large numba .I4 two OI

complexes; are Krcquently

the resulting

required

ligand

to

iragments.

The bond polarity in mixed-metal clusters which may enhance substrate activation should be maxitnized in progressing to “very mixed”-metal systems. For example. coupling oxophilic and carbophilic metals should facilitate C-heteroatom cleavage heteroatom

linkages,

but this

together in a “very mixed”-metal by formation of strong M-C

is one area that has been

little

exploited.

cluster and MLigand

L

I-

Ph~t

PI, .P

“Very Mixed”-Metal

69

Carbonyl Clusters

hlc

1'

Me

I

(‘

(

PI

transformations ifications

ligands

Transformations of C-H

bond

ters have

ligands

at C-donor

appeared.

arc summarized

ligands

or C-H

Protonation

carbon.

formation utilized into

occurring

nated vinylidene

;I a-alkyl

linkage

Thus ployed

by formal (Fig.

at a single

face,

at a M-M

ultimately

deficiency

but the reverse

at tungsten

24);

insertion unlike

alkyne,

The remaining

of an alkene

by

examples

in this

section,

of C-C

alone

activation

or in concert

and/or

with

C-C

cluster-bound

of C-H

bond

to form

the “action”

formation alkylidyne

(‘H,K c

M’

the reaction

metal.3’

either

7-

the easier. The coordi-

example

into an Ru-H

(‘ H

\:/

but at the

relieved

appears

/13-?/‘-ligated

23).‘5.x6

other

reaction

R

,,,‘-

clus-

bond,

occurred

faces (Fig. 22).“5

by thermolyzing

I ,2-H shift (Fig.

far, all examples alkynes,

protonation

range ofheterotrimetallic

can be formed

occurred

occurred

wider

by ;I formal

formation

occurs

examples

mixed”-metal

(Fig. 2 I ).s’ Otherexamples ofC-H formation have vinylidene can be converted source.XS.Xh Coordinated

at a trimetallic

at a much

proceeding

IV. Several

at “very

clusters

electron

mod-

linkage

Hz as the hydrogen

alkylidyne

in Table

formation

at most

1I.D. I ., while

II.D.2.

are collected

bond

with the consequent

of an $-aryl

in Section

in Section

in [WRePt(/AXZ6HIMe-4)(CO)U(PMe;),] Akylidyne

I’MC, I’\le :

are reviewed

activation

H

I:t,O - s

PMC,

at C-donor

of other

HRF,

PMC;

(1)

,,$ -

-

Iv’-

(ii)

\/

-M”(

have

en-

or CO.

72

WATERMAN

Phenylvinylidene

was

dimerized

et al.

in a head-to-head

[RelNiz(El-r-112-C=CHPh)(~~-CO)(CO)(,(Ii’-CgHs)21. atoms

in

the

wing-tip

positions:“’

CHPh)(CO)6($CgH5)z] tip positions.

dicobalt-dimolybdenum ceeding action

addition

of excess internal proceeded

fly cluster

units. The major ing from

product

insertion

W-h

has the potential

one CpW(CO)? cluster

which

reacted

two cluster-bound age

with

products

Reactions bridging

cluster

excess

acetylenes,

two alkylidyne could

of alkynes

as C-C

ligands with ligands

in the wing-

face of a sulfur-rich

fashion.

the reaction

prorc-

ditungsten-diiridium

formation.

to afford

a butter-

ally1 and alkylidyne

a mono-acetylene

adduct

result-

1I.C.). which could not be converted in core con(Fig. 26). “.” Modification

affect Ir(CO)j

product

selection.

fragment

afforded

of the same acetylene

and ;I butterfly

cluster

and a dimer

not be interconverted

alkylidyne

nickel

bond (Section

an isolohal

with

atoms

with cluster-bound was

with

(Fig. 25).“” In contrast,

at a tetrahedral

as well

to dramatically

unit with

rhenium

molecules

of the same reaction

into a W-W

to the allyI(alkylidyne)-containing position

with

PhCSCPh

thermolyzing

IRe2Ni,(~~~-l/‘-PhC=CCH=

in a had-to-head

cleavage)

on cluster

across a Co?Mo

acetylene

cleavage

from

cluster

also

ofthe

acetylene

by C-C

(resulting

product

was dimerized

cluster,

by stepwise

cluster

the

is a butterfly

Phenylacetylene

manner a butterfly

(Fig.

trinucleul proceeded

to afford

resulting

frorn

of diphenylacetylene:

27).“’ group h-group by

Thus.

coupling

9 clusters the

replacing

an isostructural

a product Ir-lr

with cleav-

again.

these

incorporating

C’-donor

ligands.

“Very Mixed”-Metal

Carbonyl Clusters

73

Diphenylacetylene and Shexyne reacted with [MolCo(/l3-CH)(C0),(175-C5Hj)71 to afford chain-lengthened organic ligands with allylic ligation, but whereas the former also gave a product resulting from PhCrCPh cleavage and C-C bond formation, the latter gave a product from coupling the ally1 unit with CO (Fig. 2X).‘* 2-Butyne and Shexyne reacted in a similar fashion at tungsten-dicobalt alkylidyne clusters as at the dimolybdenum-cobalt cluster above; coupling of acetylene. CChHJMe-4, and CO gave a WCo?-supported CJ fragment, although the presence of bridging phosphido led to a side reaction involving P-C formation (Fig. 29).‘” Alkylidyne groups have hecn cleaved, as well as coupled, when a sufficiently reactive substituent is present; reaction of [MCol(lrl-CCOZEt,(C0)x(,75CIHJMe)] (M = MO, W) with IFe(CO)j]‘p/Ht afforded [MCO&Qq’-CCO) (,I-CO)(CO),(~~~-C~H~M~)I by cleavage of the ethoxy group, in addition to

74

the

expected

metal-exchange

[Co~(p?-CCI)(CO)g]

underwent

WATERMAN

et a/

product.

The

C-Cl

[MoCo2(~-13-CH)(CO)x(r15-C5Hs)l. ‘)h Alkyldiazocarboxylates

reacted

with

age and coordination

of the resultant

one CHCOlR

bridges

bridging atom

ligand

a W-Ir

(Fig.

an Ir-lr

This

product

could

chloromethylidyne

bond,

Ii&and

as well as metal exchange

[ W,lr~(CO)l,~(

carbene

bond and the estercarbonyl

30).““~“’

“’

cleavage

units while

q5-CgH5)1] in two distinct the other

coordinating not be obtained

by C-N

clcav-

environments;

caps ;I W?Ir

to the oxophilic by C-C

in

to afford

face by tungsten

cleavage:

both

“Very Mixed”-MetalCarbonyl Clusters

75

reaction of [ W21r2(CO)to( $-CjHj)l] with RO$ZCH=CHCO,R, and attempted hydrogenation of [W71r2(/1J-rl~-Et02CC~COIEt)(CO)xl. were unsuccessful. Solvent dichlorornethane has been activated; reaction with [ M~Q~(/LJ-S)(/L ~-S)?(/L;CO)(I/‘-dmpe)l(,l’-C~H~Me)~l proceeded by C-H and double C-Cl activation to afford the methylidyne-containing cluster 1M~~C~Q(,L;-CH)(p i-S);(112-tlmpe)2(,1iCSHJMe)2]im.3’ The examples above involve the cluster mediating the transformation of organic substrates and stabilizing the resultant residues by coordination. Several clustercoordinated functionalizedcyclopentadienyl groups have also been modified while maintaining their qs-ligation. For example. the cyclopentadienyl substituents in IMoFeCo(E13-S)(CO)~(~~~-CSH1R)l [R = CHO, C(O)Me], [ (MF~C~(/L~-S)(CO)~ (,~T-C~H~)]I(~~-C(0)-4-C~~H~C(O)]~ (M = Mo. W), [MoR~Co(/l-Sc)(CO)~(lljCsH4C(0)Me] 1, and [MFeNi(,L3-S)(CO)S(,15-CiHj)(175-CjH~C(0)R}l (M = Mo. W; R = H. Me) wet-e reduced by N~BHJ to alf‘ord [MoFeCo(,n3-S)(CO)X(l,‘C,H,R’)j [R’ = CH20H. CH(OH)Me]. [ (MFeCo(EI;-S)(CO)x(,l’-CiH1)]l

KO

76

WATERMAN

et al.

(p-CH(OH)-4-C,H.$.IHOH] 1. [ MoRuCo( /I~-SC)(CO)~( II’-CSHJCHMeOH}]. and [ MFeNi(/l;-S)(C0)5(17’-CjH5)( &Y~H&HROH)]. respectively:“‘~“’ the secondary alcohol derivatives [ MFeNi(~~~-S)(CO)5(~~5-CsHs)(r$CsH~CHMeOH)] were then alkylated by Et,OBF, to afford ether derivatives [ MFeNi(~r3-S)(CO)s(qsCsHj)( $-CsHJCH(OEt)Me]j.“’ The ketone functional group in [ MFeNi(/r;S)(CO)~($C~HS)( $‘-CSH~C(O)M~) 1 (M = Mo, W) reacted with 2.4-dinitrophenylhydrazine to afford the expected phcnylhydrazone derivatives [ MFcNi (~~~-S)(C0)s(~‘-C~Hs)~~~~-CjHJC(Me)=NNH-2,4-C~,H(N02,2)].”’

Very few reports concerning transformations of ligands with other donor atoms exist (Table V). P-H activation at secondary phosphines is the most common motif. with the metal-metal bonds at the heterometallic facts stabilizing the resulting fragments in each case (Figs. 3 I, 32. 33).“‘.7”.“7 In the formation of both

PHPh-.

Ph, I’ MC------

P-H d~ation: PHPh: i PPh2 + H P-H activation: PHPhz + PPh2 + H P-H activation: PHR?+PR2+H(R=Et.Ph) P-H activation: PH2Ph - PPh + HI P-C. C-H activation. C-H fotmution: PPhj + PPhC6H4-2 + CoHh Ar-S activation: Ar-S + Ar + S S-R. S-H activation: RSH+ S+KH P-C. C-H formation: PPh2 + H + RC-CR i PPh$(,i\-CR=C‘HR) C-C activation. P-C formation (‘RlcCO i PPh; 4 (‘hlcPPhl + CO

IWCol{p I-C(C~,H~M~-~)CRCRCO](I,CO)(CO),(PPhz(~~i,-CR=CHR)}(~,‘-CjHi )I (R = Ms. Er) [W;R~~(/~~-CM~)(/~-CM~~(/I~CM~PP~~)(~~-CO)~(~~I’Fh2)(COil(ij”-C,I ii);]

Co-Co

bond\/Mo~Co

bond,

MO-CO hondq

Ir; face

Mo(‘o? fact

MO-Pt bond\/.Mo- Pt. Pt-PI bond\

Mo-Co.

Face/Bond/Metal Coordinating Tran\formed Ligand

x2. 102

20

s2

100. IOI

99

52.98

20

97

70

Ref.

78

WATERMAN

et a/

[ MoCol(,l-H)(En7-CC~,H,Mc-4)(~~-PPhl)(CO)(,(,li-C’iH~)17” PR:)$CO)s(

I]-CSHS)I

tion metal was observed double

P-H

More coordinated [ WIr3(CO), tion. (Fig. ,crs..

:i

and

l.,(PPh~),(117-C5Hs)l suggests

coordination (Fig.

36). At higher

rircd

a range

in propylene of propene:

the product

dpp~n)~(CO)j(S)]~ Examples

were

of “very

arc still I-arc. with

at mixed

[ RePt?(/r

fuels.

for

the

At low ternpcriitures.

but OII warming bond (Fig.

CILIS-

acti\,e

the thiophe-

cvcntually

clen\cd

cluster

rlesulf~~-

37). The C-S

;-S)~(lc-dppm):(CO);]

with

bonds

m)lution

’ and [ RePt;(/l-

residues.““.“‘”

cluster-assisted extant

product

conditions

iiiolybdcnum-cob~~lt

and the C-S compounds

in this sec-

the reaction

combination

of liquid at a cobalt.

of heating

I;ICC. The

by [RePt~(/I-dpl~iii)j(CO):It

the sulfide

literature

under

;I metal

organic

mixed”-metal

both

cleaved

on

examplcs

the same molybdenLlm-cobnlt

cleaved

clusters

contained

observed

other

contain

linkage

of sulfLlr-cont3iniil~ sultide

unlike

14).51.0t;

Orthornetallation

was

reported

occurrcd

temperatures,

(Fig.

at the homometallic

hydrodesulfurir.~ition

a heterometallic

Not surprisingly.

cleavage.

cleaugc.

benzene

(x = I-3):‘)‘)

is coordinated

of thiophenoxide

bridged

of

that the M-P bond wa

important

and

(WCO$/l-

at the later tranai-

is also possible

of C-hctcroatom

elimination

residue

of‘phosphine

activation

phosphines

35). C-S cleavage has been 5'-..5s (77 hX.I0I1.101.l0~.11~-1 which

industrially noxide

P-H

at primary

are examples

PPh;

the ligated

distribution

to precede

activation

interesting

Lllld

(R = Et. Ph).‘” coordination

C-hctcroatom

bond formation

exan~plcs

phosphido ligund with ;I C-ligand. Phosphido. bled stercospecilically to afford PPh:((.i.\-CR=CHR)

involving coupling and alkyne hydrido. (Fig. 29),“’

while

of bridging were asscnan unusual

“Very Mixed”-MetalCarbonyl Clusters

79

isomcrization replaced the bridging phosphido at a W-Rh linkage with a bridging carbonyl. affording the PhlP=CMe ligand (Fig. 3X).‘“’ E. Core Transformations The premise of this review is that synthetic procedures for “very mixed”-metal clusters are comparatively well understood, but that reactivity and physical properties are less well studied. Metal core transformations (modifications of a preexisting cluster) fall into both the synthesis and reactivity categories. A summary is presented here, but as they have been reviewed elsewhere (see Refs. 4, lO7-109), the account below is necessarily brief. Section 1I.E.I. considers core transformations where the cluster core nuclearity is preserved. whereas Section II.E.2. summarizes reactions involving a change in core sire. I Mettrl t::rchrru,Ly Efficient routes into “very mixed”-metal clusters by metal exchange reactions have been developed, principally by Vahrenkamp and co-workers. Metal exchange

80

WATERMAN

et al.

“Very Mixed”-Metal reactions

are those

replaced same

in which

by a different

total

number

of metal

bc expected

to be quite

with

occurring

others

systematic

or more group

atoms.

complex,

of a cluster

exchange

proceed

reactions

reactions

units.’ Specific

the heterometal

vertices

are

containing

by one-step

and substitution

oforganometallic

to introduce

groups

a new cluster

metal

reactions

addition

and incorporation

have been utilized

metal-ligand to afford

Although

many

by multistep

addition

reagents

one

metal-ligand

81

Carbonyl Clusters

the could

processes, involving classes ot

by metal exchange

reactions: A. Metal R. Metal

carbonyl anionskyclopentadienylmetal carbonyls/cyclopentadienylmetal

carbonyl anions carbonyls/nickclocene/

IPt(r72-C2H~)(PPh2)21 C. Cyclopentadienylmctal

carbonyl

arsenides

D. Cyclopentadienylmetal

carbonyl

hydrides/chlorides

Lund Table of reagents routes The

a classification

by each reaction

have been by far the most popular:

are considerably

the group utilired

VI contains

6 metals.

trinuclear

more

limited

The arsenide clusters

in the “very

in scope,

with

exchange

and hydride/chloride

examples

route has been defined

[CO~(/L~-CR)(CO),~]

mixed”-metal

type. The first two classes

the arsenide

thus far confined

mechanistically

arc the most reactions

common

reported

to 39).

precursors

thus far (Fig. 40),

s

M = MO. M

-(‘(I

(Fig.

(‘0

82

83

$

(M = Mo. W)

(M =Cr.

[MRuCo(~~-S)(CO)x(,~i-CiHj)l

l-S)(CO)x(,li-C.cH,Mr)]

(K = MC. t’h~

(R = Me. H. Cl)

[MCo3(~-CO)~(CO)s(ll’-C.iHi)l (M = MO. W) [CrWPd2(/1:-CO)~(,l-CO),(PPh~)~(,I”-CjHs)2]

[MoRuCo(,l?-,l’-RC?H)(CO)x(,l’CSHi)l

[MoFcCo(/l

[MoCo2(,1?-CR)(C0)8(115-CiHi)]

IMCo2(,r1~CR)(CO)x(,li-CsHs)] (M =Cr. Mo. W. R = H. Me, Ph: M = MO. W. R = Cf,H~Me-I)

MO. W)

(M. M ’ = Mu. W)

IMFeCo(~ri-S)(CO)x(,I’-CiH?)I

(M = Mo. R = ?rlr. Ph.

[MoFeCo(E13-PPh)(CO)x(ri’-CiHi)l IMM’Fc(/l?-S)(C0),(,)‘-C5H;)j

[MoCo2(,li-PPh)(~-AsMe?)(CO)(,oI

IMCo2(,(~-C;eR)(CO)s(,li-CiHF)] Bu’: M = W. R = Bu’)

[MCo2(,li-CR)(CO)x(,~“-CiHj)l (M = Mo. R = CO?menthyl. H: M = W. R = H)

[Mo2C02(,1-CO)?tC0),(,~~-C~H~)~l [Mo,Ni?(lrJ-A~)(/13-As)(CO),(,~~-Cir~~)~,l

[MoC”~(~-C0)3(CO)x(,l’-CjHi)l

IMoNi2(,li-CCO?Pr’)(CO)~(,li-CiH?);I

Ml.,,

[WH(CO)I

(IZ/loCI(CO);(rii-CjHi)l

[CO,(CO)I~I. [MH(CO):(,jk’iHi)] IC~~Pdl(/l:-C0)2t/1-CO),(PPh;)~(,,”-CiHi)II. (qkiH>)] [Rr;Pt(/(-H):(CO),~I-.

tR = Mc).

(R = Me. H. Cl) [MoCI(CO):(,li-CjH,Mr)l

(KuCO~(/I I-,~‘-RC~H)ICO)<,I.

(hloH(CO):(ri’-(.iHi)l IFe2Co(/r-H)(//;-S)((‘0)91.

IMoCI(CO);(,l’~C~H~)]

VI (Corlrimret/)

I(‘oi(lr~-CR)(CO)vl:

TABLE

I)

D

0

I)

D

I)

FIG. 10. S)n~hrws UT ~111\4licl)ne-cnpped CIUIICI~ hq mtal exchange: (i) IMoX(C.C)):(,,i-C.~Hi)l. X = H. Cl: R = Me. (Ii) IM(CO);(r~5-C~Hs)jm. BPK M =Cr. Mo. W: R=H. Me. (iii) [M(A\M~~)(CO);(,I’-CH~)~. M =c’r. MO. W: R=H. IMC. Ph. C~HJM~-I. (iv) IppnllM(CO)l(rii-CiH5)1: R=CI (v) [M(CO)3(~~‘-C~H~)jm Nat. K+: M=Cr. Mo. W: R=CI. (vi) [M’(CO)?(,li-CiHi)]: ICI =Mo: M ’=Mo. W. (iii) [M(CO)I(II~-C;H~)]~: M= MO. W CiH,R’)/-: M = Mu. \V. R’ = C(O)H. C(O)Mc. C02Et. R = Ph. M = Mu. \V. R’ = H. R = H. Mr. Ph. M = MO. R’ = H I<-Sil;tj. II. (Lilii [bl(CO);i,/iR = C02menth~l: M = MO. W. K’ = C’02lzt. K = Me: M = Mo. W: R’ = Mr. R = Ph. CO?Et. (ix) [Fr(C0)~1’~/ Hi: R’ = C(O)H. C(O)Me. COzEt: R = Ph M = Mo, M ’ = Fe: R’ = H. R = CO? menthyl: M = MO. M ’ = Fe. R’ = Me. R = C@Et: M = MO. W. M ’ = Fe. (x1 [M’(CO),J’-/H+: R = II. Me. Ph: M = Mo W: M ’ = Ru. OS: M. M ’ = Mo. W. R = Ph. CO2Et: K’ = Me. (xi) [M(CO)~(qi-L)12: M = W. L = CiHj. K = Me: M = Mo. 1. = C‘H,Pr’. CsHi. CqH7. R = CO: menthyl: M =Mo. L= C+I<. CiH4Me. C5hlr5. R= Pr’. (xi~) [Ni(Co)(,~~-CiHi)l-): M = MO. L= $CyHi: R = Pr’. Mr. (xiii) INi(qi-CiHs)~l: M = Mo L = ,/“-CiHi: R = Pr’.

86

WATERMAN et a/

as the Co(CO)j unit is the most readily displaced group in metal exchange reactions. 16.17.28.30.5~~.110.112.1Ih.117.13-1 Early studies in this area have been reviewed;’ more recently, extensions to the metal exchange procedure have been explored using different /L~-CR groups. and varying coligands on the metal exchange reagents. Forcxample. the reactions between ICo3(~n3-CR)(CO),,I (R = SiEt,. H. Cl. Br) and [M(CO)~(I&H~)\~ (M = MO. W) afforded [ MCol(/l.;-CR)(CO)x(,IS-CjH)]. the reactivity of the /I-CR apical substituent resulting in low yields ofthc products.’ Ii The reactions of [C(~~(/II-CPh)(C0)9] and [ M(CO)7( qi-C5HIR)]- [M = MO, W: R = C(O)H. C(O)Me. COlEt] afforded [MCol(,lj-CR)(CO)H(~li-C5H~R)I; incorporation of an electron-withdrawing group on the cyclopentadienyl ligand reduced the activity of the exchange reagent.“’ “I An alternative route to IMCol(/t I-CR)(CO)~( rli-C5Hi)] (M = Cr. MO. W; R = H. Me, Ph) involving clectron transfer catalysis has been demonstrated.’ “I Reaction of [C~~(E~~-CR)(CO)~I.the metal exchange reagent. and a catalytic amount ol‘sodium diphenylketyl under varying conditions afforded the desired clusters in good yield. This reaction procecdcd rapidly at room temperature, in contrast to the classical metal exchange reaction which required heatin f in benzene for 3 days.‘“.“’ Many examples of sequential metal exchange at face-capped trinuclear clusters have been reported. Two successive metal exchange reactions cm afford tetrahedral clusters which are chiral by virtue 01‘havine(Tfour different core coiistituents (Fig, 40). Metal exchange can proceed by ;I further step: the cluster [MoNil(Cli-CPr’)(CO)~(Ij-CiHj),ISh is an example ol‘metal exchange in which all three CO(CO)J units ofthe prccursorclustcr have been replaced with other moieties. While the apical substituent in these clustera has usually been an alkylidync group. other face cappin g ligands have also been successfully employed. Foi example, the clusters IMFeCo(lr:-X)(CO)x(ll’-C.iH5)I (M = MO. W; X = S. SC. PNEtl),lY 12’) IMoFeCo(/li-S)(CO)x(,15-CiH~R)I [R = C(O)H.C(O)Me.COz Et].“’ I{ MFeCo(br ?-S)(CO)x(,lS-CiH,))l IMoRuC~(E~~-S)(CO)~(I]-C~H~)I,‘~” and (IL-R)] [M = Mo. W; R = ~-CH$Z~,HJCH~. ~-C(O)C~,HJC(O)I”’ were formed by metal exchange reactions with [M’Co2(/1;-X)(CO)UI (M’ = Fe, Ku). itself prepared by metal exchange from the precursor cluster ICO~(~L:-X)(CO)~)] (Fig. 1-l ). The metal exchange products [ MFeCo(El?-S)(CO)x(,I5-C5HJR)I (M = Mo. W: R = CHO, OMc. CO?Me) reacted with nickclocene in rctluxing THF to afford IMFeNi(El:-S)(CO)i(,I’-C~H5)(r7’-CsH~R)J.’” IFe,Co(lr-H)(lli-S)(CO)uJ. prcpared from [ FeCo~(/li-S)(CO)sl. reacted with IM~CI(CO)I(II”-C~HJM~)~ to afford [MoFeCo(~~-S)(CO)x(,15-C5H~Me)] and IM~~F~(/~~-S)(CO)~OI”-C~H~M~)~I.’” Similarly.reaction between [R~CO,(/~~-S)(CO)~~]and Nal[(CO)jM{ I/‘-CTHJC(O)4-Cc,HJC(0)-II’-CjHJ}M(CO)jl (M = Mo, W) has afforded the clusters IMRuCo (/li-S)(CO)x{ ~~s-C~H~C(Oj-4-C~H,C(O)-)15-C~H~}MRuCo(~~i-S)(CO)x] in which the exchange reagent links two cluster cores (Fig. 42).‘“.“’ and [MRuCo(y,S)(CO)&$CiHJR)] IM = Mo, W; R = C(O)H. C(O)Mc, C(O)Ph. 4-C(0)C,HJ

FIG. 41. Sqnthtws ot‘ cluer\ I\ 1~11other face-cappill g Iigrrntl~ bp meral rxchan;e: (I) [W(CO)~(J~~-C~H~)]~. M = Se. PRu’. PPh. PNEt2. PSEt. (iii) [MoCI(C0)3(,1’-CiH,Me)l. X = S. Ci;,) [Fe(C0)~1’-. H-. (VI IM’(AsMe)(CO)i(ll’-CiHj)l. W. M = Ku. X = S: [M’(CO)i(,l’-CiHi)]~. M = I+. M ’ = MO. W. X = S. Se. PNEt2. (\i) IM’(AsMe2)(CO)?(,,‘-CjHj,l. hl’ = MO. W: [M’IA\M~~)(C.O);(,~~C~~~~~~. M ’ = Cr. MO. W. M = Ku. X = S. (viii) IM’I<.~);(,,~-C~H~)]~.M’ = Ma W. (ix) W. K = C(O)H. C(O)Me. (‘O:Et. U&Mc. M = Fr. X = S. (x1 IM”(C0)7(,li-CiH,R’)I~ M ” = Mo. W. R’ = H. C(O)Me. M = MO. w.

Ku. X = PPh. Iii) hl = Fe. X = S M = Fe. X = S. M ’= Cr. MO X = S. (vi?) LM’(CO)dqi-C~Hs)J2 [M’(CO)~(I,‘-C~HJR)] : M = Mo CO?Me. Me, R = CO?Et. C02Me

88

WATERMAN

et a/

s

Ku- \!/

c-0 I

0

CO

,' (‘

+

M

0

l'-

(‘ M

C02Mc] were obtained by metal exchange from the same ruthenium-dicobalt precut-sol and analogous functionalized (cyclopentadienyl)metal carbonyl anions. “x” Related reactions of the selenido-containing cluster IRuCO~(/L 3-Se) (CO)u] with the functionalized (cyclopentadienyl)molybdenum carbonyl anion reagents afforded the analogous [MoRuCo(,l-Se)(CO)x(~~~-C5HIK)I. and with the linked dianionic dimolybdenum reagent afforded [ MoRuCo(/l j-Se)(CO)x( ,j5C~H~C(O)-~-C~H,C(O)-)~‘-C~H~}MOKUC~(/~~~ A capping arsenic atom has been employed; one or two Mo(CO)$ q5-CjH.i) vertices in the trimolybdcnum precursor IMo(~~-As)(CO)(,(,I’-C~H~)~~ were replaced (Fig. 43).“‘.“” The flexibility of this procedure has been further demonstrated utilizing clusters with capping germylidyne groups (Fig. 44).“’ Metal exchange methods have also been utilized with alkyne-bridged clusters. For example. LRuC~~(~~~-)~~-RC~R’)(CO)cI] was the precursor to 1MoRuCo(k~ 3-~~‘RC2R’)(CO)x(~$CjH5)] (R, R’ = Ph, Me), [ MoRuNi(,li-11’-MeC2Me)(CO)i(rliCjH5)2], and (MoRuRh(jl-q’-MeCZMc)(CO)s( q5-CiHg)) (Fig. 35). “’ Although metal exchange procedures to afford “very mixed”-metal clusters have been utilized most frequently with trinuclear clusters, reactions involving tetrunuclear clusters have also been successful. The reaction of [ COJ(/L-CO)JCO)~,] with [MH(CO)~(&$H~)j (M = Mo, W) afforded the tetrahedral cluster [ MCoJlcCO)i(CO)x(q5-C5Hs)].13”A similarreaction between [ CO~(~L-CO)~(CO)(,(II~-I .3,% CbH3Mej)] and IMo(C0)3(,15-CiHi)]l likewise afforded [MCo;(/XO);(CO)x

“Very Mixed”-MetalCarbonyl Clusters

89

, ICO((‘O),(I~‘-C~H~)I

\

(t15-CiHj)], togetherwith [MolCol(~l-C0)3(CO)7(115-CsH5)11 (Fig. 46).‘;‘Thc butterflycluster ICr2PdZ(,I;-C0)7(/L-CO)~(PPh~)~(~~~-C.iH~)~l reacted with [ WH(C0); (qS-CiH~)] to afford [CrWPd2(/1;-C0)7(/1-CO)J(PPhl),(,15-CiHj)~l (Fig. 47).“” The “spiked” triangular cluster [ Re3Pt(y-H);(CO)IJ] reacted with ;1range of metal carbonyl anions ([HRe~(CO)~~j-, (Mn(C0)5]m, [ W(CO)j(r75-C~H5)]p. ICO(CO)J] ) and metal carbonyl hydrides (IReH(CO)a(PPh3)I. [ReH(CO)j(PPh\)z]) to afford

WATERMAN

90

“spiked” triangular cluster products. Metal tnixcd”-metal clusters may also be possible.

et al.

exchang ’ at higher nuclearity but has yet to be exploited.

“very

Reactions ofclusters with tnonortucltm ordinuclear metal complexes frequently provide ;I method of expanding the metal core nuclearity under controlled conditions. The majority been prepared frotn it-and-hope”)

of mediumand high-nuclearity homotnetallic clusters has lower-nuclearity cluster precursors by thertnolyses (‘.heat-

reactions.

This

is less true

of the heteromctallic

clusters

in this

“Very Mixed”-Metal

section.

with

trolled

means

three

synthetic

of obtaining

tion by a tnetal complex complex

(“redox

of flexible

nucleophile

condensation”),

ligands.

high-nuclearity

and

cluster

VII collccls

“very

of pre-existing

cursor

cluster:

Sulfido angular

on a cluster,

or a cluster

nucleophile

on a metal

clusters

stepwise

synthesized (M =Co,

linkage)

the lighter the

cluster

heavier

core,

SBu’)( If-cod)(q5-CiH5)2] Heating

rather

yieldin

usual

transfer

r$cyclopentadienyl

dependent

to afford

substitution

on the prc-

ICO,(/I~,

g the crystallographically with cluster

a spiked

by

characterized

butterfly

expansion.

I~‘:I/~‘-

reacted coordination

Photolysis

of the tri-

or [Cr2Rh(/li-S)1(/1-

of (Fel(p-S)I(CO)&

afforded

the clusters

(M = Co, R = MC; M = Rh. R = H)

the tetrahedral

some metal-metal

the “bow-tie”cluster

or contraction

[Rh~(/AJ0)3(CO)I,]

[Cr$Zo(~3-S)2(~-SBu’)(CO)~(q5-C afforded

alower nuclearitycluster a butterfly coordination

Table

[Cr(C0)3(qh-PhCzPh)]

products

cluster

in the presence

than the expected

tnaintain

and

successful.

by expansion

fragmented

[CrlFe~M(/13-S)1(/1-SBu’)(C0)(,(,7’-C5HIR)21 (Fig. 49).‘57

:I variety

of tnetliutn-

highly

[Cr$Yo(/~~-S)2(/1-SBu’)(C0)2(q5-C~H~Me)2]

diphenylacetylene

employing

assetnbiy

Rh) with

afforded

cluster

tI~:‘16-PhC2Ph)(,l-CO)~(CO)ll,l. (Fi g 48). ‘55 bridging ligands can facilitate clusters

procedures

and stars have all proved

acetylene

PhC2Ph)(CO)&Yr(CO)j], [CrRhJlrs, geometry

a coilsubstitu-

complexes.

whereas

of the

to afford

Nucleophilic

of [MJ(/I-CO)~(CO)~,I

has a pendant

extensively

nuclearity.

systematic

mixed”-metal

(which

etnployed

of different bridge-assisted

Stone’s chains

cluster

The reaction

expansion

procedures clusters

91

Carbonyl Clusters

jHs)2]

cluster

in the presence

JCr$Zo(/~3-S)JCO)(

of

r~~-CjH~)j].

product.‘“’

connectivity

Sulfide bridging lipand< can also upon cluster fragmentation. Reaction of

ICt-~Ni(/l3-S)I(/I-SBu’)~(t~~-C~Hs~~]

and [Co2(CO)t;]

afforded

[Cr2Col(~~-S)(~I-S)7(CO)~(r7’-CSHj)(175-C~H~BLt’)] geometry: this cotnplex reaction also involves

of a tertiary

butyl

group

ligands

(Fig.

50).‘J’

frotn

the IL-SBu’

ligand

to one

with an unof the

OE sti
ttl

cl-1

ftl

C f

3

93

94

P

II r

95

96

“Very Mixed”-Metal

Carbonyl Clusters

97 Ph c (‘0

‘/ CO

. Rh

Expansion electrophiles L = CiH5;“” M=Pt, (Fig.

of the capped has

octahedral the

[ R~~(/Q-C)(CO)~I]‘~

clusters

M = Pd, L = q3- I -phenylallyl;

L=Me?‘“’ 5 I ).

afforded ). with

I .4-bicapped

with

lRe7M(~I~,-C)(C0)2,(L)1’-

platinum

group (M = Pd.

‘Q M = Pt. L = I$ I -methylallyl:‘“’ octahedral

coordination

geometries

98

WATERMAN

A number

of mononuclear

and binuclear

in the formation

and expansion

the coordinatively

unsaturated

(M = Re, Mn) ally

short

(Fig.

afforded

52).“’

The

co)dco)~),,I’-~

forded

Re-Pt (11

utilized.

bond

reaction

[ Re~Pt(C0)1,]‘~.

with

metry,‘5’

whereas

(CO),

with a butterfly

:I7

reaction

[Rc3Pt(/l-H)(,(CO)I(l,

with reaction

or metal

carbonyl

anions

sion

the

of

metal

[RezPt(/l-H)1(CO)x(M’}I W(C0)3(~&C5Hi), cursors

core

the

butterfly

(Fig. S3).”

a bow-tie

core

afforded

[RejPt(/l-H)

displacement affkcling

[(M’) CO(CO)~J

can also be successfully

= Mn(CO)5. (Fig.

SS).7’.73

employed;

it reacted

the structurally (Fig.

Re(CO)4(PPh3), High oxidation

with

with

characterkd

S4).7’ In a related

of the rl’-cod the spiked

reaction

gco-

[Re,Pt(/r-H)1(CO)x(,I.r-cod)]

core geometry

nuclearity.

[(Pt3(/~-

complexes af[ Re(COI,]

(“swallow”)

of [RelPt(ln-H)7(CO)x(r~‘-~~~l)l caused

example

clusters

and [ Re7(/1-H)z(CO)s];

of H2 to al’ford

‘. unusLl-

rhenium

with

[RQ(/L-H)(H)$CO)~J

of [Pt( I~‘-uK!)~\

of

[M(CO)i]

of the rhenium

of I( Ptl(,r-CO)~(CO)I),,J’-

in the presence

ries of reactions,

for

the nnturc

an edge-bridged

Reaction

with

the columnar

I‘rom

on

core geometry

by reaction

[ RQ(/L-H)$CO)~]

fhrmed

with

have been utilized clusters.

[MPtj(/c-dppm)l(CO)il

bein, (7 noted

c IO) are dependent

For example,

was prepared

clusters

distances

clusters

complexes

platinum-rhenium

[ Pti(,lI-CO)(/1-dppm)31’t

the tetrahedral

metal-metal

rhenium

of mixed cluster

et a/

metal

\e-

hydrides

ligand and expantriangular clusters Rc(CO);(PPh;)2. state rhenium pre-

of [ Pt3(~c-CO);(PCy;)-,I

with

“Very Mixed”-Metal

Carbonyl Clusters

1"

Pt

’ [Re,(~-H)2((‘O)xI w

H

100

WATERMAN

ef al

. structurally characterized IRelO,] gave [ RePt~(/l-O)l(/l-OH)(CO)~(PCy-,)~]i with the unusual bi-butterfly cot-e geometry shown in Fig. SO.‘sx The rectangular cluster IP~J(,I-OA~)~(,~-CO)-~I~ ’ has acetate groups which are readily displaced; reaction with ( Mo(CO)-l(~&CgHi)]mm afforded IMoiPd4(,c {CO)I(/I-CO)~(,I’-C~H~)J~‘~ with a tetra-edge-bridged quart: core geometry. and the palladium atoms in the unusual + I /? oxidation state.‘“‘.‘“” whercas reaction with [Mn(CN)(CO)I(~IS-CSH~M~)l-~ gave [Mn~Pd~(~l-NC)I(CO),7(lj5-CgH-I Me)J].“” which consists of two MnlPd? chains linked together by bridging CNtnoietics (Fig. 57). The V-shaped cluster IWPdl(/l~-CO)(/I-CO),(/r-OH)(Ph)~ (PPh3)$ q5-C5Hg)] reacted with [ WH(CO);( &CTH~) 1to afford the butterfly cluster [ W,Pd2(/~3-C0)2(~-CO)J(PPh3)l( ,$CiH5)l].“” The closely related clusters [ MzPdl( /l>-CO)I(/I-CO)J( PRJ)z( I15-C.iH,)21 (M = Cr. MO, W: R = Pr’. Et) wwc

i

“Very Mixed”-Metal

formed

by

nucleophilic

[ MPd,(/13-CO)(/K

displacement

metal

have

been

clusters.

forded

in the introduction seldom

Heating

(I % ) yield.“” suitable

allhrded

by

[ M(CO)j(

On

employed

to this section, to afford

higher

q’-C~H~)l

purely

therrnolytic

nuclearity

“very

[ W21r2(CO)lo(175-C5HS)21

the heptanuclear

(R = H, Me) provide with

of chloride

101 at

I)(I-~-CO)~(PR~)~(II~-C~H~)].~”

As was mentioned cedures

Carbonyl Clusters

cluster

m refluxing [W;lr~(/l-H)(C0),2(17S_CjH5)11

thermolysis. a source

organometallic

the

clusters

promixed”-

tetrahydrofuran in a very

al‘pool

[ M~~(,~~-As)(CO)(,(II~-C~H~R)~~

of MoAa(

$C5H4R)

reagents:

thus.

fragments

reaction

with

which

can combine

[Co(C0)2(q’-CiHj)l

[ MOCO~(/~~-AS)(/~~-CO)~(~~‘-C~H~)~(IJ’-C~H~R)],’~~

whereas

reaction

with[Rh(C0)~(~~5-C~HS)](R=H)~~~vc[MoRh,(/~l-As)(~c;-CO),(CO)(~~i-C~H~)~I (Fig.

58).“5

In

contrast.

photolysis

of

[ Moi(,ll-A~)(CO)(,(,~‘-CjHs);I

in

the

102

WATERMAN

et al.

presence ol‘INi(CO)(lj’-CjHj)]? afforded the metal exchange product IMoNi$/L {As)(CO)~(I&C~H~)~] together with [MolNil(,l~-As)(El;-As)(C0)7(,lj-CsHi)(,1. shown crystalloeraphically to consist of Moj and MoNi2 triangles linked by ;I /c4-As bridge.‘ZX The triangular cluster [Nij(/l;-CO),(rli-C,Hs);] reacted with [ Mo(C0)$q5-CsH5)]2 by core expansion rather than metal exchange. affording the pat-magnetic [ MoNi;(Eci-CO);(,I’-CsH~)~] (Fig. 59): structural characterization 01‘ the analoguc [MONi~(EL;-CO);OJ’-C~HS)3(I,‘-CiHIM~)] (prepared by an alternntive route from dinuclear precursors) contirmed the tctruhedral core geometry.“‘” Rraunstein and co-workers ha\,e demonstrated the utility of carbonylmetalate anions and dppni-stabilized triangular Inixcd-metal clusters as precursors to clustcrs wilh spiked triangular core geometries. with the products retaining the facecapping and bridging ligands of the mixed-metal precursor (Fig. 60).55~142~‘1i The exocyclic metal-metal bonds can be cleaved in some imtances. carbon I~OIIOV clusters by loss of the ligated ide and halide reacting with the -‘spiked” triangular with one ecluivalcnt metal spike. ‘Q Reaction of[ Mo,Pt(CO)(,(NCPh),(IJS-C5Hj)7]. ofdppe proceeded with cluster core expmsion to afford the spiked triangular clustcl IMo2Pt,(CO)(,(dppc)(115-CjHj)ll, with the bidentatc Iigmnd chelating at ;I platinum

“Very Mixed”-Metal

Carbonyl Clusters

103

atom.“’ Similarly, the palladium-containing analogues [M,Pd(CO)(,(NCPh)2(IjSC5H5)2] (M =Cr, MO. W) reacted with phosphines to give the isostructural [ M2Pd2(CO)6(PR3)~(q5-C~H5)~].” In contrast, the platinum-containing chain complexes [ M2Pt(C0)6(NCPh)$ $-C5HJR)z] (M = Mo, W; R = H, Me) reacted with phosphines to afford the butterfly clusters IM2Pt3(~~I-CO)(y-CO)J(L)2(,ISC-;HIR)2] [L = phosphines. PhlPCHIPPh~Mn(CO),(rI’-C5HJMe)].~~..i’ As can be seen in Fig. 40. a significant number of mixed-metal clusters have been derived from the triangular cluster [Co3(~.(I-CR)(CO)~,]. Whereas further treatment with molybdenum, tungsten. or nickel complexes us~lally induces additional metal exchange, treatment of [MoCO,(~“~-CCO~P~‘)(CO)~(,~‘-C~H~)I, [ MoNiz(/iICCO,Pr’)(CO)~(lj’-CgH5)3]. or lMoCo,(lr~-CCOIPr’)(,r-CO)(CO)I(lli-C~H~)~] with [Fe?(p-CO)I(CO)(,] resulted in cluster expansion forming [ MoFcCo~(lr~and CCOzPr’)(CO)I IO~~-C~H~)]. IMoFeNil(/13-CC01Pr1)(CO)j(II-~-CSHS)i], respectively. with butterfly coordinaIMoFeCo2(/li-CC02Pr’)(C0)5(q5-CsH5)j]. tion geometries (Fig. 6 I).‘” Similarly, photolysis of [MRLICo(Il~-)I~-MeC2Me) (C’O)x($CjHj)] (M = Mo) in the presence of [Fe$/KO)JCO)(,] afforded [ MoFeRuCo(/l~-,7’-MeC2Me)(CO),0(115-C5H,i)]. and both the molybdenum and tLln:rsten-containing clusters reacted with [ Rh(CO)$ &YiH5)] to lip-m

104

WATERMAN

et a/

[ MRuCoRh(~13-r71-MeC1Me)(CO),(,~i-C5HS)II sitnilar

fashion.

metal exchange

CM~)(CO)~(I$C~H~)] products

with

(M = MO, W) [Ru(C0)~j’~

(M = Mo. W) afforded

S. PR, CR;

R = MC. Ph, Bu’;

AsMe~)(C0)7(r&C5H5)~l reacted

with

(M.

CO under

slightly

of ;I Co-As

unit

tetranuclear

intertnediates

metal-tnetal

bonds using

formation

and eleven

metal

work

has been

the preparation

elevated

and

preasurcs

with

trinuclear

tetranuclear

clusters

[MM’M”C~(EI-S)(/Icore

products;

(7 to addition

corrcspondin, have reported R = Me,

fragmentation at normal

and

pressure.

of CO and rupture

under

has been

of I MoWzPtz(/l

CO)~(,(-PPh2)2(C0)2(II~-CsHs)il

conditions.

of two

of group

This

briefly

work

here.

h-group

(M’ = MO. has been

Figure

re-

63 reveals

of three. four, five. six. seven. nine. ~I.1S,-lh.I~‘I. 151)IS’,ISh IhI).I(,S atld this

to embrace of the Rug

to include

4)(/1-CC~,H1Me-4)(/1-CO)~(C0)5( examples. with the preparation

only

complexes mild

extended

a source

expanded

expansion [LM’(CO)$XYR)J

Ph. C(,HJMe-4).

bc summarized

of chain

aloms

the systematic

(M = Ni. PO and

and will

the logical

[ Ru(CO)~(I~%‘~H~)],

all combinations)

to afford

I/‘-CiMq:

elsewhere’

methodology

the core-expanded

The

(M = MO, W: M’ = Fe. Ru, Co; E =

nol

[M(q’-cod)?]

L = q5-CsHj.

viewed

In a

are observed.“’

Stone and co-workers IO clusters

62~.‘“~

at [MCO&L;-

M’ = MO. W; M” = Fc, Ru: not all combinations)

elimination

W:

as by-products

[M~Co~(~~~-~~2-M~C~Me)(CO)XoJS‘CjHj)7].”’

[MM’Co2(/n3-E)(~~-AsMe~)(CO)x(t$C5H~))

(Fig.

and [OS(CO)J]‘~

other

metal-tigand

i‘l.agnicnt).J”

merallacarborane

1-,17-7.9-Me2-7.C)-C1B

systems

More

clusler

recently,

compounds

toHx- I2-OC)(/1

(c.g. this with

q-CChH~Mc-

I$C~H~)~] (Fig. &I).“” and tunfst”i-t-hodiutn of [WIRh,(/lj-CMe)(/l-CMc){/(-C(Me)C(0)}(/Ifrom

[W7Rh2(/1-CMe)lIr-C(Me)C(O))(/1-C0)

(~~-PPh~)I(CO)I(~~‘-CjH~)~l.X2-‘0’ Attempts toextcnd the lengths ofchains beyond seven metal atoms resulted in chain cyctization to form macrocyclic “s(ar” clusters in instances where the heptametallic precursor has terminal gr(jLtps (Fig, (~~),‘“‘~‘““-‘“‘~‘“5 but the chains can be successfully heptametaltic intermediate attributed to differing chain

has terminal conformations.

[ Pt(q’-cod)]

groups

tungsten carbyne extended if the (Fig.

63).

;I result

“Very Mixed”-Metal

Carbonyl Clusters

105

1;~;. 63. Formation of chain clu\ter\: (i) [Pt(qkJ)~]; M = Ni. Pt: M’ = Mo. W: R = Mc. Ph. (‘(,H4Mc-4: 1. = ,&C5Hs. q5-CsMq. (ii) [ W(=CR)(CO)2(L)]: M = Ni. Pt: M’ = MO, W: R =Cc,H4Me1. Mc: L = q’-C~H~. ,,‘-C>Mey: not all combination\. (iii) [Pt(q’-cod):l: M = Ni. Pt. M’= Mo. W: K=Mr ld=~li-C~Mc~. (iv) 2-3.S[Pt(,~1-cocl)~J: M=Ni. Pt: M’=Mo. W: R=Cc,11,M+4, Me: l.= q5-C~Hi. I/‘-CiMq. (v) [W(=CR)(CYX2(L)I. 3 atm CIH4: M = Ni. Pt: M’= MO, W: K = C6H4Mc4. Mc: L = rl-C?Hc q5-C5Mc~: not all combination?. (vi) [NI(I~~-c~~)~]: M = Ni. Pt: M’= W: R = Me, 1. = ~,~-CiMei. (cli) [We], 3 atm C~HJ: M = Pt: M’ = W: R = Mc: L = ,/‘-CiHi. rli-C<Mci. (viii) I .S[Pt(1,‘-cotl)21: M = Pt: M’ = MO: R = Cc,H4Me-1, Mc: L = qi-C5Hi. ,J~-C~M~;. (1ri)21W(~Me)(CO)(,1’-CiHi)l: M’= MO. M”= W:L=,~~-C~Hi.(1)~.~IPt(,~~-cod)~1,ji~tlllC~H,.

106

WATERMAN

et al.

RI ” (‘R /\

(a 1

(hi

(a) M = Mo. K = Cc,HJMe-4: M = W. R = Ph. ~bt M = Pt. M’ = Si. XI” = FIG. 05. “St~“clu\ter\: W. R = Cc,H4Me-4. Ph: M = Ni, M’ = PI. M” = W. R =Cc,H,Me-4. PI>: M = NI. M’ = Pt. M” = Mo. R = Cc,H,Me-J.

F. Catalytic Research

Studies into

utilitarian

cluster

potential.

ular interest

as many

and late transition Attempts while ‘oeneral 2 reviews

has been driven

involving

established metals

to model precursors

to be comprehensive

transformations clusters

are discussed

clusters

catalyzed

processes

and petroleum

arc summarized

while

the tabulated below

focuses

and

is of particcouple

mid

reforming).

in Section respectively.

has been summarized

the discussion

interest

1I.F. I .,

and heterogeneous

11.F.2. and II.F.3.,

catalysis

and R~s&‘“‘.‘“~

intrinsic

as homogeneous

in Sections

cluster

in scope,

by both

mixed”-metal

hydrodesulfurization

mixed”-metal

area of mixed-metal by Braunstein

“very

heterogeneously

(e.g.,

catalytic

the use of “very

catalysis

catalysis

Catalysis

results

The

in excellent are intended

on the more

recent

results.

Reactivity studies of organic ligands with mixed-metal clusters have been utilized in an attempt to shed light on the fundamental steps that occur in heterogeneous chemistry

catalysis

(Table

and surface-adsorbate

VIII).

although interactions

the correspondence is often

poor.‘6”

between While

cluster

some ofthesc

studies have been mentioned in Section II.D., it is useful to revisit them in the context of the catalytic process for which they are models. Shapley and cc-workers have examined the solution chemistry of tungsten-iridium clusters in an effort to understand

hydrogenolysis

of butane.

The reaction

of excess diphenylacctylene

with

Ke-1’1

W-11

Mu-Co

Metal\

IR~Pt~(l.r-dppm)i((‘O);]IRePti(~-dpprn)?(CO);]\ullide

IW?lr2(CO),,,(rl’-(.,Hi)~/

+ propylene wttide i- cxce\\ propytcnc

+ PhC=CPh

[Mo2Co~(/l?-S),(SPh)z(,i’-CiH1Et)~] + HZ + CO IWhXCO), ,(&‘iHi)] + PhC=CPh

[Mo?C~~(/~,~S)(/~I-S)~(CO)~(,~~-C~H,M~)~] + KSH (R = Bu’. MqCHCH2CH2. Ph) IM~~CO~(,~,-S)(,~;-S)~(CO),(,,~-C~H~~~~)~~ + his-2.3-dirnethylthiil-ant IMo?COZ(/I,-S)(~~-S)~(CO),O~~-C~H,M~)~I + diphenytthictane (c,is or r~zu~.~) IM~~C~~(/~~-S)(/~:-S)~(CO),(,I’-C~H~M~)~] + SCNBu’ IMo~CO~(~&~)(~L ~-S)~(CO),(,li-CjHIMe)21 + thiophenc\ lMo:Co$/1 ;-S)~I<.~)~(,,~~C~II,E~)~~ + PhSSPh [MoIC~~(I-I;-S),(CO)?O~~-C~H,E~)~~ + PhSH IMo?(‘o?(~d I~S),(CO)~(I,‘-CiH,Et)?l + PhSH + CO

Precurror (‘lu\ter

IM02C01(/1;-S),(SPh)2(~li-C~H,Et)21 IMo2Co~(/l~-S)~(SPh)2(l,‘~CjH,Et)~]. PhSSPh. PhS(C‘O)Ph PhSSPh IWIri(p ;-CPh)(lr-CPh)(/l-rigCPhCPhCPhCPh)(CO)j(,l”CiH,,] [W,~I-~(,I:-CP~)(/~I-~~~-CP~CPI~CP~) (,(-CO)~(CO),(,~‘-C.~H~)II jRrPt~(/l-dpp11l)i(C‘[~)~(S)I- + propcne IRePt;(/~~-S)~(/~-dppm)~(CO):Ii + propcnc

[M~~C”~(,~~-SI~(S)(I~‘-C~H,M~)~~ + <-,\-I.% diphcnylpropene [Mo~CO~(/QS)(/I ;-S)2(CO);(CNR)(,I-C~H,M~)~]. [M~~(.o~(/~~-S),(CNB~‘)((.O)(,~~-C~H~M~),~ Saturated and unsauiratrd C,-C, hydl-ocarhow

Product(\)

Tran,formatwn

Modeled

IO6

105. I06 105. I06

7x

62

63.64

63.64

63.64

63.64

68. 103

6X. 103

I03

68. to1

6X. 103. 104

Rd.

108

WATERMAN

et al.

+RSH. -RII

[ Wlr$CO),

I(I]-C~H~)]

afforded

two products.

one of which,

CPh)(/l-rl’-CPhCPhCPhCPh)(CO)i(&CTH5)], the tungsten C=C

scission

via C-C

cluster

to give two

resulting

formations

products,

Curtis

C-C

and co-workers

CsH4Et)2]

have

to understand

lead to C-S

scission

tion reactions

with

processes

studied

alumiiia-supported

desulfuriation

carbons, ligand

cluster

details

investigated.“” Reaction of thiophenol electron-deficient,

were desulfurized

of the thiol with

paramagnetic

which.

in the presence

forded

PhSSPh. cycle

C-C

cleavage:

of organosull‘ur

process.

compounds ;-S)J(CO):(IJ’-

The reaction

catalysts.

pathways

The bimetallic thiols

to RNC.

which

cluster

to parent

hydro-

(Fig.

and unsaturated

clusters

that

hydrodesulfltri/a-

CI-&

replaced

a carbony

of CO,

The combination (Fig.

reactions

IMo~C~~(I~~-S)J(CO)?( regenerated

[ Mo,Co?(

I

( Mo~CO~(I~,-S)(/I~-S)I(CO);

desull‘urization

cluster

66):

hydro-

and (M~~C~~(~~~-S)J(CNR)(CO)(II-C~HIM~)~I.””.’”~

tic and mechanistic

catalytic

suggest

trans-

hydrogenolqsis.“’

dcsulfurizcd

isocyanidc-coordinated

(CNR)(qS-C5HJMe)l]

These

hydrogenolyais

to the commercial

were saturated

The

in butane

[ Mo,COI(EIi-S),(C0)2(,15-CgHJMe)lI

products

and isothiocyanates affording

27).“’

with diphenylaccty-

XXI [ Mo$I02(/1

“MoCoS”

[Mo?COI(II~-S)(,IJ-S)7(CO)I(IJ5-CjH~Me)21 and the cubane

(see Fig.

formation.‘”

studies

in ethane

the rcaction

the desult’urizution

carbons

involved

r/‘-CiH~Me)~]

have been compared

thiophene

bond

cithel

or dimerizution

and phenylmethylidyne

has allylic

and C-C

intermediate

)(/lj-S)$CO)q(

moieties system

as experimental

catalysts,

dehydrogenated

[ M~$ZOI(/IJ-S

one of which scission

core with

have undergone

has also been reacted

to illustrate

over the cluster-derived

alkylidyne

[ WIr$/l?-CPh)(l1(buttcrtly)

ligands

an iridacyclopentadienyl

from

are believed

of an adsorbed with

the alkync

[ W,Ir~(CO)lo(115-CsH~)~]

and yielded

fragments

position;

to give jr!- and Ir;-coordinated

coupling

related lent

atom at the “hinge”

has an open

Kinehave

~~i-C~H4Et)~l jr?-S)JSPh)$

the original

of these two reactions

carbonyl constitutes

also been f’ormcd

the

&C5H4Et)2J. cluster

and af-

the basis of a

67).““.“’

Supported bimetallic Re-Pt catalysts are important in selective reforming of petroleum. It is believed that sulfiding the catalyst before use: gives RcS units which act as inert diluents to reduce the size of :I local ensemble of platinum atoms. Selectivity for desirable dchydrocycli/,ation and isomerizntion reactions

“Very Mixed”-Metal

PllS ‘\

is thereby

increased,

jacent

platinum

Rc-Pt

clusters

with

sulfide,

;I cluster

with

lene sulfide

under

mild

conditions

was then desulfurized

dation

ot’ the 0x0 clusters

dppm)j(C0)3]+

RePt, with

faces,

in metal-metal

propene

sulfide

has recently

and the sulfur

coordinated

in the cluster

complexes

bonding

Homogeneous

atom

catalysis

by transition

with

sulfur sulfi-

;-O),(/L-

an equivalent

in a PJ-fashion

“” Examples

gave propy-

two face-capping “)s”06 * si*lilar and [RePti(/r

(Fig.

clus-

sulfide

a second

been studied;

in

‘~ (n = I

of propylene

molecule.

metal clusters

of the speci tic transformations.

to the tetrahedral

and propenc:

[RePti(LLi-O)(p-dppm)$CO)jl’

propylene

was generated

were added

ad-

On reaction

[ RePti(/l-dppm)z(S),,(CO,i]

to give a cluster

and another

several of rhenium

hypotheses.

of one equivalent sulfur

requires

sulfidation

for these

atoms

to give

a rhenium-coordinated

bridging

perspective

as evidence

one or two sulfur

atoms

propene

studied

which

Metalloselective

[RePti(/l-dppm)3(CO)J+,

or 2). Reaction

of alkanes,

is diminished.

has been

109

c

and hydrogenolysis

atoms,

propylene

ter cation

Carbonyl Clusters

with

of

a decrease

6X).‘“”

has been reviewed of very mixed-metal

from

the clus-

ters catalyzing processes homogeneously are collected in Table IX. As is generally the case with homogeneous catalysis, the catalytic precursor is well defined. but the nature of the active catalyst is unclear. Sulfided cial

bimetallic

clusters

hydrodesulfurization

geneous

catalytic

behavior

which

(HDS) studied.

mimic

catalysts Reaction

the metal have

been

composition prepared

of thiophenol

with

of commer-

and their

homo-

[ Mo$~,(/L~-S)

111

112

WATERMAN

(P~-S),(CO)J( ~‘-CSHJM~)~] forded only a stoichiometric cally.

The

(Fig.

l4).5x

reacted

cluster

under catalytic conditions amount of HDS products:

regeneration

Under

( I61 %), The residual

to yield

The

octanuclear

laliphatic

(PhCH,OH,

PhlCHOH)

bond and proton

69). The same cluster

Heterogeneous with bimetallic

COS

was recrystallized

was

and PhS(CO)Ph to give

NaZIMo?PdJ(/L3-CO)I(,I-CO)~(~~~-C~Hs)~l

of aliphatic

(MeOH. alcohols.

[MojZo?

catalysis catalysts

transfer

was inefficient

a

EtOH,

Pr”OH.

Dehydration

was

Bu’CH20H)

proceeded

I’ound

and ary-

slowly

under

solutions containing the catalyst under an was not required. Alcohols having no hy-

drogen atom in the u-position were unable available suggest that the reaction proceeded (Fig.

by CO to give

(I7 I c/. based on cluster)

product

mild conditions (60-80 C) in alcohol argon atmosphere: an acidic medium

across the Mo-Pd

dcsulfidation

(S7%‘)?“’

cluster

dehydration

( 1000 psi CO. I SO C) afPhSSPh is formed catalyti-

[MolCo,(l13-S)J(CO)z(11S-CjH1Et)21

PhSSPh

organometallic

(~@)I(SPh)2(,j5-CsHJEt)~] to catalyze

step involved

the same conditions,

with thiophenol

et al.

to undergo elimination. via oxidative addition to give an intermediate in the hydrogenolysis

by metals has been of long-standing metal particular focus. “)‘) Transition

All the data of the alcohol carbene

specie\

of alcohols.‘“”

intercst,‘x7m’“u carbonyls have

“Very Mixed”-Metal

113

Carbonyl Clusters

HI0 (I<(‘1 I I,,

attracted being

attention

Examples Table

as precursors

examined

as precursors

of heterogeneous

catalysis

with

catalysts,‘“’ particles

heterometallic

of controlled

by cluster-derived

cluster\

stoichiometry.

species

are collected

in

X.

A MgO-supported (t/5-CiHj)lj

(Fig.

by IR, EXAFS, hydrogenation

W-Pt 70),

TEM at 1

precursors.

catalyst,

Hz stream of HZ. CO, than

than for

a

from at 400

an

and

order

catalyst

1WIPt(CO)(,(NCPh)2 C, and characterized

OZ. Activity

in toluene

of magnitude prepared

hm

less

fm

the two

I Sh

catalyst

[ Mo7Rh(,L-CO)(CO)d(,75-CjH)31 at room

a

and 60 C was more

monometallic

cwcuation

has been prepared

under

and chcmisorption atrn

cluster-derived

silica-supported

catalyst

reduced

the bimetallic A

to active to bimetallic

temperature.

was

(Fig.

prepared 70)

Decomposition

ti-om

by

anaerobic

impregnation

CH$Zl~

solution,

processes

were

followed observed

01 by at the

“Very Mixed”-Metal beginning

of the CO hydrogenation

decomposition

was complete

ity (ca. 50%’ conversion) higher clude

selectivity

W)

The

were

activated

clusters

in activity

of active

oxygen-containing

under

and subjected

clopcntadienyl

Product

ligands

70)

near

I80 to 300

and its activity

cluster-derived

catalyst

while

activity

cracking

The

compared

and activities

tetrahedral

showed

a

rable

evolution metal

[lr4(CO)1~]

profiles

observed were

the hydrogenolysis activity

(S-10

production

of /l-butane

times)

(7675%) greater

to [It-i + 2Mo2 1. Metal-metal

A catalyst and

were

activation from

All

sample.

on y-A1203

A catalyst

IPtMel(ll%od)]

and treated

catalyst.

identical:

the

presultiding.

for both.

with compa-

catalysts

prepared

from

under

equivalent

exhibited

absorption from

mixture conditions

ot

active

foi

enhanced

toward

ethane

the [Mo21rZ]

(ca. 50%)

spectroscopy

a

were

catalyst

but activity

com-

materials

were

in the activated

was prepared

photoelectron

and

mixtures

In contrast.

interactions

and

on alumina,

in HJ. Materials

spectra.““’ [Re2Pt(CO)I,] (XPS),

chemisorbed cluster was treated with Hz at about I50 C resulting and formation of rhenium subcarbonyls; at 400’ C the sample decarbonylated.

of CO?,

Catalco

nearly

but selectivity

for Cl and C3 production

by IR. X-ray

amounts

stoichiometric

the Molr

the use of Mo K edge X-ray

supported

characterized

during prepared

the same

parable

with

catalysts

at 2 IS C; the [R/loll-~] catalyst

showed

characterized

selectivity

small

of cy-

[ Molr;(l.c-CO)~(CO)x(,l’-C~Hs)]

over the 111-A+ 3Mo2] was

(TPD)

used in the hydrodesulfuriza-

was

70) have been deposited

[Mo2(CO)(,()I-CsHi),].

TiO?.

by evolution

increase

clusters (Fig.

of ;-

SiO2.

in activity upon I 9x in the reduced form.

was enhanced

compositions and

greater

heteromctallic

[ Mo,Ir2(,L-CO)?(C0)7075-CZHi)ll methane

AllO.;,

with the commercial

of both

the for-

decomposilion with

a

[ Mo+ZO$IIJ-S)(/I

oxides

C, together

as

catalyst.

the proportion

100 C. followed

catalyst

6 metal

prevented

increasing

CO

A signiti-

rhodium

precursors

on the refractory

commenced

from

by FTIR.

of a group

supported

pre-

(M = MO,

and EPR.

them to temperature-programmed

ofC0

distributions

as catalyst ct trl. have

CHJ. and Me2.S. The alumina-supported tion of thiophene.

the presence

catalysts

catalyst

characterized (TPR).

for CH4 production, Curtis

(Fig.

Hz. Evolution

with

clusters

products.‘“’

S)~(CO)J(Il’-CjH~Me)2] and MgO,

and cluster

for a monometallic-derived

sites responsible

monoxide

rhodium

[M2Rh(/l-CO)(CO)~(,I’-C5H5)1]

observed

was

The use of these heterometallic mation

monometallic

reduction

to that observed

K the activ-

of carbon

silica-supported

both

At 523 smaller

prepared samples. but has been extended to in-

Hydrogenation

at 37.1 K in Hz and the catalyst

relative

slightly

conventionally “)j This

temperature-programmed

cant increase promoter,

employing

reactor.

exhibited

products.

g homologue.

silica-adsorbed

chemisorption.

in the flow

and tungsten-promoted

has also been compared cursors.

with

oxygenated

the tungsten-containin

on both molybdenum-

at 1 MPa

and the catalyst

compared

toward

115

Carbonyl Clusters

(Fig.

in fragmentation was completely

of [ Re3(Ll-H)3(CO)II] showed

70)

and TPR. The

the rhenium

and to

116

WATERMAN

be present

in a high valent

platinum

is believed

the rhenium

in the sample

Dehydration catalyst

cationic

form

to facilitate

prepared

derived

from

from

has also been examined.

posed under

llowing

Hz at 400

acterized

(Re,Pt(CO),zI

initial

1Pt(NH,)?

to be more

revealed

the cluster-derived

the others:

its resistance

to deactivation

stabilizing

the dispersion

of the platinum.

Each

metallic

transmission showed maintain from

and platinum

MO-Pd

supported

palladium, electron

microscopy,

that the presence the palladium

in

the monometallic

and by weaker

a

TPD

highly

dispersed

than

from the bimetallic

by chemisorption of adsorbed

temperatures

CO. and EXAFS.

The data

precursor

highly

form.

the sample

prepared

palladium

particles

was

In

contrast.

characterized

to

of Hz, CO. and 0,.

in the bimetallic

dispersed

in

70) and monometallic

of molybdenum

precursors

MO-Pd

pre-

Characteriration

H 2 at various

in

I‘rom

to the role of rhenium

(Fig.

was treated

were charmade

than catalyst\

have been prepared

and characterized

to each other

The catalyst

to be more

was attributed 204

+

was deconand

\alt precursors.

catalyst

catalysts

sample

cluster

to deactivation

[Mo7Pd2(En;-CO)1(El-CO)J(PPh3)1(,7i-CiH~)?l

precursors. form

rhenium

The

I Pt( NH?)?]( NO;)?

wore similar

) u toluenc.

resistant

by EXAFS

model

and

ol‘methylcyclohcxane

(>90%

from

MgO-supported

to be near

of a [ Re?Pt(CO),?l-derived

](N03)1

C for 4 h. The catalysts

pared conventionally

cluster

form.

and is likely

The alumina-supported

conversion

was found

in ;L metallic

[RelPt(CO)12].“‘3

for the dchydrogenation

by high

of rhenium

in the prcscnce

NHJRcOJ]

in their selectivities

and the platinum

the reduction

of tnethylcyclohexane

and catalysts

et a/

by larger

helped

to

interactions.~“’

III PHYSICAL A. General

Comments

The focus of research and structure. been largely

MEASUREMENTS

on “very

and the limited restricted

mixed”-metal

physical

to fluxionality

clusters

measurements

has been on their synthesis

ot’these

and electrochemical

clusters

ofligand fluxionality are summarized in Section 1II.A. and reports ical investigations are reviewed in Section 1II.B. The few reports behavior

of these clusters

are summarized

are discussed

in Section

in Section

have thus far

investigations.

Studies

ofelectrochemof the magnetic

1II.C. I ., and theoretical

studies

III.C.2.

B. Fluxionality Ligand the majority

Huxionality of reports

on metal

clusters

focusing

on carbonyl

has been

the subject

migration

of many

on homometallic

studies, tri- and

“Very Mixed”-Metal

Carbonyl Clusters

117

tetranuclear clusters.‘.“‘5 ‘I’ Extending fluxionality studies to mixed-metal clusters affords a significant advantage; mechanistic details may be more accessible due to the decreased symmetry and effective labeling provided by introduction of the heterometal. Additionally. though. activation energies for ligand scratnbling in mixed-metal clusters may diIt‘er markedly frotn those of their homotnetallic ~malogucs, and it would be expected that this difference will be accentuated utilizing “very mixed”-metal clusters. A combination of decreased symmetry. labeled core nuclei. and differing encrgetics for processes involving tnetals with disparate electi.oneFativities may permit discrimination of fluxional pathways not possible in hotnometallic clusters. Despite these significant advantages, comparatively few reports of fluxionality at “very mixed”-metal clusters have appeared. Three major classes of fiuxional behavior are commonly observed in clusters: (A) Metal localic;ed scratnbling. ~tsually seen in M(C0); or M(CO)?L groups. (B) Intermetallic ligand migrations. visually involving CO or hydrides (although examples with phosphines and alkynes are extant) and proceeding via edge-bridged or face-capped intcrmediate5. (C) Metal fratnework rearrangements. Exatnples of all three classes of Huxional behavior have been observed at “very mixed”-metal clusters. It should be emphasized that absolute atomic motions are not accessible: considering ligands rotatin, (7 around a fixed metal core or a metal core rotating within a tixed ligand polytope are equally valid viewpoints (the latter has been docutnentcd in the solid state: see, for example, Ref. 205 ). The former description has been utilized f:u- more often in literature reports and. following this convention, this review summarizes specific cases in terms of lisands exchanging by rotating around a metal core where possible. Table XI sutnmarizes reports of ligand fluxionality at “very mixed”-metal clusters. A number of studies (e.g., Refs. 28, 8 I. I 16, 2 13. 2 14) have reported that both metal-localized and global carbonyl Huxionality occur but give little mechanistic detail. The following discussion focuses on the examples for which detailed studies have been undertaken and/or those for which mechanistic speculation is available. A number of exatnples of metal-localized ligand scrambling have been documented. Rotation of the Ru(C0)~(&gH5) units about the Zr-Ru bonds in the V-shaped IZrRu2(CO)l(r15-CjHj)~] resulted in equivalence ofthe cat-bony1 ligands (Fig. 7 1 ):‘I3 replacing the cyclopentadienyl ligands by CH$CH2NSiMej)z reduced significantly the barrier to rotation in the ruthenium-containing analogue and its iron-containing homologue.“’ A similar rotation ofthe W(CO),( 1$C5MeS) group in [WCO~(~~-CC~HJM~-~)(CO)~(I$C~M~~)] has also been noted.“” A detailed study of the rotation of the M(C0)2(t$-C5RdR’) vertices (M = Mo. W: R. R’ = H. Me) in [MCo:(~3-CC02Pri)(CO)(,(L)($-C5R3R’)] (L = 2C0, Ph2PCHICH2PPhl. Ph7AsCH7CH2PPh,) I’.’ ” revealed that the barriers to rotation of the group 6 tnetalcontaining vertices in these clusters (3742 kJ tnol-‘) are similar to those of the

118

119

120

WATERMAN

Tripodal

(,13-CC02Pr’)(CO),(L)( NMR

studies.

in

vertices

M(C0)2(~5-CjH5.,,Me,,) (,7’-CjH5~,,Mcn)?l.”

Co(C0);

&RqR’)]

A similarly

rapid

et a/

tetrahedral rotation

that turnstile

it could motion

Two

was retarded

localized

was observed

H)2(CO)x(PPhj)2]; bony1

ligands

sponded

to a trigonal

Ph).“”

followed

rotation ofthe

ogous

tripodal

process unit,

Re(C0);

is facile at

procea

phosphine groups

as

car-

correwell

as

has been docu-

e.g. (OS~(/~-H)(/~I-CR)(CO)~~~~

(R =

at room

in the bicapped octahedral IRe,Pt(/1(,Upon cooling a sample of the temperature.‘“’ at the base of the PtMe:

at the three rheniums

rotation:

IRelPt(/l-

of the three

energy

but involving

at the

rotation

the three rhcniums

isostructural

the higher

atom

rotation

at the triangular

of this type at M(CO)4 clusters.

in solution

at one cobalt

a scrambling

wab

while

at the same metal,

in homometallic

by cessation

gation

observed

energy

exchange

Tripodal

C)(Me)3(C0)31]‘m cluster,

twist

Three-fold

previously

H, OMc,

groups.

were

in the Re(C0)3(PPh;)

carbonyls.“x mented

ethyl

processes

the lower

in [ MoCo?

out

but Co(CO)j 71

by ad.jaccnt

exchange

rapid

not bc frozen

in ( WCol(p-EtC,Et)(,l-qJ-CEtCEtCEtCEt)(CO)x], other cobalt

[ M~(E~I-II’-RC~R)(CO)~

was sufficiently

cap

was

at the base of the Rc(C0)3

[Re7Pt(~r~,-C)(C0)~~(r~‘-2-methylullyl)I’decoalescencc

of resonances

froren

lirst.

cap. Investirevcaledanal-

was observed

in the reverse

order to that in the PtMe+ontaining cluster, but it was not clear ii’ this results from a reversal 01‘relative activation cnergics or from chemical shift order. Tetrapodal rotation

of the [Re(C0)3(L)]

[L = P(OMc)3,

P(OPh),J;

barrier to rotation, Several examples

a

vertex

was observed

in [ RePti(El-dl)pni);(CO).i(L,)J-

the trimethylphosphite-containing

result ascribed of intcrmetallic

cluster

had a lower

to steric considerations.‘l’ hydride migration in rhenium-platinum

clus-

ters have been investigated. Hydride hopping between the two Re-Pt edges in trian? occurred at a lower energy than gular IRcIPt(,l-H)2(CO)8(L)] [I, = rl’-cod. (PPh i )_I A similar hydride migration between the two rotation of’ the Pt(H)(L) moiety.“’ Re-Pt edges was observed in the spiked-triangular IRelPt(EI-H)3(CO)lj1”J and

“Very Mixed”-Metal

Carbonyl Clusters

121

[ Re3Pt(/~-H)3(C0,Me)(CO)ti]~,7’ and the “scorpion” [ R~~P~(,-I-H)~(CO)~X~~;‘~an intermediate in which both exchanging hydrides arc bridging Re-Pt linkages in the triangular fragment of the cluster was proposed (Fig. 72). Similarly, the hydrides bridging the Re-PI bonds in the “bowtie” cluster [RelPt(p-H)5(CO)th]m exchange rapidly, with only one ‘H NMR signal ti)r these hydrides observed down to I93 K.7’ Alkyne migration at [MoFcNi(ll3-,l’-PhC1CO~Pt-‘)(CO)(,(rl’-C~H~)~l has been examined;“” a formal rotation of the alkyne rclativc to the metal triangle proceeding by a “modified windscreen wiper” mechanism was proposed (Fig. 73). Carbonyl exchange between tnetals has been the most frequently studied intertnerallic ligand migration in homotnetallic clusters, ~LIL the few exatnplex which have been exatnined in the “very mixed”-metal domain have afforded inconcluhive results. At the triangular cluster [MoCOL(/I~-CCOIPI.‘)(II-P~?E(:H~CH~PP~,) (CO)(,(l15-CsMe5)J, the mechanism interconverting molybdenum- andcobalt-bound carbonyls was not conclusively established. but rnlation of the [Mo(C0)2(11~-

122

W A T E R M A N et a/

Platinum-hound on warming turc ol‘two

isomers

[ Re(CO)j(PPh wrved

phoaphine

;I solution

and I-hcnium-ligatt~l

is formed

which

;)I unit (see abow).

earlier

was proposed,

involving

Pt; face. Thiolate [ Mo,Co$/r

cluster

the intermcrliacy

migration

between

the Co-(‘0

axis and a barrier

2-PBu’)(/l~CO)(CO)(,(

I~‘-C~H~)~]

X0 C. it undcrgocs

an i~mversihle

his-phosphido Few

procc~

in the butterfly

ligand

examples methods

\pannin, (7 MO-CO

of metal at ?er),

Il-amoworh

the MO-CO

bonds:

one’ ligated (Fig.

74).

timcwde

hwc

4 study

cobalt The

with

respect

triangular

through

M and the midpoint

isolobal

analogue

the harrier I .3 hJ nwl

of a d”-ML5

to rotation

to the other

clusters

MO. W: M ’ = (‘(I. Rh) underwent

ligantl

of‘ the M ’-Rh alhcnc

vector

con~plcx.

been that rather.

a molecular

ofthe

M(CO)j

obscr\~ed

the

observed

by clu\-

the Ruxionala twisting mirror

01‘

plane

(M = Cr. unit about an axis

(Fig. 75).““”

The cluster

ij an

In thi\ context.

it is intcrcsting

that

in IMo(‘oRh(,r-C’O)1(C(>)i(,ii-C,Mc,)21

’) is in the rang

with

of the V-shaped

rotation:

intruduwcl

rotation

’.““)

hcatecl at 75-

IMM’Kh(,l-CO)1(CO)~(lii-C~Mci)2J ;I l’ornd

the thi-

:-q’-PBu’Cc,H.,-

when

~e\ealed

was not alhyne

anion

wctors.2’7

tcr IWCol(,(~EtC2Et)(,1-)I”-CEtCEtCEtCEt)(C‘O),1 ity on the NMR

cluster

to at’i’ortl an isomer

and C’o-Co clustcrx.

the

OCCLII’\ with

mrra~qelncnts

mixed”-lnctal

1’

bridging

01‘42 * 3 kJ mol

in [ Mo2Col(/r

tr~unsi’~)rmation

to that

P(OMe):)

ligancl triply

to this motion ligand

britlgcs

has heen ohsimilar

;-C0)(/~Ippm)~(

bonds

The o-phcnylencbis(/r-/o.t-butylphosphido)

NMR

migration

;-S)~(,~-S)(,~-SC~,H_IM~-~)(CO),(,I.~-(‘~H~M~)~I~

elate crossing

twist at ;I

phosphite

ol‘a phosphitc

CO-MO

;I niix-

trigonal

” a Huxional (Pt;(/r

exchange:

27.1 K:“7.1’X

by ;I Irc\trictcd

Intcrmctallic

in the hon~on~etallic

irreversibly

ahow

intcrcomcrt

at [RePt;(/r-dl’p~ii)l(O)~(P(OMe))I~’:

observed

carbonyl

of‘ [Ke,Pt(~l-H)l(CO)s(PPIi~)~I

for hinclerotl

rotation

(AGIS

= 52.3 +

at &ML5

organic

“Very Mixed”-Metal

123

Carbonyl Clusters

\

alkene complexes (AC$=35-80 kJ molK’). A similar rotation, about an axis through the tungsten and midpoint ofthe /I-C-Pt vector, was proposed to explain the equivalence of the radial carbonyls in [W~Re2Pt(@X~,H4Me-3)2(CO)181.X4 The clusters [MF~C~~(/~~-E)(E~-ASM~~)(CO)~(~~’-C~H~)~ (M = Mo, W; E = S. PMe) exist as isomers corresponding to differing positions of the iron and cobalt atoms; detailed equilibration and isomerization studies showed that isomer interconversion does not occur under rigorously clean conditions. but instead requires the presence of impurities, suggesting that radical type metal-metal bond cleavages initiated the isomerization process.‘” Examples of intermolecular ligated metal exchange are also extant. The Vshaped clusters IMPd2(,-~-CI)(CO)~(L)2(175-C5HS)1 (M = Cr. MO, W; L = dmba. dmat) underwent exchange by dissociation and reassociation of the carbonymetallate anion [M(CO)$&~HS)](Fig. 76).2’5 The spiked triangular cluster IR~-~P~(/~-H)~(CO)IJ] exchanged the “spike” fragment [ReH(CO)s] in solution (Fig. 77), in a process which is a formal substitution at a square planar platinum.“’ Such reactions are usually associative; accordingly. a strong dependence on the concentration of added [ReH(CO)S] was noted. “Very mixed”-metal clusters offer significant advantages in Huxionality studies. but these advantages remain to be fully exploited. Studies of tetrahedral rhodium and mixed rhodium-iridium clusters have revealed intermetallic carbonyl ligand site exchange proceeding by way of merry-go-round and change-of-basal-face processes.z06 Substitution of Rh by Ir in the apical site slowed down the former

124

WATERMAN

process.

rationalized

of electron tripodal

rotation

accelerated

process.

electron

density

ofthese

examples

tive energies

involved

of activation.

mixed”-metal

and mixed

metal.

as the

Sd orbit&

an electronic

Replacing

clusters

should

One problem

the apical

from a remote

the vertices

in homometallic

accentuate

these effects,

for fluxional

processes

equivalence

of’ligated

metal

fragments

coordination

number

metal,

and possibly

isostructural

Ir(CO)j [ WIrJCO),

sten, with a sterically processes pies above),

remote

a (formally)

demanding

from

this problem

UC

in proceeding

I( q5-C~H5)]

cyclopentadienyl

the heterometal

(such

ligandl. as with

plane

bonds.

Both

metal affecting

h-CO

rela-

clusters

to alt‘otd

but this remains

involves

by W(C0)$q5-C~H5) introduces

underwcnt

Rh removing

imolving

is that isolobal (e.g.. replacing

clusters

electronegative

between effect

a shift

CO-containing

of Ir by Rh in the basal

more

mally)

higher

Rh inducing

(7 the bridging

rhodillm-iridiLlm

Substitution

rationalized

from the apical

be demonstrated.

face and stabilkin,

iridium

at the apical

this

from the more electronegative

to the basal

state. Tetrahedral

~IX~III~

“very

as resulting

density

et a/.

introducing

increased from

steric

However.

to tung-

for fluxional

the rhodium-iridium

Ii<.

a (f’oreffects

[ Ir~(CO)ll]

eight coordinate

may not bc important.

to

the heteromctal

cxan-

“Very Mixed”-Metal

125

Carbonyl Clusters

C. Electrochemistry The

electrochemical

clsewhcre.“’ as “electron pablc

sinks:”

of multiple

maximized

subjected

with

cyclic

mixed”-metal

to detailed

range of systematically of [ Coj(/13-E)(CO)L,] clusters

capping

group

important an

CMe.

(M = Mo.

may either

reaction

between

by electrolysis

PTol.

GeMc.

Two reduction

processes

ically

irreversible

carhonyl

process,

step: both moving

tion decreased

from a terminal in the order

followed

These

clusters

or provide

Jensen

Cr > Mo=W.

arc chemically

capped 1 (M = Cr. tag-

S. Se) where structural

the

rigidity

(‘I I//. ’“’ have described

(CrCol.

MoCo2.

route

of 3 M-Co

to bridge

(Fig.

WCoz).

with

78).

The

can

be initintcd

I-CR)(CO)~(

direct

I~~-C~H~)) and chem-

and chemically accompanied

on apical

und under

reactive

with the IMoCo2(1(;-CR)(CO)s(,15-CsHS)I

by a

The peak ceparasubstitucnt.

of the elcctrogenerated

temperatures more

bond

theac metals.

with a dependence

out at several

counterparts.

active

by ~111electrochemically

\vith experiments mospheres.

CPh, PMe.

for the [MCo$/l

in the characterization

tricobnlt

especially

The first, an clectrochemically

cleavage position

a

1I.E. I .).

[Co3(/~;-CPh)(CO)~,,I”‘-‘.

EPR data has been used carried

in generating

and K[Mo(C0)~(17-CsH5)]

were observed was

deal

and [ MM’Co(,r;-E)(CO)s(

activated

for the couple

steps involved

of reports

&C5Hi)

CBu’.

examples

(M = Cr. Mo. W; R = Me. Ph) clusters. reversible

GcPh)

thermully

[CO~(/~I-CP~)(CO)~,,I at the potential

ha\.c

(Section

intensively.

state changes.

alkylidync

the cLssical

clusters

[ MC~$/L:-E)(CO)~(

be electrochemically oxidation

of some

than

be

clusters

of electrochemical

procedures

mixed”-metal

formulas

CPh.

in subsequent yields

“very

W; M’ = Fe. Ru; E =CMe.

electrosyntheais

higher

of metal exchange

have been studied

of general

W: E = CH.

;I summary

should

clusters.

varied

triangular

provides

which

mixed”-metal

to act

may be C;I-

of heterometals

the majority

contains

reviewed

potential

atoms

effects

Few “very studies:

their

metal

response.

XII

the success

derivatives Mo.

Table

has been

from

of several

electrochemical

mixed”-metal

given

clusters stems

The incorporation

clusters.

only.

of&&very

Not surprisingly,

CTH~)]

an aggregate

the electrochemical

voltammctry

investigations

clusters

state changes.

to tune

in “very

been

of heterometallic

in examining

in principle,

redox

the opportunity

wide

behavior

The interest

urgon

than their

species. and CO at-

homonucleal

clusters

the most

“Very Mixed”-Metal

chemically

I-eve,-sible.““.“”

The d.c. polarognums

the ~-elated gcrmaniLlm-capped also showed

of’the

supported

by EPR data; the second

(Fig.

X-ray

dif‘fraction

structure

bond.

L~o\~-ternpcratur~ ligmnd

occurred

protonation,

through

and

radical

anion

duction

more

difficult

precursor.

than

clcctron,

While higher

WFe)

to its sulfur trimetallic

capped

clu\tcr

wma.

three (-

an irrevcrsiblc

to arise

of. the neutral showed

radical

reduction.

clusters

[Cr$Jo(/r

have

also been

I~roiii a fasl

two-electron

+O.L? process

(R =

;-Se)(CO)s(

of an electron

Addition nletals

and

intensively

Cyclic

(+0.X()

revealed

one-electron

V). Another

mm

studied.

readcluxtct

clusters

of

01‘ the tetm l’our oxidation

transfer

tetra-cupped

=

;I one-

cnplmf

voltnmmetry

in DMF

V) reversible

(M,M,

proceeded

i-

ncgativc

untlctwent

IOr the \eleniunl

the moat

investigated.

I’C-

[ WFcCo(/~

at more

q5-CiHS)]

tol-

made iron-dicobalt

clustera reduced

at IOU

rmction

heteromctal

[M,M~CO(/~~-S)(CO)~(,I~-C~H~)I

been

iI)

cvm

l’ragmciilatioi1

of the third

~-S)I(CO)O~‘-C~H~M~).:I

I .07, -0.33,

I’oI-III.

bridging

of‘ its phosphinideite-~~ll~p~~f

[ MoFeCo(/c

Multi-

isomcrization

irreversible.

Ph) W~IV irrr\crsihly

the lighter 12’) analogue.

specks.

that rapid

IILloFeCo(,l~-PR)(CO)x(~li-CjHi)]

Introduction

reduction

of the pho-

gave an isonm

The CV 01‘ the deproto-

;tnd electlochemically

with

have

two

seclucm

waves: the first wa\‘e w:as full>

to give the MO-CO

clusters and

quasi-reversible

nuctearity

q’-CjHj)]-.

clusters

(R = Me,

IOr the clusters

relati\,e

migration

17x.‘2” The ;III;I~O~OLIS tullgstcn-contaiiiili~

chalcogen-cnpped MoRu.

species

deprotonation

wa\‘e. however,

limuation,

PR)(CO)s(I15-CjH<)] potentials.“” The

induced

two oxidation

migration

is believed

lowing

MoFc.

thermally

to the formation

the second

of the trimctallic

tenipcratures,

ily

showed

vi3 11-PPh? bridge

undtmvent

and cationic

was established by ;I 4nglc-crystal that the jr-PPhz ligand bridges a MO-CO

~-CCI,H~M~-~)(/(-PPI~~)(CO)(,(

Ph. Ru’) w~1.s chemically

cliister

,,‘-C5H~)Jm

radical

bond, and aubscquent

and corresponded

Reduction Me.

and had

irreversible

of the radical

to the Co-Co

f’orm of this isomer

ple scanning

to

. an asaignmcnt

L+TISchemically

to give

co~lfimecl

study, which

phido

of [MoCo~(/1

Ph)

corrcspondcd

1-GeR)(CO)K(,~i-C5H5)]

process

oxidations

79). The

re\,crsiblc

jMoCo$/~

(R = Me.

(reversible)

[ MoCo~(lr;-CCr,H,Mc-~)(,~-PPh,)(CO)(,(

one-electron

tially

rlated

anion

of‘

of an ECE mechanism.“”

the characteristics The anion

voltnmmo~rams

IMoCol(lni-GeR)(CO)x(rli-C~H~)I

formation

rc\,crsible

and cyclic

waves. The tirst proccas

two reduction radical

127

Carbonyl Clusters

:steps, and

cluster

which

ha hcen clectrochemically studied is [ Mo~CO~(,I:-S),(C~)~(,I’-C?H~~~)!~. Recent work 01‘ Mansour rt rrl. showed that this compound undergoes ;I single. rc\,ersible. one-electron reduction at ~ I .04 V. a signilicantty more positive reduction potcntiul than that 01‘its electron-rich 62 CVE nitrosyl analogu~ [ hlolCol(,li-S)~(NO)~( I]~C~HJ3)~/

(-

I.53 V).‘j’

The clectrochcmistry

SK/i ;-S)2(C0)1(r15-CgH,Me)~I

was complicated

ol‘the

butterlly

cluster

IM~QCO~(/I~-

by an ~lectl-ode-sul-I‘LIct:

rcaction

“Very Mixed”-Metal

2e

x *

r

-I .30 v

that led to small spurious this problem anodic (Fig.

cathodic

wave at - I .63 V, behavior

sweep at -0.70

two-electron

wave

at -I

reduction

clusters

cores.

have

reversible

that can be explained

by an EEC-type

mechanism

[MoCol(Il3-II’-PBu’C(,HJ-2-PBU1)(/1-CO)(CO),(,I’-C.iHi)l

contrasting oxidation

observed

electrochemical wave

at 0.65

for the former

The sulfur-capped Fairly simple

waves

were observed

and O.Oc) V were

behavior;

V (E, = I80

cluster

electrochemical

processes. ;I third,

at - I.58 and -2.

irreversible.“’

The first two reversible

“quasi-reversible”

The oxidation versible

oxidation

containing

I I V, while

(-

at -2.23

for this cluster

clusters

II

at -0.

reoxidation

complex,

by four

at -2.04

though.

successive

by

An initial

oxidations

V). irre-

thought

being

studies

Et. Bu’).

the

centers

All

more

electron

combinations

ti~rmally

rich.

on the systematically

~7 to degradation

were

by lormation

results

processes

reduction cyclic voltammothree facile electron-transfer

clusters

correspondin,

The stability blc clusters

reduction

relative

reduction

curred in two some chemical was reasonably

dis-

one-electron

oxidation

V (reverse

IM~M’~(/LI-CO)~(~~-CO)J(PR~)?(,~~-C~HS)~~

panied

wave

The lower oxidation potential of’ the tungstento their molybdenum analogues is consistent with

by the electrochemical

M’(I)

;I quasi-

processes.‘3’

tLlngsten-containing

R = Ph. Me.

exhibited no oxidation

I. I I. - I .7 I V) were followed

is more

at 0. I6 V was followed

to be due to ECE

while

Reversible,

uncomplicated showed

reductions

reduction

behavior

the latter mV),

tetrahedral

[Mo2Ni’(/13-S)I(C0)7(I]i-C5HJMe)’l

behavior.

An of [ W,Co,(~;-S).~(CO)i(ll’-CSH-rEt)21

gram

and with

(up to 0.75 V).”

tetrahedral

played

tion:

.40 V. This to a reverse

80).“’

The

ters

V eliminated

at -I

.8S V that is coupled

[Mo7Co~(~3-~~2-PBu’C6HJ-2-PBu’)(~~-CO)(CO)~,(~~~-C~H~)~~.

was

- ,”

c

the reduction

a well-defined

by a further

fa\l

- x’-

-1.85 v

peaks; starting

and produced

is f’ollowcd

Ic

x’~ I

129

Carbonyl Clusters

trend

varied

was

underwent

an irreversible

of’ the cluster

into

identified

to M’(0) (confirmed

confirmed

tetrametallic

(M = Cr. MO, W;

electroreduced

of [ M(CO)~(q’-CjH5)]~

This

in one by IR).

clus-

M’ = Pd. Pt: tw+clectron fragments: step.

accon-

Oxidation

oc-

distinct one-electron transfers. with the second accompanied by decomposition. The radical cation generated by the first oxidation stable and has been studied by EPR as a IO6 K frozen solusuggested

that the HOMO

is located

on the metals

of the dications was dependent on the solvent, being [M1Pt2(/13-C0)2(~1-CO)-1(PPhZ)l(lj5-C5H5)2]

in the cluster.

with the most sta(M = MO or W).

130

WATERMAN

et a/

I’h,P

While

the reduction

tion potentials only

plays

potentials

were reasonably

;I limited

role

[ W2Pt2(/1;-CO)l(/l-CO)J[

CsHJMe)l]

(Fig. 8 I ). with

pendant

dation

wave

consistent

manganese

with

IX V. Oxidation

by a reduction

peak at -0.67

the EPR

rcsult~.‘“~‘~’

Mn(CO),(,,‘-C~H,Mc] displayed

In particular.

a single

analogue.

at -0.

cl‘t’cects. the oxidnthat the phoaphinc

metal centers,

was seen at - I .4S V (c.1‘. - I .U

appeared

followed

to R substituent Thih COLII~ indicate

PPh2CH,PPh2(

to its ldtriphenylphosphinc)

reduction

from

insensitive.

in the HOMO,

The related ilaritics

were scnsitkc

V);

of the cluster

an associated occurred

]7(/jisome sinirrevcr\ible rcver\e

oxi-

at 0.86 V and was

V in the rcvcr%e scan, thought

to originate

an ECE proccss.‘x

The anodic

scans of the three

C)(C0)2,(11”-CIHi)]‘. ?-mcthylallyl)] second

showed

almost

increased

completely

in theorcler

potential,

octanuclear

two oxidation

wavch.

irrcversiblc.

Oxidation

[ Re,Pt(/r~,-C)(CO)II(

(,lh-C)(C0)2,(1,1-C;Hj)]L~ large diffcrencc between state of platinum

relntcd

anionic

[Rc7Pt(,~(r-C)(C0)21(Mc);]‘~

the Iir\t

metal is Pt(lV).

in the cluster

with

and the

for the first proccsx

,~i-‘-methylallyl)]’

while

(Re,Pd(~r(,-

quasi-reversible

potentials

(0.42 V) < [ RqPd

(0.48 V) < [Re,Pt(,r(,-C)(CO)~,(Me)l]‘~ the latter two can perhaps be cxplaincd

in these compounds:

the capping

clusters

and ]Re7Pt(,(h-C)(CO)II(II‘~

(0.64V). The by the osidation

the highest

in the other clusters

oxidation

the capping

metal

is M(II).‘“’

D. Other Physical The electronic.

Methods

optical.

and magnetic

properties

of metal

clusters

are of great

current interest.’ but these properties have been little studied with “very mixed”metal clusters. This is to some extent 21 refkction of the difticulty of preparing high-nuclearity examples; many of these interesting properties become important

upon

increasing

cluster

size.

The

limited

magnetic

studies

to date

are

“Very Mixed”-Metal TABLE

in Section

Few other

studies

1II.D. I _. with complementary

ha\,c been reported.

gies of[RePt;(/l-dppm).~(CO)~]‘, dppnl)~(CO).J(S)]’ energies.

which

Sulfidation

platinum

The

limited

marid

at

mixed”-metal

an increase

XIII.

Re

along

when

measurements

carbonyl

clusters

(Fig.

group

the /I;-S

of “very behavior

and

groups

[ R~PL;(/I-

XPS

the

is thrmcd,

but

data

arc

o:ticlatim

at

are t’ormed.’

mixed”-metal ot’ mme

01‘ the

cner-

and [ RePtJ/lsuccessively

”

clusters

arc

~LIII~-

anti-lrromagnetic

X3) has been studied

dependcnces

IlI.D.2.

the aerics in Re 4f(7,‘2) binding affords

the Re=S

as

The magnetic

Temperature

in Section

the XPS binding

i-S)1(/1-dppm)i(CO);1’,

sulfidation

magnetic

in Table

~orhers.

reveal

oxidation

on subsequent

king

IRePt;(/li-S)1(~l-dppm)3(CO)-,I

[RePt,(,l

and

with

MO studies

one example

of IRePti(/l-dpptll)i(CO)~]’

dppm)l(CO);(S)]’ consistent

XIII

IShl S I L~t)ll:S01 VI.l
b~,\GNI:I

summtrized

131

Carbonyl Clusters

magnetic

“\cq

bq’ Pnsynskii

mcl co-

susceptibilities

x,,,

of‘

ICr2Cn(/~ ;-S)~(,~-SRL~‘)(CO)~(II-C.~HJR)~I (R = H. Me) have been detertnincd LISing the Faraday n~ethod.2’i.‘“i From x ,,,. the effective magnetic nmnentx /l,,t were calculated plots coupled WKI-acy ~ltts~s ited

using

fitted

the formula

~~~~~= m

. and plots of 11~1, vs T prepared.

the Heiscnberf-Dirnc-Mun

ions ICr(III).

spin 3/Z:

of’ the cotnpkxes

Co(I)

Vleck

(HDVV)

is diamagnetic]

in the ground

in eft‘ecti\,e

magnetic

moment

li)r two

in the absence

state. The related

[CrIM(IIJ-S)I(EI-SBLt’)(CO)(PPh.~)(,li-CiHs)21

;I decrease

model

of’ orbital

de-

phosphine-substituted

(M = Rh. II-) also with

The

exchangc-

tetnperaturc.

M/hi&

exhihagreed

132 with

WATERMAN the HDVV

nmdel.

In contrast

et al.

to the clus~cra

above.

the tetratnetallic

clulr~erx

ICI-IC~(,~;-S)I(CO)(,~~-<:H,R)~] (R = H. Me) were found to be diamagnetic x ,,, < 0). consistent with the I X-clcctron saturation of each metal atoni.‘4J.2”’ magnetic

susceptibilities

W) in solution magnetic value

tnomen~

merits

to I .39 ~~~~a( 40

the fact that these

The

C. The

clusters

to rationalkc

behavior

cluster

to an aerngc

( I .72 ~1,~). moliotonicallq

tungskn-nickel /r t3 at 40

At 30 C, the

corresponds

per molecule

cluster

C. These

are EPR-silent.

studied

bonding.

has encouraged

suggest

orbitals

structural

is prcscnted participated

111~

has magnetic

data.

in combination

tempcratitre-dcpcndent

(R = H. Mc)

tnent

[Crz(,l;-S),(,I-SBu’)(rli-CiHj)]~

(EH)

method.“’

atom\

with the chromium

Interaction

XIV.

rli-C5H~R)2]

(Fig.

magnetic In order

of the lower resulted

calculated lying

p-orbitals

and electromixed”-metal to determine

and metal-ligand

and [CrzCo$/@)(/13-

X3). the electronic has

d-orbitals

in Table

and

;I list of “very

in the tnctal~tnetal

of [ Cr1Co(/c;-S)I(/I-SBit’)(C0)2(

S),(CO)I(~ji-CgH~R)7]

data.

MO calculations:

by MO methods

chromium-based

interactions

cluskra

(M = MO.

of ten~peratures.‘4”

cquilibrin.

need

chemical which

electrons

of‘ I I9 /rt3 at 30 C and 0.03

sin,+-triplet

t15-CiHs).:(Ili-CsH~Me)I

over ;I tmgc

01‘ the molybdenum-nickel

of less than two unpaired

decreasing with

of [ MNi:(/l;-CO).;(

have been measured

(i.e.. The

structure

of the fl-ag-

by the Extended

Hiickcl

of the bridging

in the destabilization

ol‘the

sulfur

d-orhitals:

“Very Mixed”-Metal

the unusual portancc

ordering

of energy

of the 0-S

dichromium thought

ti-agment

to explain

C~HJR)J],

in contrast

For forming

Cr-Co

to participation

.04

this

MO

from

bridges with

of the

fragments

was

of [Cr~Col(/ll-S)(/r?-S)~(CO),(~~~which

orbitals.

with

unshared

is consistent

the in-

orhitals

with two COG

of half-occupied

sulfide

Bonding

the chromium

electron

pairs

the decrease

Icss than the sum or covalent

calculations

(/~-CO)(C0)2(11’-CjHj)ll as

resulted

half-occupied

possess ot’all

four

atoms

corre-

of the sulfur

atoms

in Cr-S

radii ol‘Cr

distances

to

( 1.36 A) and S

atoms.

Fenshe-Hall actions

because of the

a. significantly

A,

bonds

behavior

of formally

in “double-bonding:” ( I

< 6(d-d)]

use of four

to ICr2Co(,lj-S)2(,1-SBu’)(CO)Z(lj5-CgH~R)~1

properties

(s, p,. p,, and p,) orbitals

2.25-2.30

(S (d-d)

The

the diamagnetic

antifci-I-omagnetic sponds

levels

interactions.

133

Carbonyl Clusters

bctwecn

the latter

the odd electron

is effectively

pal changes

between

CI-~(BJH,)(,~‘-C~H~)~ and longer

(Fig.

Cr-B

acting

the ground fragment

distances

were

carried

8.1) in order Co(C0); as

on

[Cr2Co(,l~-)7h-B,H,) the nature

of the inter-

and Cr,( BqH,)( q5-C5Hs)2

;I cluster

“ligand”

state molecule in the cluster

and involved

out

to determine

(Cr2(B-IH8)(115-CjHs)ll

resulted

increases

to the former. in a shorter

in energy

Cr-Cr

I’ragments. The

princiand the distance

for those lingmcnt

or-

hitals which are Cr-Cr antibonding and Cr-B bonding. Interaction of an empty 0 orbital ofthe Cr(CO)j l’ragment with II tilled B-H-Cr orbital caused the hydrogen atom to become Cr-B-Co face-bridgin g. rather than edge-bridging.” In order to explain why the bridging vinylidene group of [ MoCO?(,I~-)I’-CCH,) (CO)s(q’-CgH’) cobalt atom,

I- (Fig. 83) leans toward the molybdenum atom ratller than a EHMO calculations have been employed. Results showed that the

134

WATERMAN

vinylidcne

capping

unit was particularly

the molybdenum

atom,

cial migration was shown

1 X3-273

The electronic

utilizing

in the clusters

in 1M$CO),( and

‘wd

hp,,

from

ha\,e ken

rl’-C.~Hi)~1

was rcali/cd \/ia ki,,

bridging

coordination

01‘ al I carbonyl

I I eV. while

the experinicntally ‘ill energy.-

greatest

(M=Mo.

group\

CO group.

W) (Fig. between

M=M

hetwccn

the orbitals

5d,:

co~~seqw~~ccs

coordinated

to M. into terminal

destabilization

fconictry

the

bonding

ha\ been con\idcrcd;

led to an cnergctic

ova

metal-metal

The energetic

bonds

determined

ol‘thc

Multiple

by o interactions

of ;I terminal

singlet

of the bonding

and Sd,, orbital.

barrier.

experimental

molybclcnLlm-bc,ncied

I‘ragments.

one of‘ the M-Rh

energy

NMR

The nature

in tcrn1\

with

Antara&

a sharp lncthyl

symmetry

calculations.

analy4

71 interactions ligand

with

cxhihitcd

and [Kh(CO)(II’-CiH~J]

interaction

tolerated.

ii large transition

is in accord

the higher

EHMO

of the step by step transl’ormation ;I carbonyl

by direct

is better

of [M~Rh(/I-CO)(CO).,(,j’-CiH~);I

structure

IM$CO)~(II~-C~H~)~I

Thij analoguc

K raulting

83) has been studied

charge

possessing

group,

disfavored.

the climethylvinylidelle

the range

weI1 stahili7ed

the positive

01‘ the C=CH? to be severely

data, where

bonds

where

et al.

01‘ about

w24 calculated

to h;I\ct the

binding

The calculated applied

EHMO

energy

levels for MzM>&

to [ Mol(‘o~(,l-r-S)(,(~-S)2(CO)~(

type cuhane

I&C~HJM~)J~

clusters

have been

(Fig. 8.1) in order to explain

bondinn ,s beh,lvior.“ It was suggested that the HOMO would ha\:c o(Mo-MO) ‘ ’ character and that the LIMO was most likely 0 (MO-MO): addition of electrons to the cluster

is hclievcd

by electrochcniical in [ Mo~CO~(/~~-S)(/I methods.” to I.57

IO result

studies

3-S)2(CO)4(

The total M-S for the M-/i

of electron\). /cJ-li~and rationale

The rather

sulfur

that overlap (60% )I.

of the MO-MO,

11l.C.).

q’-CsHj)2]

overlap

WIIC

population

than concentrated

/c4-S to metal bonds.

with

the metal

they

spread

in three

own’

bonds

ligands EHMO

four

is I.55 compared the s;mc M-S

distributions

the /I~-CO

have been

used

with the Mo atoms

the CO rr-syhtcnl.

The Ni-CO

to support

{-S)z( ,I’-CiH<)Jl 1(-1-,1’-coordination this assignment. “’ Orbital

were both o-bonding bonding

was

and Inulticenter

best described

numhel

bonds

in the

provides

the

ofthe

/i4-

the p-orbitals

The butterlly metal core of [ MolNi2(/~JU)(/1 a crystallographically contirmed carbonyl with calculations

using

in the 11 ;-ligand

[overlap

supported

studied

donate

It is primarily

cl-orbitals

a proposal of the sultido

to the /[J-S atom that

population

overlap

Bonding

has also been

;-S 1~ond.s (suggesting

for the longer

co-s

in cleavage

(see Section

MO-S

(40% ).

is bridged by (Fig. 83). MO interactions 01‘ bonding

as a dative

bond

with from

Ni to the 17‘ orbitals of the carbonyl. Low C-O overlap population rcllectod the additional electron donation into the C-O antibonding orbitals and was consistent with 2 low I’(~~). The bonding in [RcPti(,l-dppm)3(C0)It donation

01‘ electron

density

from

three

can

filled

he

Pt-Pt

understood bonding

in term\ orbitala

of the of‘ ;I Pti

“Very MIxed”-Metal (/l-dppm)3 ment

fragment

(or [ ReO?j’

bonding

and

cluster

electrons

dinatively

to the three

). In the MO

antibonding just

unsaturated

by selective

limiting

ionsaddat

dppm);(CO)~l.

I

o\:erlap

Analysis

although

are six

ot‘ this coor-

. but the latter

to two donor-acceptor

using

unoccupied

of I

the simplified

is weak.

the model

The

the Pt&lj-I)

six-electron

is cxpectcd.

cluster

[ RcPt;(/r-

[ RePtj(/l~-I)(I(-HIPCH7 The tilled

calculations

interaction donor

con-

[ReP~~(~~~-l)(/l-

niethod.7”

p, orbitals.

two

When

bonding

analogue

the EHMO

platinum

can XI as ;I wcnk

with

has only

bonds.

rhenium-platinLIm

of the interaction to give

the net bonding

Lmd that iodide

to form

and there

Reaction

[RePtj(/l-dppm);(CO);]+toyield

’ has been made with

frag-

combine

e symmetry.

MOS.~‘.““.“‘~‘~’

&. weaker

the Pt-,faceof

H~PCH~PH~)~(CO);]+ PHJ)~(CO)~]

aI +

donatin, ~7 to [Re(CO),]’ the interaction

pared to (RePti(jl-dppm)i(CO)J] Halide

with

of a [Re(CO);]’ orbitals

(53 CVE) with CO gives [RcPt~(/l-dppnl)~(CO)~]i The bonding may still be considered in terms

fragment

orbitals.

each

orbitals

the fragment

to rhenium.”

of 3 PI$jL-dppm)X acceptor

acceptor

fill the bonding

cluster

addition

vacanl

treatment.

MOs

which

135

Carbonyl Clusters

I>-orbital\

of that.

suggest

is covalent

in nalure

by using all its filled /I-orbitals

in bonding. In order EH

to study

calculations

bondin

have

OH)(CO)~(O)(PH;)JI acter

‘.“’

in the central

ripheral

g in IR~P~s(/~-O)~(~.~-OH)(CO)~(OR~O~)~~’C~~),I

been

carried

met&metal

on the model

Calculations

Re-Pt

bond.

bonds.

;uid the very unusual

out

indicak

with

data

su ggests

show

a degree

triple-bond

char-

due to the prcsencc

of’ pe-

;I very

short

of multiple

in [RePt.i(/r-O);(/l-OH)(CO)~(OReO;)(PCy;),I

‘.

IRePt5(/r-O);(/l-

at least ;I partial

complicarions

Structural

structure

clutcr

Re-Pt

metal-rnctal

‘. consistent

with

distance bonding

the thcorc~ical

result\.

IV CONCLUSION With

flexible

systematic tution

routes

into “very

investigations

generally

proceeds

with

not site-selective;

many is often

twined. Characterization which generally results spectroscopic

studies

of C-Ii&and

this involves of heterometallic

mixed”-melal

of their reactivity

one configuration

amplcs

AND

OUTLOOK clusters

and physical

metalloselectivily.

oE these complexes sufficiently

stable

in hand. the time is ripe fat properties.

Ligand

but the reactions are highly

fluxional.

so that mixtures

substi-

are l‘rcquen~lq and more

of’ isomers

than

are ob-

of these configurations has largely been crystallographic. in one configul-ation only being identified: comprehensive are needed

to identify

transformation

a heterometallic centers

all confgurations.

have been reported bond

in effecting

or fact.

This

likely

the transformation\.

A number

and. in almost indicates

of ex-

all instances. the importance

but mechanistic

studies

136

WATERMAN

to confirm

this remain

all instances.

ters with

“very

mixed”-metal

metal combinations

Re-Pt

of clusters

mixed”-metal

to stabilize catalysis

the resulting

in hcterogencouc clearly.

there

have been intensively

has yet to he fully

in controlling

optical

properties)

importance

ligand

exploited.

mobility

are almost

catalysis is great

untouched.

v ABBREVIATIONS

arphos

I -(diphenylarsino)-2-(diphenylphosphirl~))~th~ll~

C

coulometry

cod

I.5cyclooctadiene

CV

cyclic

CVE

cluster

DCP

d.c. polarography

voltammetry valence

electrons

dmat

3-(dimethylethylarnino)loluenc-C,

dmba

dimethyl

N

henzylamine-C’-N

dmpe

I .2-bis(dimethyIphosphino)ethanc

DPP

differential

dppa

bis(diphenylphosphino)acctylenc

pulse polarography

dPPC

I .2-hia(diphenylphosphino)cthanc

dwl ECE

bis(diphenylphosphino)mcthanc electrochemical-chemical-electl-o~ll~l~li~~ll

EEC

electrochemical-electrochemical-~helni~~ll

ETCS EXAFS

electron cxtendcd

tran~f‘cr-catalyzed x-ray absorption

synthesis tine structure

HDS

hydrodesulfurization

Pz TEM

pyrarolyl transmission

THF TPD

tetrahydrofuran

TPR XANES

temperature-ploframtned reduction x-ray absorption near-edge spectroscopy

XY

XYlYl

electron

tcmperaturc-programined

only

microscopy desorption/decomposition

in In-

by clus-

(e.g., MO-Co

scope

properties

01

The sig-

electrochemical

properties These

in

for exploring

recently.

and tuning

physical

in the future.

APPENDIX:

unlikely

and that the fragments.

The physical

studied

and other

though

on the cluster,

have been dominated

with other metal combinations.

clusters

ofheterometals

of increasing

center

reforming);

nificance

nonlinear

possible.

elsewhere

cluster

effective

in petroleum

response netism.

occurs

unit is the favorable of”very

the potential

out; it i.s always

that the transformation

heterometallic vestigations HDS;

to be carried

et al.

(c.g..

are likely

magto be

“Very

Mixed”-Metal

We thank the Australian Research Council Poqr&mte Awrd. imd M.G.H. :icknowledpe\ Senior Research Fellowship.

Carbonyl

Clusters

137

t’or support. N.T.L. is the recipient of an Australian :m ARC Auhtralinn Rc\earch Fellowhip and :m ARC

Rl
(3) (3) I5 I (0) (7, (8) (9) ( IO) (I IJ ( I3 ( 13) ( IJ) ( IS) ( 16) f 17) ( IX) ( 19) (20) (2 I ) (22) (2% (2-t) (25, (26) (27) (18) (291 (30) (3 I J (32)

Srone. F. G. A. &w. (‘lwrr.. /,I/. U. Ei~,r/. 19X4, 22. X9. Vahrcnhwnp. H. C‘~urrwur.\ /JIO,;~. Clw~r. 1985, 4, 251. V;lhwnkanlp, H. &h: O~;~ouww/. Chw. 19X3, 22. 169. Mingos. D. M. P AX. (‘/w/u. Kc\. 1984, 17. 3 I I. Holf‘mnnu, R. ,I/I,~~,I\: c‘l/c/,/.. //I/. EC/. Fl,q/. 1982, 2/. I7 I I. Gtadfelter. W. L.: Geoffroj. G. L. iIth: O~,q0/fofrwr. Uwrr. 1981, lx. 207. Farrugia. 1,. J. In (‘~,,,r/‘,~/rc,,~ti~,~, O,;~r,fr~,/l~c,trr/lic, C/wri.\rv\~ II: Abel. E. W.: Stone. 1;. G A.: Wilkinwn, G.. Eda.: t’qwnon Prw: Oxford. 1994. Vol. IO, 0. 4. Chi. Y. In C‘or,~/,~~,he,r.\i~,eOl;~or~l,ff~ctrrIlic ~/~~wi.~f~~~II: Ahel. E. W.: Stow. F. G. A.: Wilkinson. (;.. Etly., Pergnmon PI-~\\: Oxtiwd. 199-I. Vol. 6. Ch. 3. Br-rice. M. I. J. O,~i’c/,r~~~wr. C/w/,r. 1983, 2-V. 417. Koherl\, D. A.: Gcot’froy. G. I,. In C.~,r/r/“.~,/rr,lti~,c 0,;9~,rllfr,rcto//;[, clw,,~i.\rr~: Abet. E. W.: Stone. F. G. A.: Wilhlnson, G. Edg.: Pcrgamwl Prcsh: Oxford, 1982. Vol. 6. pp. 701. C’owlock. M. <‘.: Sh:rplcy. J. R. c;wri/. (‘hcu~. /?<,I: 1995, I-l.?. XII. %pp;~, E.: Tiripicchio, A.: Brwwtein. P. (‘oo~r/. (‘/wu~. Kc\: 1985, 65. 2 IO. V;ihl-cnk:mq H. P~~IP /I/>/I/. C’/w,rr. 1989, hl. 1777. Clark. I). T.: Sutin. K. A.: McGlinchq. M. J. O,~f,,l~,,lic,r~,//ic,\ 1989, 8. 155. Sutin. K. A.: Kolih. J. W.: Mtekw. M.: Bouseard. P.; Sayer, B. G.: Quilliam. M. A.: Faggiwi, ii.: Lock. C. J. L.: McGlinchey. M. _I.: J;~ouen. G. O~~o,fl,,,rc~tc///i(,\ 1987, h, 339. Jcffcry. J. C.: Lawcnce-Smith, J. G. ./. O~;qr~~wwt. C‘lwr. 19X5, 280. C31. C’hercurl. M. J.: Chetcuri. P. A. hl.: Jefl?t-j. J. C.: hlilts. R. M.: Mitrpi-achachon. P.: Pichering. S. J.: Stow. F. G. A.: Wood\\;lrd. P. .I. (‘/~/JI. Sot. /I~//cjrt 7>0,,,. 1982. 699. Dunn. P.; Jcffery. J. C., Shet-wwd. P. ./. Ogwrwrw/. Clwur. 1986, .{I 1. C5S. Scou. I. D.: Smith. D. 0.: Went. M. J. ./. CI,c,ir. Sock.. /Ici/tr,,r T,.c/r~.s.19X9, 137.5. Jct’t’c~-y. J. (‘.: Rut/. M. 4.: Stone. F. G. A ./. C’/rr,u. .(‘.: C‘hcn. S.-N ; Warlf. X.: Sun. W-H.: Wang. H.-Q.: Y;mg. S.-Y. /‘i~/~lwt/nu~ 1996. 1.5, 2613. Miiltcr. hl.: Schachr. H.-T.: Fiwher, K.: tm\llng. J.: Ciiitlich. I?: V;lhrenknrnp, H. /rw,:$. Clwut. I’lm~idt~. R. P.; V&c-enkamp. H. O,:i’r,fior,,~,~r//lir~.v 19X7, 6,. 492. t3eurich. H.: Btumhot’w. R.: V~lhl-cnharnp. H. C/~/II. Hc,/: lY82, //5. 2409. l3lun~t~o~cr, R.: V:ihrenkanip. H. C’lwrir. /fc,/: 1986, I/Y, 6X3. Schachr. H.-T.: V:~hrcnhamp. t1. Ch~wr. Nc,,: 1989, 122. 7239. Mnni. I).: Sch;lchr, H.-T.: Powell. A.: V;ihrrnkamp. H. O,~[/lr,,rrrrrlr//;~,.\ 1987, 6. 1160. <‘urno\L. 0. J.: Kmnpf. J. W.; c‘urti\. hl. II.: Shen. J.-K.: Bnwto. F. ./. ;tw. (‘lwur. .%,c,. 1994. Ilh. 221.

138

WATERMAN

et a/

“Very Mixed”-Metal

Carbonyl Clusters

139

140

WATERMAN

et a/

“Very

Mixed”-Metal

Carbonyl

Clusters

141

142

WATERMAN

et al.

“Very Mixed”-Metal

Carbonyl Clusters

143

ADVANCES

IN ORGANOMETALLIC

CHEMISTRY,

VOL. 46

Friedel-Crafts Alkylations with Silicon Compounds IL NAM JUNG

and BOK RYUL YOO Organosikon Chemistry Laboratory Korea Institute of Soence & Technology Seoul 130-650 Korea

I. II.

tnt1-oduction Characteristics of FI-~edel-Crd’t~ Alhylation\ with Silicon ~on~potmd~ A Renclivitm and Mechmim. K. Orientation and Iwmcr Diwihution\ ........... c Tran~~~lkyl~~tion\ and Reorientation\ ... I~ricdel-Cc-aft5 Alkylation of Areneh with AIh~~~ylchloro\ilane\ ............ ;I. Alkylation with Allylchlot-osilnnch H. AIhylntion uith Vi~~ylchloro~ila~~~~ .............

III.

IV.

Iso I.50 I .io 1x8 I65 165 I (1’) Il.3 17x I78

Ft-id-Ct-aft\ Alkylntiom of At-cneh A ith (C’hloroalhyl)\il~~n~~ ,\. Alhylation with (cr,~(‘hlol-oalhyI)~il~une~ .......... .......... I3 Alhyl;ltionwth tf~ichloroalh)l)\ila~~~~~ .......... c‘. Alhylation ~ith(Trichlol-onlcthyl)hilall~\ (‘onclu\ion and Prospect\. ................. Rcicrcncea. ........................

V.

I INTRODUCTION Friedel-Crafts quite tion

some

alkylations

titne

and

of benzene

by Friedcl pounds

with

and Crafts

much amyl

introduce pounds

work

halides.

was

substituents

first

described

In the following dcrivatives

done

have been studied

in this

field

amylbcnzene

Friedel-Crafts

onto

(phenylethyl)trichlorosilanc,

acids’-”

to produce

alkenes.

and the petrochetnical alkyl

by Lewis

has been

chloride

in 1877.‘,3

such as organic

laboratory

catalyzed

alkylations

and alkynes

industry

as valuable rings.’

with

6’1 (11. in

a monotner

that was hydrolyzed

reported

1953,

with

by Wagner

year, Petrov

organic

the Friedel-Crafts

for

routes

silicon

to

cotn-

the preparation

01‘

to polysiloxanea.’

alkylation

At that time. the silicon

com-

used in the

and established

Alkylation

the rcac-

was first reported

are now widely

aromatic

with (chloroalkyl)silanes.X

since

for

industry

of benzene was gt-ow-

ing rapidly and supplying monomers on ;I large scale by the direct synthesis ot organochlorosilanes, a process discovered by Rochow.” Alkylations with silicon compounds such as alkenylchlorosilanes’O~ I3 and (chloroalkyl)silanes’4~“’ were expected

to be a way

and a few articles Fricdel-Crofts

of preparin g useful monomers for polysiloxane products. on this topic were published by 1968. 10~20 Soon after, interest in

alkylations

with

silicon

compounds

faded due to the difhculties

of

145 Copyright ~12001 by Academic Press, Inc. All rights of reproduction in any form reserved. 0065-3055/01 $35.00

146

JUNG AND YOO

the syntheses

and separations

ofalkenylchlolosilancs”.”

and (chloloalkyl)chloro-

silanes.‘3~‘4 In 1993, a successful and ally1 chloride tives lalion

using

direct

synthesis’”

gave us a motive

allylchlorosilanes.‘”

of various

aromatic

and naphthalencs lysts. This

work

with

We hale compounds

This matic

rcvieu

will

describe

compounds

catalyzed

rainvestigated

allylchlorosilu~ies~f’

wilh

alkylation

the chemistry silicon

deriva-

the FriedclPCr;tfts

alky-

hcnrencs.

with

progrcs\

of this intcresling

01‘ Lewis

has been

ol‘ the Friedel-Craiis in particular

biphcnyls. acid

cata-

vinylchlorosil~uics~‘.~’ macle in the dc-

class of orgnosilicon

compounds.

metal

of benzcnc

iii the presence to alkylation

Substantial

of the chemis&y

h-om silicon

the alkylation

SLICK as substituted

has also been extended

and (chloroalkyl)chlorosilanes.‘” velopment

ofallyldichlorosilane

Ihr exploring

compounds.

alkylation

the aluminum

of arochloride

reactions.

II

CHARACTERISTICS OF FRIEDEL-CRAFTS WITH SILICON COMPOUNDS In this section. alkylation

the rcactivities

of aromatic

and the mechanism orientation

compounds

compounds

in the presence

01‘ the alkylation

reactions

and isomer

as the decomposition

oforganosilicon

distribution

and reorientation

and the insertion

reaction

chloride

be discussed. Lund associated

to chlorosilancs.

of alkylatcd

01‘ allylsilylation

for the FriedclKM’ts

of aluminum

will

in the products

ot‘ chloroalkylsilanes

as trunsalkylation

ALKYLATIONS

products and other

will

along

caMyst with

the

problems

such

Side reactions

such

also be mentioned.

related

reactions

will

be

explained.

A. Reactivities

and Mechanism

The reactivities ofalkenylsilancs in the presence of a Lewis acid vary depending upon the nature of substituents on silicon as shown in Table I. in the presence of aluminum chloIn the cast of alkylation usin g allylsilancs ride as a catalyst, allylsilanes the silicon react with aromatic to give alkylated

products.

2-q-

containin, o one or more chlorine compounds at room temperature I -silylpropanes,‘”

while

substituents

on

or below

0 C

allyltrimcthylsil~une

did

not give the alkylated product but instcad ditnerized to give the allylsilylation product. S-(trimcthylsilyl)-4(trimethylsilyltncthyl)I-pcntenc (Eq. ( I )).30 In the alkylation rcaction, the reactivity of allylsilancs increased as the number of chlorine

Friedal-Crafts

Alkylations

TABLE

atoms

on

the silicon

increased,

147

with Silicon Compounds I

but decreased as the number of methyl

go-oups

in-

creased. SIMe, .CI,,

(Friedel-Crafts

alkylatlon) ME!

AICI, Cl, Me, Si

t Me ,SIHMe Me (allylsilylation)

Alkylation with vinylchlorosilanes requires a relatively higher reaction tcmperature and prolonged reaction time. likely due to the lower stability of the carbocation intermediates. It is well known in the literature that aluminum chloride, a strong Lewis acid. is a very effective catalyst in Friedel-Crafts alkylations with silicon

148

JUNG AND YOO

compounds,7.“.l”~‘“.~“~‘S

chloride action

21 small

amomit

of anhydrous

aluminum

initiates

the reaction.3’

reactants with

In the Friedel-Crafts

catalyst.

air

the r-bond

,f7 to silicon.

bilizcd

This

by the electron-donating

/~-stabili~ation’~~~~ through

protonation

on the aromatic the catalytic

scribed

above.

facilitates

group carbon

the protonatcd g silyl

of aluminum

which

intermediates

silicon.

than protodesilylation. give higher

yields

The substituent activity

which effect

the aluminum one

compared

is similar

not react with

chloride-catalyrcd chlorine

the co-

is largely

retarded

of the clcctroncgativc

undergo

alkylation

show higher

fasta

reactivity

to that of allylsilanes.

01‘ methyl

atom

groups

xd

with

atom

However.

products.J’

allylsilancs

on the silicon

The rc-

on the silicon

increased.

to gi\,e alkylatcd

of arenes

substituents

chloride

;I Me;SiCI-AICI;

” “’ In contrast.

ol‘ chlorine

benrcne

alkylation

for al-

to allyltrin~ethylsilane.~”

as the number

as the number

dots

or more

intermediates

than

and

to the presence

due

cation

of vinylsilanes increased

but decreased

vinyltrimethylsilane

of alkencs:

cm

as de-

by hydrogen

gi\,cs propcne

is why ~~llylchlorosilancs

in the alkylation

of vinylsilancs

increased.

The

cation

on silicon:“‘This

groups

for allylchlorosilanes

col?jugation

m-,7

chlorine

on

which

initiates

[j-stabilization

ol‘allyltrin~ethyIsilane

a-

a cation

silylalkylated

tar allyItrin~cthylsilane

the allylsilylation

cation

due to less et’t’cctive atom(s)

I -silylpropyl

g methyl

:I\

is gcncrated

This proton

intcrmediatc

effective

chloride

catalyzes

to give

through

the

is sta-

Elcctrophilic

alkenylsilanes.

of the electron-donatin

m

ring generates

with

group

in the interacts

known

ion

of a proton.

alkylation

the re-

cation

conjugation

01‘the ally1 group.”

the regeneration

be more

can

because

lapse of the fi-silyl

0-7~

carbcnium

by deprotonation

is follo~~ecl with

chloride

silylethyl

which

the protodesilylation”‘.‘“.”

complex.

through

secondary

from present

ion intermediate

the intcrmediatc

stable

of the Friedel-Crafts

This

in the presence

silanes.

silyl

by the electron-donntin

lylchlol-osilunes

hydrogen

of the aromatic

01‘allylsilanea.

In the case

be stabilized

inevitably

ion on the n-bond along

cycle

from

with aluminum

resulting

to give the carhenium

the more

ring.’

ol’arenea

chloride

moisture

proton

because

of the terminal

compounds

with

The

occurs

and

tack of this carbcnium aromatic

chloride

of alkenylsilanes

carbon

alkylations

of hydrogen

In

or vinyl-

of silanes

are

required. The reactivity of(w-chloroalkyl)chlorosilanes for the alkylation ofarenes varies depending upon the length of the w-chloroalkyl group and the substituents on the silicon. Generally, the reactivity increases as the length ofthe alkyl group on the silicon of (try-chloroalkyl)chlorosilanes That

may

silanes

be mainly

and the aromatic

attributed

ring. and partly

The rearrangement of alkylating and chloride exchange between known.’

These

indicate

increases to the steric

from

methylene

hindrance

to the electronic

to propylene.“.”

between nature

the incoming

of the silyl group.

agent under Friedel-Crafts reaction conditions aluminum chloride and alkyl chloride are well

that the alkylation

proceeds

via the transitory

existence

of

Friedal-Crafts carbocations

resulting

Alkylations

149

with Silicon Compounds

from complexation

between

the alkylating

agent and Lewis

acid catalyst. AICI-, Brown

and Grayson

reported

chloride

was

in AICI;,

and first order

third

nucleophilic chloride ionization

The ing upon

of

acid catalysts.

differences

The ratio

indicates favors

group

of

bulk

probably

solely

by an

by the rate

of the concentration the alkylation.

777rt~7

COLIC

position

od7o

or alkylation-dealkylation

adducts

predominantly.

atoms.

the 777~~~7 isomer and/)at-ll isomers

ol

derived

the Lewis from

Considering

interaction

hindrance

the

benzenes.

increases

reason

from for the

The yield ol‘the

as the reaction of aluminum

are the kinetically r77m7

between

arising

may bc the principal

of the resulting

stable

of halogen-substituted

/MM

Steric

in the presence

or-t/w and /IO/X adducts more

to the steric

substituted

777~~~~7 isomer

temperatures

the thermodynamically

at

dependence

with

ally1 groups.

rates oithe

and that of the

or at higher

that the

at the

arc obtained with

products

pc77‘~7

of

deprnd-

on the benzene

products

of the products

and

mixture

varies

allylsilanes decreases as the size of No o,-r/7~~-~~lkyl~~ti~)r~products increases.“.”

and the incoming groups

products

due to the temperature

benzenes ring

an isomeric

of the substituents

reactions

to the

wfho

gives

of the alkylation

isomerination

in the alkylation

The alkylation

ortl7o

and steric

on the benzene

and isomeriLation

proceeded

undergoing

of isomeric

in the case of isopropylbenzene

decreases

long periods

order

chloride-aluminum

bc independent

compound

ratio

distributions

temperatures.

the size of the alkyl isomer

nature

and/or

the subatituents the isopropyl

polar alkyl

benzyl

first

rate determining

;I

be determined

henzenes

The

of monosubstituted

are obtained

a

that

If the reaction

should

and

of the aromatic

isomeric

formation

alkylation

on should

monosubstituted

the electronic reaction

isomer

chloride

/“/rlr-products.’

and

Different

different

component

indicates

in the alkylation.‘”

with

component,

and isomer Distributions

alkylation

o~~~/w. ~ttr,

This

the rate ofalkylation

reactions

in aromatic

chloride.

by the aromatic

propel-tics

B. Orientation

first order

in benzyl

of the alkyl

or nuclcophilic

R’AICI,

that the rate of alkylation

overall:

is involved

mechanism,

of ionization

ring.

order

attack adduct

+ RCI -

proceeds chloride.

ortho fat This

controlled

products

alkylated

benzcnes

product.

benzenes

with allylsilanes

the high

gives

electronegativities

ortho and of halogen

was expected to be the major product. The predominance of in the products indicates that the resonance effect of halogen

substituents lo the benzene effects. ‘(’ The isomerization

ring should be considered in addition of the products from the alkylation

is faster than that of the products

obtained

from

the reaction

to their electronic of alkylbenzenes

of halobenzenes.

150

JUNG AND YOO

C. Transalkylations Alkylation onto

and Reorientations

of benzene

the ring.

Di.

tri.

does not stop with and

higher

production

of higher

ing a molar

excess of benzene

The alkylation

alkylation

of benzene

of aluminum

chloride

the introduction

alkylation

compounds

product5

bc controlled

can

and by variations

with

temperature

than the 1.3.5trialkylated silylalkyl

compound

peralkylated

with

product.

less alkylated

gave no higher

due to higher

LIS-

parameter\.

alkylation

proclproducts

steric interactions

among

the

groups.

It is also from

with allylsilanes

by

in the presence

for 4 h gave along

The

extent

SOII~C

excess vinylmethyldichlorosilane

at room

the alkylation

to

group

produced.

in other experimental

hexakis[2-(methyldichlorosily1)ethyl]benzene.” ucts. However.

ot’ one alkyl

are also

well

known

one position

aromatic

ring to another

The intramolecular intermolecular processes

that

alkyl

to another through

alkyl

transfer

can

be transferred

ring

and intermolecularly

dealkylotion

alkyl-transfer

arc normally

groups

on the same is called is rcferrcd

reactions reorientation

cataly7,ed

intramolecul~lrlq from by Lewis

or isomerization

to as disl”up(~rtionation.

one acid.

and the

Reorientation

faster than disproportionation.

FRIEDEL-CRAFTS ALKYLATION OF ARENES WITH ALKENYLCHLOROSILANES This

section

hydrocarbons as

will

ally1 and vinyl.

on silicon

describe

The reaction

containing

will be discussed

alkylation

reactions

short chain alkenyl

of aromatic groups

in terms of the suhstituent

such effect

and the urene rings.

A. Alkylafion

with Allylchlorosilanes

Nametkin and co-workers with allylchlorosilanes in 2-(Aryl)propylsilanes (Ph-X:

the Friedel-Crafts

with alkenylchlorosilanes

tirst reported the presence

were obtained

from

the alkylation of aluminum

of benzene derivatives chloride as catalyst.”

the alkylation

of substituted

benzenes

X = H, Cl. Br) with allylsilanes such as allyldichlorosilane and allyltrichloI’-.” The yields ranged from 34 to 66% depending upon the substituents

i&lane. on the benzene ring, but information distribution was not reported.

concerning

reaction

rates and product

isomer

Friedal-Crafts After

succeeding

tncntal lung

silicon

Alkylations

in the direct

with

;I mixture

rt nl. reinvestigated

allyldichlorosilanes

synthesis

of allyldichlorosilnne

of ally1 chloride

the Friedcl-Crafts

in detail

151

with Silicon Compounds by reacting

and hydrogen

reactions

chloride

01‘benzene

ele-

in 1993.‘”

derivatives

with

(Eel. (2))

X = H, Me, Cl R’ =H.Me R’ = halldes. alkyl, Ph. OPh. etc

The results

ofthese

ot‘aluminum As shown

and

lation.

with

obtained electron

donating

lltcilitated

the t-eaction.JJ’.J”

ulkylation

reaction.

The reactivities

on the substituents

chlorine

tltoms

lane, readily

in the presence Among

with

ride catalyst

I‘rom 70 to 78%‘. The results deactivated

groups

on benzene

the electrophilic

l’or the alkylation ofbenzenc Allylchlorosilanes benzencs

chloride,

fI-otn 60

temper;ttures the alkygeneralI>

nature

of’ the

derivatives varied dehaving more than Iwo and allyltrichlorosi-

to give I?-(aryl)propylchlorosilane~

but allyl~ritnethylsilane

did

not react.”

allyl~richlorosilanes ga\‘e the highest yield while higher reactivity for gave the lowcst,47 thus indicating

substituted products. of aromatic in good

with

temperalure

ranging

at lower

such as allyldichloron~ethylsilant:

allylchloroditnethylsilane

the alkylation

times

such as halogens

such as alkyl

is consistent

substituted

of aluminum

Monoalkylation

I at room yields

on silicon.”

the allylchlorosilanes,

the polychlorine

This

on silicon.

reacted

took shorter

groups groups

ofallylsilanes

pending

good

20 min at 0 C ranged

that electron-withdrawing while

( I) in the presence

II. with

in relatively

alkylbenzenes

within

in Table

of halobenzenes

the monoadducts

The reaction

indicated

with allyldichlorosilane

are summarized

II. the alkylation

uffot-ded

the yields

reactions

catalyst

in Table

l’or SO min to 66%.

alkylation

chloride

isolated

allylchlorosilanes. 3-q-

I, I -dichloro-

compounds yields

with (60-X0%)

I -silabutanes.

1 in the presence along

with

small

alkylation products. Dialkylation products were obtained 2 (o 8% when a S-fold excess of the aromatic compounds used. The amount ofdialkylated products excess of the aromatic compounds.

can be further

were obtained of aluminum amounts

from chlo-

of highet

in yield5 ranging from with respect to I was

reduced

by using ;I greater

In the alkylation oftoluene at various temperatures ranging from -45 C to room lcmpcrature. different product distributions (o-: 777~:,w) were observed ranging frotn

152

JUNG AND YOO TABLE ~I.KYI.AI‘ION

(‘ONIXI

IONS” 4UI) I’ROI)M’l

H

1-t

H Ii Ii H

rt

53:9:38

at -45 indicate

of the methyl

0

thermodynamically of toluene with reported

0 0 r1 II 0

;lc:hh = 62.3X ah:bc = 2% ah:hn = 80:70

0 0 0

C to I7:20:63

at 0 C and

that the alkylation group,‘”

the isomerization

at an early

1 decreased

to 3:65:32

of the benzene due to the stage

or alkylation-dealkylation

at I-om

ring with

temperature. 1 produces

catalyst

for intra-

Then

of the alkylated

substituents

on benzene

nature

at a later

benzenes

and intermolecular

products. ortho- to the IW~CI- and /xrrtl-products

as the size of’the

These

kinetically

ortlzo- and pal-(r-directing

of the reaction.

more stable rnptn-product, as had been observed rl-butencJU Aluminum chloride in Friedel-Crafts

to be an effective

of the alkylated The ratio of

01

3 I :2:h7 27:(,:67 29:9:62 \:h6.3 I ‘1:(13:.U m.i3:(,7 m:37:hi 47:3:5I)

II

ortho- and patqxoducts,

controlled

t~lSl‘KIHIII’ION

s

1‘1

Ii H I1 H MC MC MC MC

results

II tSOhll~l<

the

in the reaction reactions was

isonlerizations’“.5”

of monoalkylbenzcnes ring

stage.

favors

increased.

with No

ortho-

alkylation product was found in the case of i-propylbenzene due to the steric arisinteraction between i-propyl and the incomin g ally1 groups. Steric hindrance ing from the size of the alkyl groups at ortho positions of the substituted benzenes appeared

to be the principal

cause of the differences

in isomer

product

ratio.44.“5

Friedal-Crafts The yield ofortho-isomer ceeded

for longer

Alkylations

decreased

periods

and mpfa-isomer

or at higher

153

with Silicon Compounds increased

temperatures

as the reaction

in the presence

pro-

of aluminum

chloride. The

alkylation

of halogen

atoms

are orflu)-

itiea of halogen Higher

and l?crm-directing the r~ttr

atoms,

resonance

effects

that the alkylation faster

Isomerization

of the products

those of the products Substituent

effects

with

I were studied

rized

in Table

obtained

of the benzene by comparison

from

might atoms.

H F (‘I HIMl2 Et I-PIPI1 PhO /‘A7 II-Me f/l-Me /‘-Me

I .oo 0.08 I 0.0 I6 0.01 I 3.X’) 1.10 5.6s 10.37 9.-L?

--

product.

he responsible The results

benzenes

group-substituted alkylbenzenes

for

indicate

with

1 was

bcnzencs.“.i’

was also faster

than

halobenzenes. ring with

in the alkylation benzene

itself.

of benzene These

111.

H H H H II H H H H MC MC Me hlr

I results

the high electronegativ-

g group-substituted

withdrawing

with

that the halogen

to bc the major

effects

of the halogen

obtained from

Considering

to electronic

donatin

of electron

benzenes indicating

was expected

properties

of electron

than the reaction

(9 I-98%).

groups. isomer

compared

ortlro- and /,ul-n-directing

the

(R = F, Cl, Br) substituted

orttho- and p(l)-(/-adducts

in predominantly

0.00 ~ I .01 -1.34 ~ I .C)h 0.59 0.6 I 0.72 I .o I 0.97 I.12 0. I3 0.x 0.05

0.00 0.74 0.72 0.72 -0.OI --0.02 0.2s 0.76

0.00 -0.60 -0.21 - 2.52 4.JI -0 44 -~ -0.?7 -1.39

results

derivatives are summa-

154

JUNG AND YOO

The reactivity

of substituted

R =

Ph > PhO

alkyl

henzenes

halogen

ben~enes,

the fastest

for bromohenzenes,

substitucnts

electronic

effect

plotted

against

According

of substituted substitucnt

11 was found

coefficients zenes with

respect

the reactivity

for alkylation

/~trmxylcne In order

to study were

products

increased

increased.

decrcused

k,JkH = pm.

and

the electronega-

where

effect

of

0 is ;I Hammet

between

rates for the alkylation

the substituent

of substituted

In the case of disubstituted

as follow:

Illrttr-xylem

rcuction

of bcmenc

the polyalkylation

carried

was carried

chloride

uct. The reaction afl’ordcd

dialkylated

various

ben-

benzenes.

> o,//~o-xylene

obtained

to obtain

;I 7-: I mixture products

trialkyluted

>

with

derivati\,es. The

to hcn7ene

points.

ol‘ allyldichlorosilanc (12~31% ) alon g with

usin g ii 3: I mixture

Thus.

derivatives

products

derivatives wcrc

the reaction

in the presence

as the major

prod-

and ben7cne derivatrialkylated products

of nllyldichlorosilanc

were obtained

alThe

polyalhylated

to bcnrene

from the one step reaction

dialkylated

con~l~~unds

derivatives

benrenc

conditions.

~LIL‘IO their high boiling

(Eq. (3)). In the reaclioii dcrivntives.

with

reaction

allyldichlorosilanc

catalyst

using

rcncted

ratio of allyldichlorosiI~unc products

by distillation

out by adding

of aluminum

was

out under

its the mole

but the polyalkylated to purify

benz.enc

with

that the rcsonancc

the relationship

reaction

allyldichlorosila~~e

reactions

(23-?X’%)

for Huorobenzene

> /“f~~/-‘hl0r010lLiene.

lylchlorosilanea.

diflicult

log

I flom

(lo g kIJkH).

to benmie

the

with respect to benzene (log kK/kll) were (a) a’ for alkyd, aryl. and halogen c~mups.

equation:i’

(0) and the relative

indicate

of

Among

bermme\.

sho~~ld be considered in addition to the -I(> the reaction rates. The relative reaction rates

bcnzencs

to be -3.

substituted

order:

alkylation

ring

coefficients

to the Hanmet

constant,

in the I’ollowing

was not consistent

The results

to the benzene

decreased

rutc was observed

which

in order to explain

for the alkylation

(Ph-R)

> H > F b Cl > Br.‘” The

than that 01’ halogen

of the substituents.‘f’,“.52

halogen

tives

benzencs

> Et > Me

was faster

substituted

the slowest tivities

> i-Pr

as the nlajor

hind product.

Cl ‘sl H

AI&. RT -I::::

1

R = H, Me, Et. iPr

I’

‘cl -i

R

‘sl H

I/AK&, RT

‘cl

R= R= R= R=

H; n = 1 (41%), n = 2 (26%) Me, n = 1 (32%). n = 2 (28%) Et; n = 1 (34%). n = 7 (26%) IP~,n = 1 (38%). n = 2 (23%)

(3)

Friedal-Crafts

Alkylations

with Silicon Compounds

155

In the reaction using a I :4 mixture of allyldichlorosilane and benzene derivatives. higher alkylated compounds than trialkylation products were not obtained. This is apparently due to the steric hindrance between substituents on the benzene ring and the incoming allyldichlorosilane. Alternatively, step by step alkylation gives the corresponding products in higher yield than that of the one step reaction. In ;I mixture of dialkylated products. the case of benzene with allyldichlorosilane. W- and p-bis[ ( 1-dichlorosilylmethyl)ethyl Ibenzenes. were obtained in 59% yield from the reaction of monoalkylated product of benzene with another mole of allyldichlorosilane. Purification was also easier. Allylchlorosilancs reacted with naphthalene to give isomeric mixtures of polyalkylated products. However, it was difficult to distill and purify the products t’or characterization from the reaction mixture due to the high boiling points 01 the products and the presence of many isomeric compounds. The alkylation of anthracene with allylchlorosilanes failed due to deactivation by complex formation m,ith anthracene and the self-polymerization of anthracene to solid chat.

Ferrocene behaves in many respects like an aromatic electron-rich organic cornpound which is activated toward electrophilic reactions.5’ In Fricdel-Crafts type acylation of aromatic compounds with acyl halides, ferrocene is 10” times more reactive than benzene and gives yields over 80%.5’ However, ferrocene is different from benzene in respect to reactivity and yields in the Friedel-Crafts alkylation with alkyl halides or olefins. The yields of ferrocene alkylation are often very low. and the separations of the polysubstituted byproducts are tedious.“.” type alkylation offerrocene with allylchloJung rtd. reported the Friedel-Crafts rosilancs.“8 The reaction of ferrocene with allylchlorosilanes in the presence of Lewis acid afforded regiospecific alkylated ferrocenes bearing chlorosilyl groups at the P-carbon to the ferrocene ring (Eq. (4)). To optimize the alkylation conditions. ferrocene was reacted with allyldimethylchlorosilane (2) in the presence of various Lewis acids such as aluminum halides and Group 10 metal chlorides. Saturated hydrocarbons and polychloromethanes such as hexane and methylene chloride or chloroform were used as solvents because of the stability of the compounds in the Lewis acid catalyzed Friedel-Crafts reactions. The results obtained from various reaction conditions are summarized in Table IV. As shown in Table IV, the highest catalytic activity of metal halides used as Lewis acid for the alkylation reaction of ferrocene with 2 was observed in methylene chloride solvent. Among Lewis acids such as aluminum chloride, aluminum bromide, and Group 4 transition metal chlorides (TiCI+ ZrCIa, HfCIJ), catalytic efficiency for the alkylation decreases in the following order: hafnium chloride > zirconium chloride > aluminum chloride > aluminum bromide. Titanium chloride

156

JUNG AND YOO

7’ Lewis acid

-I’]-” A>

R’ = H. Me, Cl R’ = alkyl groups (Me. ‘Bu, “C6H13) n=o. 1.2 m=o. 1.2 fl+m=l or2

showed

no catalytic

Lewis

acids

Lewis

acid.

When

;I catalytic

decreased

orally.

aluminum

chloride

It is well

documented

zation

species

electrophilic

related

to the acidity

ferrocene

undergoes

lylchlorosilanes

decrease

It seems likely alkylation

of Lewis

two competing

and the complexation

that aluminum

chloride

with

chloride

converted

Gen-

acidity

complex

of

is formed.

to ferrocenium

is more

reluctant

to

ferrocenes are not This suggests that

Friedel-Crafts

Lewis

ferrocene.

and the Lewis

The yields of alkylated acids used as catalysts. with

In the stoppcd

and as a result

reactions:

activity

proceeded. eventually

complex

can bc oxidatively

clectrophiles.

substitutions.‘” order

reaction

as a ferrocenc/aluminum

that ferrocene

a strong

was used, the catalytic

transfer

toward

to note that mild chloride,

as the reaction

the nlkylation

a charge

of ferrocene

by most common

undergo

chloride

a deep blue color.

by forming

both the reactivity

It is interesting than aluminum

to green-blue

temperatures,

turning

deactivated

effective

of aluminum

changed

reaction

with the mixture

for the alkylation. are more

amount

and the color

:ase of higher becomes

activity

such as HfClj

acid catalyst,

alkylation

with

which

deactivates

a-

lhe catalyst.“” To find the optimum amount of catalyst for the alkylation, hafnium chloride-catalyzed alkylation was carried out usin g various mol% of the catalyst with respect to allylsilane used. The alkylation rate increased as the concentration of catalyst

increased

from

S to 80 mol%,

but the reaction

was too slow

mol’% catalyst. In these experiments. it was found that hafnium best catalyst for the alkylation of ferrocene with allylchlorosilane. Among methylene chloride. chloroform, carbon tetrachloride. reaction rate was observed in methylene chloride or chloroform

chloride

with

5

was the

and hexane, fast solvents. but slow

Friedal-Crafts

Alkylations

157

with Silicon Compounds

LrNi\ Acitl (Inot’/r )’

Solvent

Te1nl7. TI~W ( Cl (Ill

AICI3 (IO) AIBr; (IO) TiCI, ( IO) ZrcIJ ( IO) Ht’CI, (IO) HKI, (5, HIY‘I, (20) Hfrl, (40) IifCl, (X0) Ht’CI, (IO) HKIJ ( IO) Hf’Ul ( IO)

CHlCl: CH$Y12 (‘t-t~Ct~ CH2CIz (‘H$Iz C’H&I? CHJ(‘Iz C‘HKI, (.H;CI; t~exanr WI, CHCt3

0 0 0 0 0 0 0 0 0 Rtzll~~x II 0

I .5 I.5 I.5 I .s I..5 2 I I 0.75 6 6 3.0

77 71 0 Xl x9 3O’l XI 78 67 40’ 4’ 86

h 7 0 8 x 0 I5 6

h

rates were observed in non-polar solvents such as hexane and carbon tetrachloride. Methylene chloride was found to be the best solvent. The substituent effects on the silicon ofallylsilanes were studied in the presence of hafnium chloride as catalyst. The results obtained from the alkylation with several different allylsilanes arc summarized in Table V. The reactivity of allylchlorosilanes for the alkylation of ferrocene depends on the substituents on the silicon atom. The reactivity increases as the number of alkyd groups on the silicon of allylsilanes increases. Allyl(dialkyl)chlorosilanes having two alkyl groups and one chlorine reacted with ferrocene in the presence of IO molc/rs HfCll under mild reaction conditions (0 C, I .S h) to give alkylated products, (2-silyl- I -methylethyl)ferrocenes, in good yields (89-96’2). but allyl(alkyl)dichlorosilanes required 50 mol% HfClA as a catalyst and reflux ternperatures to give alkylation products. Allyltrialkylsilanes undergo decomposition in the presence of hafnium chloride catalyst and allyltrichlorosilane and allyldichlorosilane showed little reactivity. The reactivity of allylsilanes for the alkylation offerrocene decreased in the following order: allyldialkylchlorosilane >

158

JUNG AND YOO

HfC‘I.,-(‘.\T;\I Y/t:11 AI.KYI ,\ I IO\ 01 FI.I
(‘I

YII I IIj

I)ectrmp”\‘ti”“‘I X9 s 00 0 0I 5 96 0 x 0 -I 0

allyl(alkyl)dichlorosilane >> allyldichloroxilane x allyltrichlorosilane. This reactivity order of allylchlorosilanes for the alkylation of ferrocene is opposite to that of allylchlorosilanes for the alkylation of substituted benzenes. Considering that the alkylations of both substituted benzenes and ferrocene are electrophilic substitution reactions, these results are unexpected and surprising. Although the cause of the reactivity differences in the alkylations of benzene derivatives and ferrocene with allylchlorosilanes is not clear. it is probably related to the complexation of ferrocene with the Lewis acid catalysts.5”

6. Alkylation

with Vinylchlorosilanes

Vinylchlorosilanes react with aromatic compounds in the presence of Lewis acid to give the alkylation products 2-(chlorosilyl)ethylarenes.‘.““’ In the FriedelCrafts alkylation of aromatic compounds, the reactivity of vinylchlorosilanes is slightly lower than that of allylchlorosilanes.“‘~’ ‘-x Friedel-Crafts alkylation ol benzene derivatives with vinylsilanea to give 2-(chlorosilyl)ethylarenes was first reported by the Andrianov group (Eq. (S)).” The reactivity of vinylsilanes in the

Friedal-Crafts alkylation silicon

to aromatic

Alkylations

compounds

159

with Silicon Compounds

varies

g upon

depcndin

the substitucnta

on the

of vinylsilanes.

AI&

reflux, 4 h

(5) X’ = X’ = X” = Cl (679) X’ = Me,

X’ = X3 = Cl (59%)

X’ = X2 = Me. X3 = Cl (25%)

Vinyldialkylsilanes undergo

with benzene

but vinylchlorosilanes reactivities

react

derivatives

with

ofvinylchlorosil:mes

chlorosilane bc described

of benzene

in detail.

chlorobenzenc, lated products

Benzene temperature

Alkylation

with

in the following

excess

for 4 h to give

with

3 in the presence

peralkylated

(4b).

respect

When

(4~).

(4d),and

around

increased.

the monoa

h-fold

tris

bis[3-(methyldichlur(~silyl)ethyl]-

distributions

distributions

one equivalent

to 3, the yields

at

hexakis[?-(methyIdichloro-

products:

were plotted

against

II-wle

ratios

I.

the same,

SX%)

at room

2-(mcthyldichloro-

in Fig. I, product

less than 5% yield.

chloride

tetrakis[2-(methyldichlol-osilyl)ethyl]benzene

(4e) (Eq. (6)). The product

As shown

alky-

pentakis[

12-(n~cthyldichlorosi1yl)ethyl]benzene

3 to benzene.

such i15 toluene.

the corresponding

of aluminum

product,77

silyl)ethyl]benzenc

in Fig.

(3) will

I”

(4a) and other alkylated

benzene

vinyl(methyl)di-

benr.enes

(‘ for 3 h afforded

silyl)ethyl]benzcne

ol‘3/ben~cne

order:

n~ethy1(cinyl)dichlorosilane

of monosubstituted

at 75-80

in SO-K%% yields.

reacted

do not

> vinyl(dimethyl)chlorosilnnc.

derivatives

and biphenyl

atoms

in the presence ofaluminum chloride” products. The to give the alkylation

benzene decrease

> vinyltrichlorosilane

The alkylation

havin, 0 no chlorine

and vinyltrimethylsil~~~nc

alkylation

of monoalkylated

SO and 30%. and

while excess

dialkylation

depending excess

and dialkylated

respectively.

LIMOS

rapidly,

benzencs

decreased becoming

of 3 to benzene.

The

the mole ratio 01‘

oi benzene

As the proportion

products

4a increased or more

varied

or a two-fold

and

was

about

of 3 to benzene were

the major yield

used with

remained

formed

product

in (56

01‘ 4b increuscd

to

26%’ at the maximum and then decreased smoothly to I X%1. Products 4c and 4d, however, were produced in yields near IO% regardless of the mole ratios used 01‘ 3lbenzene. To optimize out

using

a

the reaction

time for the synthesis

I :6 mole ratio ofbenzene

ol’4a,

the alkylation

to 3 at room temperature.

Product

was

carried

distributions

160

JUNG AND YOO

AICI,

Cl i ,Me SI ‘cl

z

mono-alylated

3

product

3IAICI 3

n = 3 (4d) n = 2 (4e)

n = 5 (4b) n = 4 (4c)

(6)

BIAICI,

he 4a

were determined at various time intervals. Product distributions are plotted against reaction time in Fig. 2. As shown in Fig. 2. monoalkylated compound W;IS the major product at the intial stage of alkylation, but decreased drastically and almost disappeared after 4 h. However, 4a increased gradually and became the major product in a 2-h reaction

Friedal-Crafts

Alkylations

161

with Silicon Compound?.

-m-4a -.4b -A4c --r--d -*4e

mono

.Yrn

/ ??!!5s!-;

0

I 20

I 40

I 60

I 80

; I 100

I 120

I 140

I 160

I ' I 180 200

I 220

t 240

time. As similarly observed in Fig. I, compounds 4c and 4d were obtained in approximately 10% yield throughout the rest of the reaction time. This indicates that they were being produced from monoalkylated and dialkylated products at almost the slune rate at which they were consumed to give higher alkylation products. Therefore 4a can be produced efficiently by using a e-fold excess of 3 to benzene with 3 2-h reaction time.

In the peralkylation of alkylbenzenes in the presence of aluminum chloride catalyst.‘” both polyalkylation and transalkylation reactions have been reported as competing reactions. The yields of peralkylation products decrease as the chain length of the alkyl substituents on the benzene ring increases. probably due to easier dealkylation under the reaction conditions. Toluene reacted with 5 mol of 3 in the presence of aluminum chloride at room temperature for 2 h to give pentakis[ 2-(methyldichlorosilyl)ethyl ]toluene in 6 I % yield and less alkylated products: tctrakis[2-(methyldichlorosiIyl)ethyl]toluene (12%). tris[2-(methyldichlorosilyl)ethyl]toluene (60/c), bis[2-(n~ethyldichlorosilyI)ethyl]toluene (2%), and [2-(methyldichlorosilyl)ethyl]toluenc (2%) based on toluene used. The peralkylation reactions ofalkylbenzenes having longer alkyl groups such as ethyl, Ii-propyl. and rl-butyl with 3 gave the corresponding peralkylated products in low yields (about 25%) along with the transalkylation products (Eq. (7)). The results from the reaction ofalkylbenzenes with 3 are summarized in Table VI. The reaction ofethylbenzene with 5 mol of3 under the same reaction conditions for the alkylation of toluene with 3, gave pentakis(2-(n~ethyldichlorosilyl)ethyl](25%). tetrakis[2-(methyldichlorosilyl)ethyl]-(C)C/c), trisl2-(methyldichlorosilyl)-

162

JUNG AND YOO

m=l-6.n=0-3.m+n<6 m + n = 6: R = Et, n-Pr. n-Bu (8 22%)

3

(7)

R = Me (6196) R = Et, n-Pr. n-Bu (2527”,)

ethyl]-(3%

), and bisl?-(methyIdicl~lorosilyl)ethyl

many

transalkylated

alkyl

substituted

3 in comparison Anschutz

first

products benzenes with

f’OI.YAl

as shown in Tahlc

exhibited

toluenc.

reported

~ethylben~cne

different

products

the dispropol-tionation

2 0

I’S 01

It is of interest

behavior

Transalkylated

K\I I.,\ I‘ION “11Oi)il(

VI.

( I %) as well

expected

of alkylbenzenes

.bti.kYl

2

6

17

I

-I’)

0

i

x

IO

I?

7

IO

II

13

IHI N/t:hh\

that Ionget

in the peralkylation were

as

with because

in the presence

L\ I I tl 3

Tell-nk~\(\~l)dietli~Ihen~elle (II) T~is(~il)diethylh~tl/ent (I I) Uis(sil)dictll\ilhcl~~~lle (2) Hcxnkl~(\il)herl/ell~ ~tracr) Pentahi~(\il)hen/ene (XJ ~l’et~akis(\il)hen/ctlr (7) TI-is(sil)hcn/ene (5) Bi\(Gl)bendcnc (trncc) Tetrnki\(sil)di-lr-propylhen/,ene (‘1) Bis(vil)henLcnc (?-I tSil)henrene (2) Tetl-aki~(sil)di-rr-butylhen~ene (H) Bi\(\il)hen/cnc (2) (Sil)benxnr: (I 1

Friedal-Crafts

of Lewis

acid

chloride ane

as early

at rcflux.

Kennel-

and

it

When

evidence

be concluded

signiticantly

bcn7ene

were

and intra-trunsalkylation

of ethylbenand dicrhyl-

yield

in comparison

and

the dispro-

ofethylbcnzene, with

that the transalkylation lower

Baddeley

from

that the inlcr-

by the polyalkylation

the

of ben-

ethylbenzene

In 1935. obtained

aluminum

to the mixture

benane,

also indicates

with

mixture

a

in the presence of aluminum chloride and I ..i.S-tris(,l-propyl)bcnzene.‘.“’

products

This

into

Similarly,

that the products

zcnc and alkylated followed

was heated

of HI- and /I-diethylbenzene.

/Ais(n-propyl)benzene,

may

toluene

was converted

the UT- and/l-isomers.

ofp-di(/7-propyl)benzene

I!-propylbcnzene, Thus.

mix(ure

a

convincing

163

with Silicon Compounds

that toluene

said to be mainly

presented

portionation

as in 1886.“”

it was found

and xylenes.

gave benzene

Alkylations

with

(15%) those

of

3, lcads

benLcne, to the many

of ethylbenzcne

byproducts.

was responsible

for

pentakis[‘-(methyldicl~lorosilyl)ethyll-

obtained

from

the alkylation

of benzene“

OI

tolLlellc.

Peralkylation

of/l-propylbenzcne

and /l-butylbenzcne

showed

similar

results

to

those of ethylbenzene.

o-. H-. or p-Xylene alkylatcd

xylenes

reacts

consisting

with

4 mol of 3 to afford

~ctrakis[(methyldichlorosilyl)ethyll-,lr-xylene ethyl I-I>-xylene, indicate reaction xylenc

and

isomeric

that reorientation times was

and

favored

mixtures

of perOI

and tetrakis[(n~ethyldichlorosilyl)-

transalkylation

occurred

higher due

isomeric

of tetrakis[(methyldichlorosilyl)ethyl]-o-xylene

during

tcmperaturcs. to less steric

products the alkylation

(Eq.

(8)).

These

results

With

Iongel

of xylcnes.

tetrakis[(methyldichlorosi1yl)ethyl]-/Thindrance

between

the substituents

on

benzene.

rcyh I’-1 + ,+&Me 3 - ,&dMe)m r:l-: 61 o-. m-, or p-Xylene

m=l-4

3

(25

It has been reorientation

demonstrated without

by several

any observable

investigators

transalkylation.

64%)

that methylarenes Baddeley

undergo

rt 01. reported

that

164

JUNG AND YOO

a mixture

01‘p-xylene

no change

gave

reorientation ratio

and aluminum

occurred

to product

of ca. X:7:27

products.“‘.“’

= AZ//>)

These

reports

p-xylene

was easily

products,

monoalkylated

isomers

products

Peralkylation

of mesitylene

with

It was f’ound

by carrying

for I? h.

In

out

this reaction.

ethyllmesitylenc,

was

from

to the

peralkylated obtained

THF.

The

(in ;I

1.55

less alkylated

The yields

reoriented

in hexane

along

in Table products

VII.

but

isomerizution

no

at

&an\-

of 2.4.6.tri\-

could

or 1.5.Cisomers solution

with

of peralkylated

I-oom

he

temperature

. 1.4.6trisl2-(methyldichlorosilyl)-

product

in 38%

isomers

results.

arc summarized

that the undesirable

the reaction

I h

of’ transalkylation

were also formed

group.

only

gac’c

xylene

formation

compounds. isomers

3

for

bromide.

tetrakis[(methyldichlorosilyl)ethyl~-

of the methyl

(n~ethyldichlorosilylethyl)n~esitylene avoided

01‘ the three

by recrystalli,ation

including

temperature

oP hydrogen

well to the above

symmetry.

due to reorientation

products.

mixture

no appreciable

to trialkylated

and less alkylated alkylated

a

correspond

purified

kept at room

but in the presence

with

Because of its high structural

many

bromide

in the hydrocarbon.

yield

alon g with

~nono-

and dialkylatcd

mesitylene without any reoriented products in 7 and 37% yields, respectively. The Fricdel-Craf’ts type polyalkylation ofalkyl-substituted henzenes with 3 becomes easier and faster as the number ot‘clectron-donating methyl groups on the phenyl

group

in the fashion Lanes to fhrm

increases.

This

is consistent

with

the fact that the alkylation

occurs

of elcctrophilic substitution. The tendency of starting mcthylbenreoriented products also increases in the wmc order ti-om toluene to

mesitylenc. The alkylation of bcnzenes having electron withdrawing groups, such as chlorobcn/.ene and anisole, with 3 gave only mononlkylated. dialkylated. and trialkylated compounds.‘.”

but no peralkylated

products

were obtained

even upon

heating

of

Friedal-Crafts the reaction

mixtures

Alkylations

for long periods.

of the electron-withdrawing catalyst

with Silicon Compounds

This

tnight

substituents

and the lone pair electrons

and

165

be due to the deactivation

the cotnplexntion

effect

betw,een

AICI3

on the substituents.

IV FRIEDEL-CRAFTS ALKYLATIONS OF ARENES WITH (CHLOROALKYL)SILANES The Friedel-Crafts presence lations

alkylation

of Lewis with

acid

of aromatic

is well

defined

chlot-osilanesX.‘J-‘“.‘X~“’

been

relatively

unexplored

rials.

(Polychlorinated

due

compounds

in organic

containing to the lack

methyl)chlorosilanes

in the photochlorination

process “-w

I -yl)mcthyl

l’rom 5 by Moberg also studied

Isilane,

in 1985.“”

the synthesis

rosilancs

[ (CI,,Hj-,,C)SiXj.

starting chlorinated

reactions

of aromatic alkyl

will be described

been

in the alky-

groups

have

starting

mate-

as byproducts for the prepara-

In

were studied.

as byproducts

hydrocarbons

with

in the photochlorination

of benzene

in terms ofsubstitucnt

to re-form the (poly01‘ (chlori-

‘-’ and ’ their alkylation

reactions

will dcscribc

ethyl.

with

a variety

(chlorinated

such as methyl,

of

methyl)chlo-

of byproducts

series of these works. This section

rt trl.

starting

by the chlorination””

of(polychlorinatecl

alkylarion

starting

Jung

cotnpounds”7.6”

the dechlorination ;I

IH-

was prepared by Du Pont.

can be prepared

applications

n = 2, 31 formed

groups

of the (chlorinated

A. Alkylation

produced

was synthesized”J.“‘.““.7’

derivatives

ing short chain el‘fcct

which

tncthyl)chlorosilanes.

with benzene

have

organoailicon

and the Fricdel-Crafts

nated alkyl)chlorosilanes

available

and was commercialized

they studied

materials”’

alkyl

of readily

as ;I good fungicide,

of new bioactive

To find useful

of tncthylchlorosilanes.

chlorinared

halides However,

(5). Bis(4fluorophenyl)methyl[(

known

l‘rom (chloromethyl)trichlorosilane tnethyltrichlorosilane.

alkyl

of ditnethyldichlorosilane

tion of (chlorotnethyl)tnethyldichlot-osilane I .3,4triazol-

with

chemistry.’

the Friedel-Crafts

alkyl)chlorosilancs propyl

groupc.

efi’cct on the silicon

These

and alky-chain

containreactions length

alkyl)silancs.

with (~l~-Chloroalkyl)silanes

(Chloroalkyl)silanes

have been reported

to react

with

aromatic

compounds

in

the presence of aluminum chloride catalyst to give the corresponding alkylation pr-oduc~s (Q, (g)).x.‘~--‘(‘.‘x~20 However. the details of the alkylation were not reported. Thus, Jung et rrl. undertook a systematic investigation of the alkylation 01 silanes

containing

2, 31 lo benzene

a terminal in the presence

chlorinated

alkyl

of aluminulii

group chloride

ICI-(CHZ),,,SiX3, catalyst.

n =

In this work.

I. the

166

JUNG AND YOO X’ X’-~I-(CH~),CI i3

alkylation

reactivity

stitucnts

on the silicon

bond. The results reaction

at lower

tically to ethyl

as the spacer

in Table

between

C-Cl

length

and to propylene, of the neighboring

on

between

C-Cl

that

of (chloromethyl)silancs.

temperatures

as the number

and the silicon

increased

of chlorine

increases

increases

bond and

111 the case of substituent

the reactions groups

on

occurred the Glicon

dras-

from methylene

of C-Cl

electron-withdrawing

trichlorosilyl-group.

on the silicon

of (OF occurred

and to (y-chloropropyl)silane.

the activation the

and sub-

reactions

rate of(c~xhloroulkyI)silanes

both

at various

the reactivity

The alkylation

of(o-chloroalkyl)silanes

reflecting

depends

and C-Cl

and the silicon

affects

to (jf-chloroethyl)silane

show that the alkylation

on the sub-

the silicon

VIII.

of benzene. length

to depend

betwecn

with (w-chloroalkyl)silanes

the spacer length

in the alkylation

as the alkyl-chain

chloroalkyl)silanes

length

atom of (c+chloroalkyl)silanes

(chloromethyl)silane

These results

effects

for the alkylation

in Table VIII,

temperature

was found

and the spacer

are summarized

on the silicon

chloroalkyl)silanes from

atom

obtained

temperatures

As shown stituents

of (w-chloroalkyl)silancs

at higher

increased

of (asteric cff’ects reaction fl-om

Friedal-Crafts

Alkylations

(chloromethyl)trimethylsilane

to (chloromethyl)methyldichlorosilane

romethyl)trichlorosilane. benzene

under

perature

of 200

49%

In particular,

drastic

conditions

C in a sealed

benzene lower

were boiling

obtained

to afford stainless

tube.

;IS observed tween indicates

with

as toluene.

xylene,

reaction

with with

ability

on the silicon.

(c+chloroalkyl)silanes

group

” Other with

naphthalene in the presence in Table ,x~x.lJ’l”.lx.“’ To prepare polyalkylation chlorosilane

multifunctionalir.ed of benzene. were

(Z-chloroethyl)silane of aluminum benzene

chloride

with

The

compounds

obtained

symmetric

orgnnosilicon

reacted

with

benzene.

catalyst

at a reaction

of chloro-

the reaction dericati\,es

of and

arc summ;u-izcd

compounds

by the

of

benzene

with

were c:u-ried out in the presence temperature

with excess (2.chloroethyl)trichlorosilanes

hexakis(Z-(trichlorosilyl)cthyl)benzene

Il-om

and (.?-chloropropyl)tri-

Polyalkylations

and (3-chloropropyl)silane

bcThis

since the elcctronnumber

as catalyst

(3-chloroethyl)trichlorosilane

rate of

spacers

on the silicon.

such as benzene

compounds

one chlocompound\

alkylation longer

effects

increasing

products

of aluminum

boiling

substituents

by inductive

alkylntion

aromatic

lower having

chlorine

were

containing

with

trimethylchlorosilane.

increases

but

and trimethylchlorosilanc

along

bond is deactivated

(trichloroailyl-

(chloromethyl)trimethylsilane.

(chloromethyl)silancs

products,

and fewer

of silyl

to give

of‘ ((trimethylsilyl)methyl)-

(tic,-chloroalkyl)trichlorosilanes

and the silicon

that the C-Cl

withdrawing groups

in the alkylation

in the alkylation

tcnonly

consumed

such

The

with

product: a reaction :I X-h reaction period.

products

observed

was faster with C-Cl

After

was

No alkylated

also gave alkylation

reacted

the alkylated

products

instead.

rine on silicon bcnrene

in 3 1% yield.

and to (chlo-

(chloromethyl)trichlorosilane

of the (chloromethyl)trichlorosilane

methyl)benzene

167

with Silicon Compounds

in good

of 80 C. The reaction

afforded yield

pcralkylated

ot

product.

(7(W).”

Cl \ Cl + others

(IO)

68

JUNG AND YOO

AL.KYI.,I

I ION COWI

((‘III.OIIO;\I.KYI

,,I

x

0 (I

)SII.,INb.S

I IONS OI. BENILNI.

L)txi\u

(X’X’X’S,(CH2),,,(‘HXCI)

K”

C‘JI

H

H

AI(‘I;

H

(‘I

AI(‘I;

I IL’t:s ( K-PII) ,ANI)

WI tl PKOI)I (“I YII 1.1)~

I Ii-

Kel x. 17. 20 8

0

H

hlc

Al(‘l;

0

Me

H

AI(‘I:

I2 s

0

I:1

H

,\I

IS

0

SKY,

II

.\I(‘1 ,

12

I

II

I

II

II

?\i(‘l:

s. I’.

I

tl

H

,\I

Ii

I

II

Cl

:\l(‘l,

I2

I

II

hlc

;Zi(‘l:

.\I Ii

I2 x.

(‘I 1

I

II

I’ll

,\I

15

(‘I 3

I

II

11:1pl1

,\l(‘l,

15. IS

(‘I 3

I

ti

01’11

i\lC‘l i

Ii

(‘I :

I

hlc

II

/\lC‘l:

IS

( II (‘I;

I

hlc

IIC

i\lCl

IX

I

MC

I’ll

41

IX

(‘I:

I

MC

I’ll

:\Ic‘I?

IX

Cl:

I

MC

01’11

-\I(‘1 <

IX

(‘I;

1

H

H

,\I(‘1

IX

(‘I;

1

H

( I

!\Ic‘I,

IS

(‘Ii

1

tl

\lC

Al

IX

(‘I:

?

II

I’ll

:\l(‘l:

IX

(‘I 1

2

II

01’11

.\I(‘1 >

(‘13

1

H

11‘1pll

.\I(

h,lC.C‘I~

0

H

II

,Il(‘l,

h,lC.(‘lJ

0

II

(‘I

-\l(‘l:

I6

Xle.(‘lJ

0

H

hlc

,\l(‘l,

Ih

hlC.C‘l?

I

hlc

II

,\I

IX

IlC.(‘l~

I

hlc

(‘I

.\I (‘I;

IS

hlC.(‘i~

I

hlc

hle

IX

hlc.(‘ll

I

hlc

I’ll

IS

hk.(‘l-

I

\I?

01’11

IS

hlc.(‘l1 MC.(‘lJ

klc Vie

Ililpll tl

IS IS

hlC.(‘l~

I 1 _7

\Ic

(‘I

*\I

IX

‘1IC.CI~

1

hle

hlc

,\I(‘1 j

IX

\IC.(‘i>

7

hlc

Ililph

.\l(‘l,

IS

1:1.(‘1>

0

hlc

II

AIC‘I?

Ih

t%( I;

0

H

C‘I

?\lC’lI

I (1

f:l.(‘l,

0

II

hle

.\lc‘l;

Ih

t.l.(‘l,

H tl

H

:\l(‘l,

12. Ih

t.l.(‘l.

I I

(‘I

.\I( I,

t.1.(‘1:

I

II

hlc

,\i(‘l:

I6 I6

IX IS

I?

MCI;

s

8. If>. lli

Friedal-Crafts The

reaction

peralkylated

of benzene

product,

Alkylations

with

excess

with Silicon Compounds

169

(3-chloropropyl)trichlorosilane

hexakis(3-(trichlorosilyl)propyl)benzene.

afforded in moderate

yield

(53% ).74

+C’ C’\ ,/,&

RT

Cl

_

(kJ-‘-$;,

+ others

AIC13

(I 1)

80°C/AIC13

B. Alkylation

with (Dichloroalkyl)silanes

The alkylation the presence products.

of benzene

of aluminum

with

(w,o-dichloroalkyl)silanes

chloride

catalyst.

(w.w-diphenylalkyl)chlorosilanes

The results

obtained

from

The

alkylation

in fair to good

the alkylation

reaction

between

the C-Cl

and silicon

gave yields

in

diphenylnted

(Eq. I 12)).

of (to,w-dichloroalkyl)silanes

with excess benzene are summarized in Table X. As observed in the alkylation with (w-chloroalkyl)silanes,‘4 length

was also studied

and the substituents

both on the silicon

the spacer atom

of

170

JUNG AND YOO TABLE Al.tir,

I.XfION

CONIN

x

I IOYS Ol- i~I~N7I:hl.

,\NI)

(w.to-dichloroalkyl)chlorosilanes for the alkylation alkylation

of benzene

temperature

with

the spacer

as

(dichloromethyl)silane

(‘I

-I’ll I I)\

in the presence

occurred from

dichlorosilanes,

chloride

(o,,cr,-dichloroalkyI)trichlorosilanes length

between

the C-Cl

and silicon

while

at X0 C. As the number were obtained

The

at IOWCI

increased

alkylation

t’rom

proceeded

the alkylation

ot’chlorine

(dichloron~cthyl)trichlorosilancs

the products

catalyst.

occurred

The

with (2.2-dichlorocthyl)silanc.

romethyl)silanc

of(c,~.w-dichloroalkyl)sil~~ncs

of aluminum

to (2,2-dichloroethyl)silane.

room temperature icon decreased

f’ROl,l

affect the reactivity

of benzene

Vv I l’il

ICl2XSi(Cti~),,,(‘H~l~)

I~~~.~~~-~~l~‘lil.oKoAI.KYI.)sll,,\Nl~~

at

with (dichlo-

substituents

on the sil-

to (dichloromethyl)methyl-

in good

yield

after

shorter

a

reaction

period. In the alkylation aluminum spacer

of benzene

chloride

length

catalyst.

between

with (dichloroalkyl)chlorosilanes

the reactivity

the C-Cl

and silicon

on the silicon

of (dichloroalkyl)chlorosilanes

the alkylation

with

the corresponding

diphenylated

in the presence products

chloride substituted summarized

with

catalyst

other

afforded

phenyl)alkylsilanes in Table

in moderate benzenes

(dichloroalkyl)silancs isomeric

mixtures

in moderate

increases

the number

as

as

The alkylation

data are summarized in Table XI. The alkylation of halogen-substituted chlorobenzenes

and

decreases

(w-chloroalkyl)silanes.

with other (dichloroalkyl)chlorosilanes

in the presence

of(dichloroalkyl)silanes

of

as the

of chloro-groups

similarly

observed

of benzene

of aluminum yields.“.”

in

derivatives chloride

Those

such as fluorobenzene

gave

synthetic and di-

in the presence

of aluminum

of the corresponding

(dihalogen-

yields

(Eq.

(I 3)). These

results

arc

XII.

X’ F’

+ ClaH2,.,C,-Si-R Cl

-

AK&

F’

(X’X2C6H4)2H2,~,C,-s~-R Cl

(13)

Friedal-Crafts

TARLI: ALK~LATION

CONIXI

IO%

0 0 I I I 0 0 0 0 0 0

H H H H II Me Me Mc Mu hle Me

In extension nated were on

such

alkylated the

with

chloride ring

(R-t%)

.,\hl)

PKOI)II(‘T

ho

IO

64

so I5 26 3 3x 40 s 0 32 4

reactions

Although the

and

TAl3LE

I2 I7 I7 17 I7 I7 I7 17 17 17 17

II ‘I -II ~ ~ ~

pulychlori-

in the presence chlorine

substitution

reaction,

the

I)EKIV,ZI’IVFS (X’X’-ChH4)

(C12RSi(C,,H2,,~

,CIJ)

j~~~~ Ylf;Ll)S

OF PKOIN(‘II ((X1X~C~,H,)2H2,,~,C,,SiRCI)

Me

I

I,I-

Mc

I

I,I-

H Cl

F I-Cl

Reflux I.50

Cl Cl (‘I Cl Cl

2 7 2 3 3

I .2I .21.2. 2.3. 2.3.

Cl Cl Cl I-1 H

i-Cl J-Cl 4-C-I H F

I?0 I20 x0 70 70

of alu-

substituents

XII

I’IONS OF B~N%I!I\;F

~Dl~~Hl.ORO~LKYl.)SlLi\NtS

YIELfX

I ,2,3,4-tetrachlorobenzene

the electron-withdrawing

electrophilic

~oix CONIII

11 ITI I

to polychlorobenzenes,

( I ,2-dichloroethyl)trichlorosilanes

deactivated

WITH

IVIS

-

as I .2.4-trichlorobenzene

catalyst.

AI.KYL,A’I

DEKIV,\I

AICI; AICI; AICI; AICI; .AICI; AICI: AU; AICI: AICI; AICI1 AI<‘13

of the alkylation

benzenea

minum

H Cl II Cl hlc H Cl Mc H Cl Mc

XI

OF Bf:vzbw

(CI~X’S,(CH2),,,CX~Cl~)

(Dl~flLO~O~~l.KYl~)Slf,~N~S

Cl Cl (‘1 Cl Cl MC MC MC Mc hlc Me

171

Alkylations with Silicon Compounds

2.0

6.5

7.0 0,s 0.5 I .o 0. I 0.2

47 39 33 59 76 11

alkylation

172

JUNG AND YOO

proceeded I‘or 0.3 h at I20 C to give unusual 5-membered ring products.“’ In the cast of alkylation of 1.2.4.trichlorobenzene, dialkylation products, [3.?bis(trchloro phcnyl)ethyl]trichlorosilanes. and cyclic products, I-silylmethyl-2-silyl-3. trichlorophenyl-4,5(6).7-trichloroindanes. wtx obtained in 57 and 6% yields (Eq. ( Id)), respectively.“’ The alkylation of I .3.3,~-tctrachlorobenzenc gave cyclic products, I -silylrnethyl-.3-(~..3,4.5-tet~-achlorop~~e~~yI)-4,5,6,7-tctrachlor~~i~~d~~n~ and I -silylmethyl-3-(2,3,4.S-tetrachlor~~phenyl)-3.5.~.7-tctrachloroindane, in 5X and 5% yields. respectively (Eq. ( IS)).“’ Cl

( 13)

\, :II(:: Cl

Cl Cl

.CI

S

Cl

‘Cl

/

F’ ” yl-cl

’

Cl Cl

C’

Cl

/

\

(IS)

Cl

’

(Dichloroalkyl)chlorosilanes undergo the Friedel-Crafts alkylation type reaction with biphenyl in the presence of aluminum chloride catalyst to afford 9-((chlorosilyl)alkyl)tluorenes through two step reactions (Eq. (I 6)). The results obtained from the alkylation of biphenyl and the cyclization reaction to Smembered-ring product are summarized in Table XIII.

F’

R = H. Me

Friedal-Crafts

Alkylations TABII

XIII

AI KYI.,VI ION CONI)ITIONX OI; BIPHIW L M I TH ( DKIILORO~LKYI (CIIXSi(C,,,HI,,,~lCI2)) hNI1 YllLI~S ()I: ~l~Ol)M‘TS ((CI~H~~K)-(CHZ),,S~)(CI~)

Cl Me MC hlc Me

2 I 2 ? -I

C. Alkylation When

chloride

as the major

products

( 17)). Excess

due to polyalkylation

I 0 I 2 2

-34 59 IX 17 34

with

was used to avoid

the reactivity

were

in the aluminum with methyl

the electron-withdrawing silanes, were presumably

benzene

in the presence

(diphenylmethyl)silanes

of one phenyl

on silicon.

methyldichlorosilanes

excess

(triphenylmethyl)silancs

were ;1s minor

the production

obprod-

of polymeric

group.

ofbenzene

with (trichloromethyl)silanes

XIV.

in Table XIV,

in the alkylations electron-donating

along

from the alkylation

in Table

the substituent

chlorosilanes

with

temperature,

benzene

The results obtained are summarized

reacted

at reflux

materials

As shown

II H H H Me

)~II.AWS

with (Trichloromethyl)silanes

ucts (Eq.

ing upon

3 1.5 0.2 2.0 I .O

I30 I20 I70 I-IO IO0

(trichloromethyl)silanes

of aluminum tained

I .2I.II .7?.i25

173

with Silicon Compounds

of(trichloromethyl)silanes

The reactivity

slightly

higher

chloride-catalyzed

(w-chloroalkyl)silanes group on the silicon chlorine. derived

than

and yields those

varied

depend-

of(trichloromethyl)-

of (trichloromethyl)tri-

alkylation

as similarly

observed

and (dichloroalkyl)silanes. facilitates the alkylation more

The than

The minor products, (diphenylmethyl)chlorofrom the decomposition of (triphenylmethyl)-

chlorosilanes. To examine

the decomposition

methyl)chlorosilanes

during

of (triphenylmethyl)chlorosilanes the alkylations

of benzene

with

to (diphenyl(trichloromcthyl)-

174

JUNG

AND YOO

TABLE ALKYI

~vr10\

XIV

COWI-IXIN~”

POK HI.N/.~NI.

MI I II

~TI~I(‘II1.0I~0C11:IIIYI )sIl..\\li\ (C’I~XSiCCI;) 4uI) YII:l.rx 01 I’l~ol~lJc~lS (CI?XSiCH2 ,,(Ph),,)

Cl (‘I Me Ml2

60 0-l 72 OS

I 2 0.5 I

7 i

7

IS 2.i

18

chlorosilanes in detail. methyl(triphenylmethyI)dichloroailane was stirred under the same alkylation conditions but without starting material. As expected, methyl(diphenylmethyl)dichlorosilane was obtained (Eq. (I 8)).

(18)

The results obtained from the decomposition reaction 01‘ (triphenylmcthyl)methyldichlorosilane to (diphenylmethyl)methyldichlorosilane in benzene solvent in the presence of aluminum chloride are summarized in Table XV.

TABLE IX.(‘Ohll’OSI

xv

I ION 01. (‘lIIPH1:h~

MF7HYI.)RIF~HyL.I~ICIiI.Ol~OSII

I_-

.\\I.

(1) TO

I~IPHI:NYI.~~~~~HyI.)~lE7HYI.I~I(‘HI.OKOSII.RI\I

(II) IN I tit Ptks~~ruc?: ()I- Alt.1;

rl

?

80 80

I 7

IO0 x5 77

IO 70

0 0.12 0.3x

Friedal-Crafts

As shown silane

in Table

at room

temperature,

1 and 2 h reaction

periods.

reaction

as observed

The results

conditions

the

of benzene

phcnylmethyl)dichlorosilane solvent

phenyl

on the methyl

groups

and toluene

occurred

group

silanes

interacts

as catalyst with

R

reaction

reaction

chloride

the exchange

was carried

reaction

between

aluminum

7’

X-Si-(CH2),-F Cl

r-eoctiorls

The mechanism

with chloroalkylsilanes in Scheme chloride

I’ X’

and (di-

I ).75.7h

~rlti ~.~hcrngr

is outlined

of

of methyl(di-

of (diphenylmethyl)(methyl)dichlorosilane (Scheme

as an example,

in

to triphenylmethane.7’.7”

to give [phenyl(tolyl)methyl](methyl)dichlorosilane

a. M~c~h~tr~isrn fi)r- dk~lutiotl chloride

occurs

the decomposition

of aluminum

at X0 C. In this reaction.

of after

(trichloromethyl)chlorosilanes

the decomposition

tolyln~ethyl)(methyl)dichlorosilane

of benzene,

from

in the presence

out in toluenc

temperature

that the decomposition with

of tetraphcnylmethane

production

methyl(triphenylmethyl)dichlorosilane,

minum

at the reflux

in 10 and 20% yields

indicate

of benzene

in the decomposition

To confirm

175

of(triphenylmethyl)methyldichlorobut occurred

to give (diphenyh~~ethyl)methyldichlorosilane

the alkylation

alkylation

with Silicon Compounds

XV, the decomposition

did not occur

benzene

Alkylations

2. The C-Cl

catalyst

to give

in the presence

for the ofalu-

bond ofchloroalkyl3 polar

‘+C-Cl”

176

JUNG AND YOO

F’ ? X-?I-(CH,),? Cl X2

I<

(“+C-CI---AI”PC13) diate

intermediate

electrophilically

attacks

intermediate

which

gives

tetrachloride

anion.

Finally

aluminum

chloride

in the catalytic in the presence aluminum

alkylated

of aluminum

chloride

present

in the reactants.

initiates

chloride

and aluminum

chloride

mechanism

cation

a small

interme-

complex chloride

affords

is recycled

to give

The proton

ion which is deprotonated methyl)silane. This proton for the production

alkylation

the presence

of aluminum

reaction chloride

cation

(“+C-Cl--AI”~-Cl;)

re-

a ben-

of benzene.

71.1X

(R’ AICll

)

to give an alky-

to generate a proton (H+AICIJ-) is recycled in the catalytic cycle ol‘

of 9-((chlorosilyl)alkyl)fluorencs from with (I .2-dichloroethyl)silane

as catalyst

the

from hydrogen

intermediate

with toluene

In

inevitably

ring to generate

of biphenyl

beginning stage of the reaction, one of two C-Cl (CICH?-CICH-SIX?) interacts wjith aluminum “tC--CI”P

resulting

to the @so-carbon

interacts

toluenc 3.

chloride.

with moisture

with the benzene a alkyl

with

in Scheme

of hydrogen

chloride

protonation

intermediate

is outlined amount

aluminum

interacts

through

Friedel-Crafts

diate 1 (a polar

This

of (diphenylmethyl)silane

the reaction.”

is dealkylated

The alkyl

lated toluenonium and give (tolylated alkylation. The

ofanhydrous

ion intermediate

intermediate

tetrachloride

gas. This aluminum

as catalyst

reactions,

from the reaction

and benzene.

.“.”

of alkylation.

sulting

This

aluminum

chloride

for the transalkylation

chloride-catalyzed

zenonium

C ’AICL-

rin g to generate a benzenonium ion through deprotonation by aluminum

benzene

the hydrogen

and hydrogen

cycle

The mechanism

or a carbocation the benzene

is outlined

in Scheme

the in

4. At the

of( I .2-dichloroethyl)silane chloride catalyst to give intcrmeor a carbocation C’AIC14~~ ).77.7s bonds

Friedal-Crafts

This intermediate

I electrophilically

a 2-phenylbenLenonium tetrachloride silyl-

anion

aluminum

I -chloroethyl)biphenyl

intermediate

III which

intermediate

IV through

tramolecular

Friedel-Crafts

intermediate

V which

tetrachloride gas. This

aluminum

again

with

to afford

complex.

chloride

the alkylation

of aluminum

chloride

alkylations

catalyst

the C-Cl

to aluminum

ofbenzene and silicon

bond

chloride

stable

ben7ylic IV

the other

chloride

carbocation

undergoes

phenyl

ring

of aromatic

compounds by two

and the electronic

aluminum chloride

of alkylation. with (chlorinated

with (w-chloroalkyl)silanes affected

an into give

and a hydro-

and hydrogen cycle

of 2-(2-

to generate

step, the hydrogen

in the catalytic

was generally

tetrachloride

the C-Cl

aluminum

I-

by aluminum

C)-(silylmethyl)fluorene

In the final

is recycled

2-(2-silyl-

aluminum

Then.

Intermediate with

to generate

gives

deprotonation

the more

cycloalkylation

the Friedel-Crafts

between

catalyst.

to give

decomposes

alkyl)silancs, length

through

a I .2-hydrogen-shift.

deprotonates

of biphenyl

intermediate

of hydrogen

chloride

rearranges

tetrachloride complex

Among

chloride

interacts

the 2-carbon

II. This

and dehydrochlorination

to generate

gen aluminum

attacks

and hydrogen

177

with Silicon Compounds

ion intermediate

chloroethyl)biphenyl complex

Alkylations

in the presence factors:

nature

the spacer

of substituenta

on the silicon atom of (w-chloroalkyl)silanes. As the spacer length between the C-Cl and silicon increases from (chloromethyl)silane to (P-chloroethyl)silane to (y-chloropropyl)silane, the reactivity of the silanes increases. As the nunher ofchloro-groups

on the silicon

to (chloromethyl)methyldichlorosilanes

decreases to

from

(chloromethyl)trichlorosilancs

(chloromethyl)trimethylsilancs,

the

178

JUNG

reactivity

also increases.

product

was observed

AND

YOO

But no ((trin~ethylsilyl)n~ethyl)benzene in the alkylation

with

reactivities

of(chlorinated

alkyl)silanes

increase

the carbon

of (chlorinated

alkyl)silanes

increase

to (dichloromethyl)chlorosilane

as an alkyluted

(chlorornethyl)trirnethylsilanes.

The

as the numberofchlolo-groups fl-om

on

(chloromethyl)chlol-osil~une

to (trichloromethyl)chllol~oail~ne.

V CONCLUSION Studies

on

compounds alkenyl aromatic Si-Cl

the alkylation

reaction

are summarized

and chloroalkyl hydrocarbons bonds

are expected

PROSPECTS

of aromatic

in this review.

groups

can be applied Such

starting

organosilicon

materials

compounds

A variety

to give the corresponding

as functionality. to be useful

AND

with

of chlorocilanes

in the Friedel-Crafts aromatic compounds

lor the silicone

organosilicon containing alkylations

compounds with industry.

of

containing Si-Cl

bonds

Friedal-Crafts

Alkylations

with Silicon Compounds

179

180

JUNG AND YOO

ADVANCES

IN ORGANOMETALLIC

CHEMISTRY,

VOL. 46

Transition-Metal Systems Bearing a Nucleophilic Carbene Ancillary Ligand: from Thermochemistry to Catalysis LALEH JAFARPOUR

and STEVEN P NOLAN” Department of Chemstry Unwersify of New Orleans New Orleans, Louisiana 70148

I. II. III. IV V.

VI. VII. VIII. IX.

Introduction Thermoch~tnical and Structural Studies Calor-imetric Sttdics Structural Studies Application\ of Nucleold~ilic Carhencs a Cntalq\t Prccurwn ill Homopx~eous Catalysi\ .A. Olelin Metnthesi\ B. Carbon-Cnrhon and Carbon-NitI-oven Bond Formation Swuhi Cro\<mCoupling of Arylchlor-ideb wth Arylboronic Acids. CrowCoupling or AI-ylchloritlc\ with Aryl Griyxd Reagents (Kumada Reaction) Amination of Ar)‘lchlol-ides Coticlu~ion Rrferencc\

1x1 IX.1 1x4 IX5 191 I91 20x 70x 71 I 715 11X 2 I9

I INTRODUCTION

Although tertiary phosphine ligands are ~~sef’ul in controlling reactivity and selectivity in organometallic chemistry and homogeneous catalysis,‘.’ they often are sensitive to air oxidation and therefore require air-free handling in order to minimize ligand oxidation. More importantly. significant P-C bond degradation occurs when these ligands are subjected to higher temperatures which in certain catalytic processes results in the deactivation of the catalyst, and as a consequence requires the use of higher phosphine concentration.” Furthermore, specific applications benefit from or require the use of sterically demanding phosphine ligation to stabilize reactive intermediates.‘-’ Therefore, there is a need for strongly nucleophilic (electron-rich), bulky ligands that are resistant to oxidizing agents and form stable bonds with metals.

181 At1 rights

Copyright ‘~8 2001 by Academic Press. of reproduction in any form reserved. 006%3055/01 $35.00

182

JAFARPOUR

Nucleophilic

carbene

compounds carbon.’ with

that

have

In other words

negligible

imidazole

n-back-bonding

the saturated reports

but no carbenes

were

disubstituted

These

imidazolium

cult compared

donor

a carbene

I ).‘I Although

ever isolated

ligands

nucleophilic

and palladium as catalyst

carbenes

to that of an isolable

as alterna-

that the electron-rich center

at the carbon

cen-

was on

C4 and CS). there are some

in any of these early rhodium

on the ligands

much of his work

bond between

in desulfuriring imidazolium

systenia.‘J.‘5 complexes

I .3salts

Herrmann bearing

I ,3-

in Heck coupling

precursors

arc generally

salts (Eq. ( I )): thus their general

ML,B

two-electron

” ” He succeeded to produce I .?-disubstituted

iliiidazol-2-ylidcnes

reactions.‘“.”

charge

analogues.

have synthesized

carbon

no formal

As such they can bc viewed

(Fig.

ring (no double

imidazole-2-thiones

and co-workers

as neutral.

be able to stabilize

unsaturated

and

was the first to recognize

the two nitrogens

imidazoline

involving

disubstituted

their

should

are two-coordinate

electrons

tendency.

’ WanLlick

framework between

imidazo-Zylidenes

nonbonding

they are considered

tives to phosphincs.“-’ ter situated

liganda two

AND NOLAN

generated

use in catalysis

irz .sit~ from becomes

difti-

ligand.

(1)

+ HX.B

+

‘R

M = Rh, Pd B = weak base

Arduengo carbene tection synthesis zolium I .3Bis( reacting

and co-workers

functionality from

with

carbene

of imidazolium

have sterically

degradation

solved

pathways.‘x

salts that allows

salts that were not previously

the isolation

demanding

They

presence of a catalytic amount of dimethyl benes have been used to isolate homoleptic platinum complexes analogous to M(PCy?)?,

which developed

the production

accessible

I -adamantyl)imidazole-2-ylidene the corresponding imidazolium

problem

groups

by conventional

by flanking provide

steric

the pro-

a new

one-step

of substituted

imida-

routes

(Eq. (2)).”

was the first stable carbene isolated by chloride with sodium hydride in the sulfoxide (Eq. (3)).” Arduengo’s carl4-electron bis(carbene)nickel and where M = group IO metal centers.“”

Nucleophilic

183

Carbene Ancillary Ligand

-Hz0

2 RNH,

+ HCOH

+ HX + ‘---/e 0

(3)

‘0

THF

+ Hz1 + NaCI/

(3)

DMSO

R = 1 -adamantyl

Adducts

of a related

carbcne

ligand

with

Group

2 and

I2 mctallocencs

have also

has been the subject

of many

been reported.” The stability theoretical

of these bulky

studies

ring. electronegativity the large t’orwtird bcnes

to explain because

stud& tron

lographic

the stability

from

carbon

indicate

bond

the nitrogen which lengths

complexes

bonding

follows

with

nucleophilic

the formally more

these

a

but appear

journey

carbene

p(r)

in this arena

ligands data in predictin

from

These

orbital

X-ray ligands

01‘

crystalhhow

and ab initio

in these ligands.” to be more

carbenc

in homogeneous

vacant

bonds

show

of these caris due to elec-

nucleophilic.J’

of single

and

investigations

in the stability

can also bc isolatcd.4’

is not significant

phosphincs

account

to applications

Further

factors.

have been put

of these carbencs

bearing

are in the range

to the use of these thermodynamic reactions

into

the carbcne

kinetic

(80 kcal/mol) factor

stability

pairs

makes

in the imidazolc

stcric effects.

imidazol-2-ylidcnes

that the unusual

that rr-back

dealing

the nitrogens.

of these li~ands?”

saturated

;Lre similar to the tertiary 43 ligands. The present

carbenes

such as the r-interaction

is not an important

data of the metal

M-Qcarbene)

studies

from

stabilization

stable

donation

factors

gap in imidarole-2-ylidenes

indicated

also

the carbene

also

effects

singlet-triplet

that the resonance

nucleophilic

and several

These

that

studies ligands

strongly

coordinating

solution

calorimetric

in an organometallic g the feasibility

system

of exchange

catalysis.

II THERMOCHEMICAL

AND STRUCTURAL

STUDIES

Tilley and co-workers reported the isolation ofcoordinatively plexes Cp*Ru(L)CI (Cp* = $-C5Me5. L = PCy3 and P’Prj) with

the tetrameric

species

[Cp*RuCl]+”

This

synthetic

by

pathway

unsaturated comsimple rcacGon

a

has allowed

us

184

JAFARPOUR

to measure

the binding

goal of describing bene ligands, the binding The

of these two bulky

the stereoelectronic

we conducted

properties

a thermochemical

of these imidazole-baaed

versatile

demanding ligands

affinity

starting

phosphines

AND NOLAN

material (PCy,

to the Cp”RuCI

[ Cp’RuCl

]J (I)

(L) to give deep blue, coordinatively

cyclohcxyl

(Icy,

6); 45dichloro-

With

2);

study

the car-

dealing

with

n,oiety.J7 rapidly

with

Cp”Ru(L)CI

sterically carbene complexes

I ,3-R7-i,nidazol-3-ylidene

( ITol, 4): 4chlorophenyl

I ,3-bis(2,4,h-trimcthylphenyl)

diisopropylphenyl)imidazo-2-ylidenc

ligands.‘”

the nucleophilic

unsaturated

(IMes.

3); 4-methylphenyl

reacts

as well as with

2-8 (L = I ,3-bis(2.4,6-trimethylphenyl) (IAd,

and structural

ligands

and P’Prj)

phosphine

of a series of nuclcophilic

(IPCI.

(IMesCI.

(IPr. 8) in high yields

=

5); adamantyl

7); and I ,3-bis(2.6 according

to Eel. (3).

.. Ry,( 1/4[Cp’RuCl],

, R

1’71

THF

+

r=p X

x H H H H H i’

CALORIMETRIC The

reactions

depicted rapidly

The solution

calorimetric

values

determined

were

in Eq. (I)

L IMfZS ‘CY ITO1 IPCI IAd IMesCl IPI

are suitable

8

for calorimetric

as monitored

has been described

by anaerobic

2 3 4 5 6 7

STUDIES

and quantitatively protocol

(3)

X

R mesftyl cyclohexyl 4.methylphenyl 4-chlorophenyl adamantyl 2.4.6.trlmelhylphenyl 2.6~dllsopropylphenyl

since they proceed

Cp’Ru(L)CI

solution

investigations

by NMR

elsewhere.”

calorimetry

reacting 4 equivalents of each carbcne with one equivalent of this study are presented in Table I.

spectroscopy. The enthalpy

in THF or tetramcr.

at 30 C by The I-esu1t.s

The enthalpies of reaction can be converted to relative cnthalpics of reaction on mole of product basis by dividing the enthalpies by 4 which represents the number of bonds enthalpy

made values

one for another

in the course

of reaction.

in Table I represents ligand

listed.

With

The

the enthalpic the exception

difference driving

between

two

relative

force for a substitution

of IAd (6). all reactions

a

of

involving

carbene ligands show more exothermic reaction enthalpy values than do PCy; and P’Pry. From the relative enthalpy data it is apparent that Cp*Ru(PCyj)CI should undergo a substitution of phosphine ligand by nucleophilic carbenes with more

Nucleophilic

TABLE

IMc\ IC\i ITol IpCl IAd IMtYC‘I I PI PQ 3 P ‘l’r,

exothermic

185

Carbene Ancillary Ligand I

I 07 I .h7 0 09 I .03 I .-I’) I .Oh 1.20” I .38” I .33”

I S.h 21.7 IX.8 I X.6 6.X 12.1 I I.1 IO3 0.4

Q.h(O.2) x5.010.7) 75.3CO.1) 73.3(0.3) 37.40.3) 1X.5(0.4) US(O.4, 4 I .9(W) 37.40.3)

reaction enthalpy and it is indeed the case (Eq. (5))

Cp’Ru(PCy,)CI

THF

+

*

Cp’Ru(L)CI

+ PCy,

\--/ L IME ICY IT0 IPCI IMesCl IPr

R mesltyl cyclohexyl 4.methylphenyl 4-chlorophenyl 2.4.6.trtmethylphenyl 2.6~dilsopropylphenyl

(5)

IV STRUCTURAL

STUDIES

The enthalpies of reaction for nucleophilic carbenes depend on the stereoelectronic properties of the ligands affecting the availability of the carbene lone pair. I I An example ofelectronic influence is the 3.5 kcal/mol enthalpy difference between the isosteric pair IMes and IMesCl that shows the electron-withdrawing nature 01 Cl compared to H. This trend again is in line with electron donor/withdrawing ability of arene substituents. The effect in this last case is a long range electronic

JAFARPOUR

186

efl‘ect

and is relatively

carbene ability

ofthe

carbene

more exothermic adamantyl effects steric

congestion

IAd

system. 7”“,

group

The case in point which

separating

structural and

ligands. studies

smaller

carbon

is the ICy which

of ligand atom

metal-lone

were carried 2-8)

and

examined.

substitution.

compared

Increase

a closer

pair overlap.

out on samples were

investigated

ligand

hinders

and the the donor

is some 5.6 kcal/nml

carbene

of the clcctronic properties To gauge the steric tk~ors

9’” (Figs.

the aryl

in lieu of an aryl increases

is the Icast exothertnic

the carbene

affording

a clear picture

as ancillary 8”‘.

of the distance

of this low cnthalpy

around

therefore

offer

moieties

an alkyl

ligand.

are at the origin

results

in \;iew

than IMes. The other alkyl-substituted

derivative

the ligand,

6”.

small

lone pair. Substituting

AND NOLAN

is the Steric in the

approach

of

The calorimetric

of the nucleophilic carbene at play in the Cp*Ru(L)CI of complexes with

2J”. 3”,

the structural

417. data

Nucleophilic

FK;. 1.

Molecular

structure

187

Carbene Ancillary Ligand

of Cp*Ru(lTol

K’I (4). Hydrogen

atom\ we otnittcd

for clarity.

already available for Cp*Ru(P’Pr~)Cl”. Selected bond angles and bond lengths are presented in Table II. Ru-C(carbene) bond distances are shorter than Ru-P bond lengths. but this can simply be explained by the difference in covalent radii between P and C.“’ The variation of Ru-C(carbene) bond distances among ruthenium carbene complexes illustrates that nucleophilic carbene ligands are better donors when alkyl, instead of aryl. groups are present, with the exception of 6. This anomaly can be explained on the basis of large steric demands of the adamantyl groups on the imidazole framework which hinder the carbene lone pair overlap with metal orbitals. Comparison of the Ru-C(carbene) bond distances among the q-substituted carbenes show

FK;. 5.

Molecular

structure

ofCp*Ru(lAd)CI

(6). Hydrogen

atoms are omitted

for clarity

188

JAFARPOUR

that the least sterically The difference sults from an absolute the existence

carbcnc.

in the aforementioned

the electronic

kept in mind

encumbered effect

of the bond

of significant

bond

ITol,

has the shortest

length

between

of Cl imidazol-2-ylidene

here that the enthalpy gauge

AND NOLAN

of reaction

disruption

reorganization

energy

be directly

of the Ru-Carbene as depicted

bond

length.

and IMesCl

substituents.

cannot

energies

IMes

re-

It should converted in view

by variation

be into of

in the

Nucleophilic

189

Carbene Ancillary Ligand

FK;. X.

Ru-Cp”

and Ru-Cl

reorganization complexes

bond

energy

3 and 4. Here.

yet the Ru-C(carbene) between

distances.

is evident complex

distances

the two complexes

(‘ornplcx

Carbcne Strric\ (AI and AH)

2 3 3 6 7 x 9 10

150.7. 126.7. 155.2. I-w.0. IS2.0. 133.0. 115.x IO0.X

70.4 3 I .x 30.x 1 I .4 69.9 137.6

“Replace

C tiith

P

A very clear example

when

comparing

3 is more are statistically

resides

Ru-C

Ku-Cl

2. IO5 1.070 2.06X 2.153 2.073 3.0X6 2.383” 2.3YS”

1.376 2.523 2.340 2.438 ‘37.5 2.371 2.378 2.365

the Icy

stable

than 4 by some

identical.

in the differences

Ku-C)‘: I.766 I.658 1.755 I.778 I.765 I.751 I.771 I .x IO

of the presence

C-Ru-(‘I 90.6 93.7 06.0 x7.9 YO.0 x9.32 Yl.2” Y I .1”

of this

and the ITol containing IO kcal/mol.

The largest

in Ru-Cp*

difference

centroid

C-Ru-CI)“’

Cp.‘--Ku-Cl

I40.7 I2Y.3 I3O.X llX.7 142.0 111.5 I3X.Y” I jY.2”

I X.6 1s.s 132.x I30.1 12x.0 12’1.2 129.9 I2Y.3

bond

190

JAFARPOUR AND NOLAN

distance

[a differences

distance

(a difference

tron density carbene Here,

I8 A with 3 being

has been pushed

ruthenium

is evident

of 0.1 k with 4 being of0.

arc examined,

appears

to be a small

differently.

W C propose

to the presence an acceptor) substituent

the effect effects is absent.

the position

on the carbenc present

in Table

I ppm while

the alkyl derivatives

frequency.’

I. The

to greater

No straightforward

tors have been qualitatively light as phosphinc defined

the stcric

the steric effects directly

from

the method Numerical in Table

length

It would

since a cone angle

can be made

energy.

cannot

(as defined

on the of highet

The steric fat-

be of USC to quantify

They

around as good

density

correlation

is

which

the stcric

be viewed

in the same

by Tolman”)

cannot

hc

In terms of steric effects, the nuclcophilic carbenes with “length” and “height.” As ;I first model to as “fences.”

can be considered describe

addressed.

ligands

electron

of the rcorganiation

this class of ligands.

in the present

increased

center

are known

shifts of the Cp’ resonance

bond strength/bond

in view of the presence

characterizing

The

on the carbene

this explanation

complexes which

as

the large

of these complexes

phosphines

affords

can be attributed

a ,7 system

carbene

(including

dis-

hchave

(or contributes

supporting

spectra

trend above.

bond

carbenes

in turn diminishes

cases where

aryl-substituted

shielding

and RLI-Cp’

localizes

which

piece ofevidence

are at GI. I.5 to I .7 ppm.

Cp” ring leading in this system

Ii&and.

in the ‘H NMR

are reported

discussed

in bondin, u behavior

in the alkyl

An additional

vs enthalpy

substituted

in the aryl case which

of the Cp” protons

ligands)

and alkyl

bond

that the elec-

the aryl-substituted

explanations

in the Ru-Cl

Aryl-

that this difference

of a n system

reorganization

variation

to the other.

When

the Ru-C(carbene)

and makes sense in terms of the electronic

there

factors

than 31 and the Ru-Cl than 4). It appears

back into the Cp” ligand.

complexes

tances from one complex

donor

longer longer

system.

profile.

afforded

we propose by this ligand

the crystallographic used to extract values

defining

II. Not surprisingly.

that two

parameters

class. These

be used to quantify

two quantiticc

data. The two views

presented

can bc taken in Fig. 9 depict

the two parameters. length

and height

all aryl-substituted

of the carbene carbenes

“fences”

possess

nearly

are listed the same

Nucleophilic

Carbene Ancillary Ligand

191

large Al, value since the ‘.length” of the ligand is measured using the aryl para methyl group. The magnitude of the “height” parameter (An) depends on the presence or absence of ortho substituents. The most demanding aryl-substituted carbene ligand is the IMes ligand with I SO.7 (A,~) and 70.4 (AH) as stcric parameters. The alkyl-substituted carbene Icy is the least sterically demanding ligand investigated in the present series. The IAd ligand, although bearing sterically dcmanding adamantyl groups, has an Al, parameter comparable to the aryl ligands examined and a smaller An parameter. The Icy ligand appears to be unique in the herics investigated. In complex 3. the AL angle is 126.3 In the phosphine complexes !, and 10 these angles were measured as I IS.8 (8) and 100.8 (9). The ICy is sterically more closely related to these two phosphine complexes.

APPLICATIONS OF NUCLEOPHILIC CARBENES AS CATALYST PRECURSORS IN HOMOGENEOUS CATALYSIS A. Olefin Metathesis

The last decade has witnessed the growing use of’ olefin metathesis in organic synthesis.‘ 54-sL’Ring closing metathesis [RCM, Eq. (O)] and ring opening metathesis [ROM. Eq. (7)] as well as a combination of these transformations have resulted in providing opportunities to build molecules of interest and importance. M=kJ=

-0’;

!\ 0 +!4 I=’M=To--R.

(6)

(7)

Catalysts of the Grubbs type (benzylidene and vinylalkylidene) are of special interest, since they are only moderately sensitive to air and moisture and show significant tolerance of‘ functional groups.““-“’ The ruthenium carbene complex. RuCI,(=CHPh)(PCy~)z (II), developed by Grubbs et trl. is ;I highly efficient catalyst precursor and its use is widespread in organic and polymer chcinistry.“.““~“” We have shown that most of the substituted imidazol-2-ylidene ligands studied form stronger covalent bonds to the ruthenium center than PCy3 (\kk .SU~IYI). Therefore. it is possible to replace one or both of the phosphine ligands in 11

192 with

JAFARPOUR nucleophilic

ancillary Since

carhene

phosphine we have

donors

electron

curhcnes

that

than

donor

imidazol-2-ylidene cations

donor

determined

IPr are better creased

ligands.4q.7”

electron

only

CM

It has been noted that an increase in the leads to increased catalytic activity.4

imidazol-‘-ylidcne

carbencs

such

as IMcs

and

the catalytic behavior should reflect this When both of the phosphincs were replaced

they showed

and RCM.70

one PCy:

”

ability

PCY;~“.

ability.

ligands

to ROM

AND NOLAN

llpon

is replaced

PCY, 1 &’ H R”+=c* + ‘Ph I PCY,

only

using

littlc

it’any

sufficiently

improvements bulky

inby

in appli-

irnidazol-2-Slidenc

(see Eq. (X)).47+J~5”

i

\+cl H Fb=c“ ‘Ph 1 PCY,

L -Cl4

+ PCY3

(8)

11 L = IMes, 12 L = IPr, 13

The

identities

studies.

are presented The a nearly

of 12 and

Structural

models

in Figs.

structural linear

13 were

IO and

analyses

confirmed

by single

of 12 and 13 along I 1 and Tuble

reveal

CI( I)-Ku--Cl(Z)

distorted angle

with

crystal

selected

X-ray metrical

diffraction parameters

111, respectively. square (16X.62

pyramidal and

170.32

coordination for

12 and

with 13,

Nucleophilic

193

Carbene Ancillary Ligand

respectively). The carbene unit in each structure is perpendicular to the C( I )-RLI-P plane. and the carbene aryl moiety is only slightly twisted out of the Cl( I )-RuCl(2)-C(carbene) plane. The Ru-C(carbene) bond distances (I .841( I I ) w and I .8 I7 A for 12 and 13, respectively) are the same as in RuC12(=CH-/Xf,HICI) (PCy:)? (I ,838 (3) A)” and mqinally shorter than in RuC12(=CHCH=CPh7)

%t.t~l I:I) HONO LkucirHs (A) hw ANGL.~S(kg) fw (PCy)) RuCI~(=C(H)Ph)(lMe\) (12). (P(‘yI)RuCl~(=C(H)Ph)(lPr) (13) ANo (PCypl)RuC12(=CHCH=CMe2)(1Me) (14) 12

13

I4 2.0X1(3) 2.4Ol’( IO). ‘.3’m(x)

1X41(1 I) 2.419(3) 90.1(S) 97.1(J) 103.3(5). X7.1(5) x9.s I( 10).89.86(91 WJ(3). X6.9(3)

2.0X8(2) 2.3X21(7). 2.400X(7) 1X17(3) ?.1554(7) 97.m IO) 06.64(X) 90.49(9). X8.X7(9) 03.Ohl2), OO.S9(2) W.lh(6). X3.77(6)

Ku-C(L) Ku-CI( I .2) Ru-C(cxbm) Ii II-P C(cn~bcnc)-Ru-C(I~] (‘(cxhcw-Ru-P C(~ortxw-Ku-CI( I .?I I’-Ru-CI( I .2) C‘(I>)-Ru--(‘I( I .2)

I .7641-1) 2.14X7( IO) 102.46( IS) os.ssll3, 91. I(,( 171.07 37( 17) W.33(1). X7.3q-l) X9.0X(7). X6.7.5(7)

JAFARPOUR

(PCy;)?

(I .X5 I (2 I ) A).” While

12 and

13, they

I .X4 I ( I I ). and clearly

display

dcne and II datively two-electron ligands

donor.

arc sterically

two

two (formally)

different

Ru-C(L),

distinguish

Ru-C

2.069(

From more

carbenc

distances

I I ) A).

metal-carbenc

hound

AND NOLAN

These

important

interactions:

IO and

demanding

arc praent

metrical

parameters

bound

the latter acting

I I. it is ulso clear

in

in 12 Ru-C(carbene).

a covalently

imidazol-2-ylider~~-~~l~-bene, Figs.

fragments

(e.g.,

bcnzylias a simple

that the IMcs

and IPr

than PCy;.

The exchange reaction of one phosphine ligund (PCyp-(, Cyp=cyclopentyl) in (PCyp3)2RuC11(=CHCH=CMe2) with [Me:, results in the formation of (PCyp;) Ru(lMes)C12(=CHCH=CMc,) ized by X-ray crystallography. bond lengths and bond angles

(14).”

This compound

A structural are presented

was structurally

character-

model of 14 along with some selected in Fig. I2 and Table Ill. The metrical

data for compounds 12 and 14 show similar bond distances and angles (Table 111). The coordination sphere around the metal center corms a distorted square pyramid with

the bcnzylidene

and vinylmethylene

moiety

at the apex.

tance of the apical carhenc cnrbo~~ to the metal center 12. Therefore. it cm be inferred that the vinylmethylene

However.

the dis-

in 14 is shorter than that in moiety is more strongly

bound to ruthenium than the benzylidene. All other bond distances around the metal center are slightly longer in 14 than in complex 12. The bulk of the fence

Nucleophilic

created

by the IMes

the bond

angles

The catalytic the standard Table

activity

RCM

lV.‘7.‘“-5”

complexes

ligand

ofthese

Moreover.

12 and

new complexes

the thermal

13 and Results

14 were

imida~ol-2-ylideri~

analogues

catalyst

displaying

precursors,

to those of existing

Grubbs the saturated

imidazole

lute into an increased

reactivity

13).‘? They

compared

analofues. Recently,

ring

closing

bearing within

catalyst I and 2 h.

In fact their decomposition

preliminary

system

shows

s~dy

can act as olctin

and improved

version

that the

metathesis

thermal

stability

of ilnida~ol-2-ylidenes.

proposed

that the higher

to its unsaturated

of the desired

(RuCI~(=C(H)Ph)(PCy3)(

increased

robust.

activity

the saturated

(Fig. ligand

phosphine decompose

catalysts.

rt trl. have prepared

dihydroimiazol-2-ylidenes

formed

signiticant

in

bearing

lo that of‘ 11 and (PCqp~)~RuCI1

Thih

of the Grubbs

are shown

of the imidazol-2-ylidene

(=CHCH=CMel)

at this ~cmperature.J”.s”

and 14) was tested by using

the original

at 60 C. 12, 13, and 14 are more

:.md causes

(Eq. (c))).‘Rcsults

compared

show that where

moiety

III).

(12,13,

stability

starts after 2 weeks

compared

with the carbene (Table

diethyldiallylmalonatc

11 and (PCyp~),RuCl~

respectively,

interferes

large deviations

substrate.

(=CHCH=CMez). precursors

sterically

to undergo

195

Carbene Ancillary Ligand

catalysts.

analogues

would

The ruthenium

activity

compared

lo

their

ol

trans-

complexes

I .3-R2-4.S-dihydroilnidar.ol-2-yliden~~))

metathesis

4,S-

basicity

showed bis(phosphine)

73

the

than alkylidencs

possibility might

that

also serve

complexes as catalyst

..

of unsaturated precursors

“C,”

in olofin

ligands metathesis

other has

196

JAFARPOUR

rcccived

more

cymene)RuCIl

attention. (PCyj)

[ ( p-cymenc)KuCI(PCy;) for various stcrically active

intermediates.

in THF

and electron Hence,

and

room

results

(I’-“yliiene)RuCII(IPr)

to synthcaize

[ ( />-cymenc)KuCI1ll in the I’ortnation

of [( p-cymenc)KuCI(IMes)(=C=C=CPh2)1PF~, The X-ray 20 is shown

struc(ure

of20

in Fig.

I4. The

coordination

in olefin (17)

geometry

metathesis.

with

IMes

of ( p-cymene)RuCI,(

and around

structural

the Ru cctlter

THF

T

IPr

Cl

Cl /

OH PFs *

‘Ph

Cl / IMS 20 S('Hl.Ml

i

%

IMes

Ph *“xC=C=C’

IMes)

I ).” a

IML’,

Cl /

or IPt

Treating 18 with I 1 Iresults in the formation

(20) (Scheme

has hccn determined

crystal

precursors

the imidaLol-2-yliderie

activity

(19) in good yields. in the presence of NaPF(,

alcohol

catalyst

example mentioned above tiic use 01 phosphines is required to stabilize rc-

In every donuting

available

been shown that (/Iallenylidcnc derivative.

are aclivc

and test their catalytic

temperature

diphcnylpt-op-?-ynyl

it has 1 X-electt-on (16).

it is oi interest

of commercially at

example.

(=C=C=CPh,)]PFc,

of‘ these complexes

Reaction

kJl-

and its cationic,

reactions.71.75.70

demanding

analogucs

(18)

KCM

72.7J-7x

(15),

AND NOLAN

NaPF, CH,OH

Cl

model can

01‘ be

Nucleophllic

considered

as a three-legged

‘I h fashion,

the isopropyl

center,

presumably

the IMes

ligand

reactions.

and bond

The catalytic

steric stcric

is bound

;lre distorted factors.

to ruthenium

away

from

The two mesityl

center

with

crow,din, (7 which

groups

the dihedral appears

in ;I

the metal on

an&s

beneficial

in

is not linear but rather bent at the middle is = I7 I .8 ). The Ru-CLL‘33 (I .890(4) A) bond distance than the Ru-Cl0 sin& bond (2.077(4) A). Selected bond

angles activities

(PR?) (R=Cy

p-Cymene

the ruthenium

(2) providing

strate, dicthyldiallylmalonatc KuCll

toward

The allenylidene

carbon (C22-C23-C24 considerably shorter lengths

stool.

on the arene

due to unfavorahlc are bent

of 7X.2 (2) and 89.9 RCM

piano groups

197

Carbene Ancillary Ligand

group

are reported

in Table

(Scheme

(21) and i-Pr (22)).

RN I )-C(E) Ru( I )-C( IO) Ru( I )-UN) Ru( I )-c-(40) Ru( I )-C(3XI Ru(l )-c‘(37) Ru( I j-U:‘: Rut I )-(‘I( I) Ru( I )-(‘(A:, Ku(l)-C(1l)

V.

of 7, 8, and 9 have been tested

I .XYO(4) 1.077(-L) 1.123(S) 2.219(4) 2.3.56(1) 2.3X7(4) I .X03(4) 2.1903 I I ) X46(1) 2.25X(3)

111) and compared Results

by using

arc presented

C’(22)-Ru( I I-c’I( I ) CC?‘)-Ru( I I-c‘( IO) (‘( IO)-Ru( I )-CI( I) C(2’)-C(23)-(‘l’4) O-RwC(31) ct !-Ru-ctSY) Ct-“-Ru-CI( I)

the RCM

sub-

to those of (p-cymene) in Table

X4.W( I 2) Y2.67( IS) xs.ixi I I) 17l.N-I) 131.x 172.‘) 115.1

VI. When

198

JAFARPOUR

the reactions 9 with

were carried

a conversion

21 and 22 as catalyst 17 hours

(Table

perature

(40%

containing light,

yield,

Table

was observed

Performing

the reactions

(Table

VI entries

arc not photo-induced.

led to the yields

of48

and 47%.

VI entry

of those of the phosphinc

3) was in the range

the role of solvent,

18 and 19 as the catalyst

at’ter only

mixtures

4 and 8). which

would

is in contrast

with

indicate

and yields

that the catalytic

the complexes

catalysts

irradiation.x”

only

when

activated

by UV

7 and 9). of‘the rereactions

01‘ the type

active

in the presence

conversion

VI entries

the outcome

and

and dx-toluene

to X0 C. a 100%

2 h in both cases (Table

in the dark did not change

temperature,

precursors

have been reported

that RCM

aticl

of‘ 19 at this tem-

PR;) (M = Ru. OS; R = Cy, ~-PI-) which

ROM

The use of

respectively.

cymene)Cll( reported

reaction

of 78%.

activity

with

This

to 40 C. 20 catalyzed

a conversion

I . 3, 5, and 6). The catalytic

heatin, ~7 the reaction

Upon

to product actions

and heated 18 showed

21 and 22. To investigate

was pert‘ormed

as the solvent.

whereas

precursors

VI entries

complexcs

RCM

out in CDlCll

of 85%.

AND NOLAN

M( /I-

to become

It has also been

of [ ( p-cymene)(PCy~)ClRu=C=C=CPh~]PF~,

and Ru( p-cymene)CI~(PCyi) i$ accelerated by cxposurc to UV or neon light.75.7” No such et’fcct is observed l‘or our system. Examination ol‘ data gathered in Table VI shows that the IMes containing complexes 18 and 20 are the best catalyst precursors found in this study whereas the ruthenium 19, showed reactivity similar to those of21 data the IMes

complex incorporating the IPr ligand. and 22. From the solution calorimetric

ligand proved to be a stronger binder than IPr ligand whose relative The initial step in the ring closing cnthalpy is comparable to that of PCyl ligand.” metathesis mechanism Losing the ( p-cymene)RuLClz complexes must involve the and in the cast ofruthcnium-arenc formation of a ruthenium-carbcne complex;““.”

Nucleophilic complexes ticity

the carbene

moiety

of the arene ring,

ligand

(IMes)

phines,

can presumably

leading

can facilitate to those

to explain

to X0 C both

18 and 19 show the activation

ligands

and under

easily

the origin

than either

of the higher

the same activity.

barrier

in the hapdonating

IPr or the phos-

catalytic

activity

the temperature

It could

for the change

be argued

in arene

the electronic

in developing

of the previously

synthesized

(=C=C=CPhz)(PR3)2, RCM

the “C,,” cyclizcd

R=Ph,

activity

complexes.

to those

Analysis

of

is raised

that at higher

hapticity

has already

differences

vinyl

betwecn

the

and

16) and clearly compound. quare

in this complex

complexes

show

pyrami,

ing the unique

apical

geometry

with the strongest site. The

square

the donor

atoms

of the phosphine

ruthenium

center

lying

().293(X)

allenylidenc

reactions

2).“.”

showed crystal

determined

of Ru to an indenylidene around n-acidic

the ruthenium ligand

base is defined

(Figs.

15

moiety.

Jn

center

(indenylidene) liEand\

12) A in 28 above

R = Ph, 25 R = Cy. 27

R = Ph, 23 R = Cy, 24

R = Ph, 26 R = Cy, 28

;I

struc-

is disassum-

by the two chlorides

and the iinidazol-~-ylidenc i\ in 26 and 0.3443(

that

but rather

The X-ray

been

RuCI,

and in comparing

ruthenium

is not an allenylidene

26 and 28 have

the coordination

the r>nordination

reactions

substitution

(Scheme

ana-

complexes,

1%electron

of simple

“an indenylidene”

of the IPr bearing

of imidazol-2-ylidcne

Ru-allenylidene

Cy7” via substitution

moiety

carbene

the synthesis neutral

of the cationic

of the product

unsaturated

each torted

more

these conditions

We were also interested

tures

by the change

are not very important.

logues their

be formed

sites on Ru. The more electron

of 19, 21, and 22 at 40 C. When

temperatures been overcome

to vacant

this process

and this is proposed

18 compared

199

Carbene Ancillary Ligand

with

and the

this plane.

200

JAFARPOUR AND NOLAN

Nucleophilic

KU( I )-C(3) Ru( I 1-Q 13) Ku( I )-CI( I ) Ru( I )-Cl(Z) Ru( I )-PC I ) (‘m-c(‘c)) C(29)-c’(30) C(X))-cc.? I ) CC.31 )-C(32) Cl32)-C(X) c-(33)-C(3)

The Ru-CJindenylidene) length

between

A vs 2. IO2(3) and bond

angles

Investigating

I .397(S) I ..%w5) l.S17(S) I .J7X(5) I .iO7(~) lO4.J7( I?) OX.lO( IO) x4.38(81 02.55( IO) 1(,2.08(8~ 167.15(3)

(‘(33)~C(M) (‘(3S)-C(3h) ux-C(X) U.w-(337) cc3 I )-C(M) (‘(2X)-Rut I )-C( 13) c‘(?X)-Rut I )-CI( I ) C‘(lIikRu(l)-Cl(Z) C‘(?X)-Ru(I)-P(I) C‘(l3)-Ru(I)-P(I) (‘I( I)-Ru( I )-Cl(2)

distances

are significantly

for 25 and 27 are presented thermal

PCy3 bearing IX, entry

I -ene) (27) (Table temperature.

VII

and the weaker

stabilities

n-acid

shorter

analogues

VII and VIII,

23-28

PPhj i.e., 23,25,

revealed

(I .852(3) bond

lengths

respectively.

that when

heated

and 27, were less stable than

(24, 26, and 28, respectively). I -ene) (23) which

than the bond

imidxol-2-ylidene

in Tables

of compounds

containing

(PPh3)~Cl2Ru(3-phenylindenylid(Table

TABLE

201

Ligand

,& in 26 and I .86 I(4) r\ vs 2. I 13(J) A in 28). Selected

to 80 ‘C the compounds their

Ancillary

I .X52(3) 2.102(3) 1.3X9.5(9) 1.3688(X) 2.3977( IO) I .356(1) I .337(S) I .383(S) I .377(S) I .306(7) I .379(7)

bond

the ruthenium

Carbene

The least stable

decomposed

was

after 2 h at 80 ‘C

I) and the most stable was (lPr)(PPhj)Cl2Ru(3-phenylindenylidIX, entry 4) which

It can be concluded

showed

TABLE

Ru( I )-C(28) Ru( I )-C( 13) Ru( I )-CI( I ) Ru( I )-Cl(2) Ru( I )-PC I ) C(‘X)-C(X) c-(20)-C(X)) C(XWC(3 I) c’(31)-C(31, C(32)-C(33) C(31)-c-(34,

decomposition

that the presence

1.X61(3) 2.1 13(J) 23X33( I I ) 2.3903( I I ) 2.-1X4( I?-) I .-171(6) I ..3.50(6) I ,.&X4(6) 1.381(6) I .-m( 7) I .i7’)(7)

after 42 h at the same

of the nucleophilic

VIII

C(34)-C(3S) (‘(35)-C(M) C(281-C(X) C(30)-C(37) (‘(31)-C(M) C’(ZX)-Ru( I I--c( 13) U1X)-Ku( I )-CI( I ) UI3)-Ru(I)-(‘I(Z) (‘(2X)-Ru( I )-PC I ) C(I3~-Ku(I)-P(I) CI( I )-Ru( I )-Cl(Z)

I .3X7(7) I .37X(6) I .-w(6) I .173(b) I .-w(6) 102.17(17) lOO.li~ll) 90.16(1 I) 96.59( 13) I61 29(12) 163.50(3)

carbene

202

JAFARPOUR

AND NOLAN

TAKLE TIII:I<\I.II.

S IAI~II.I

23-28

I

ligand

IPr in the coordination

cantly.

The complexes

pose at elevated involves

malonate

(29),

23-28

Three

diallyltosylamine

(30). solvent.

in Table

monitored

by integrating

the results

are presented

in Scheme

3.

in Table

with

28 (Table

precursors plexes

that

X. entry

in this

X, entries

only when dered

ligand

should metathe-

diethyldiallyl-

tubes

precursor

were then kept at the ten-

and diene peaks

(31)

ofcatalyst

disappearance

in the ‘H NMR transformations

was eliminated

from

were

spectra

I -ene) (26) showed and diallyltosylamine

(29)

be noted

activity

the list of catalyst conI -ene)

precursor

25 can convert

(25)

good catalytic ac(30) as substrata

that 25 catalyzes

26 does so at room temperature. (31) does not easily

and

are depicted

ruthenium-indenylidene-imidazo-2-ylidcnc

heated to 40 C. whereas catalyst

substrates

of5 mol%

X and the catalytic

3, 4, 8. and 9). It should

reaction:

PPhj

in the ring closing

dienc

formation

methylene

diethyldi(Z-methylallyl)malonate

metathesis

pathway

to dissociate)

PCy? moiety.

(IMes)(PPh~)CI~Ru(3-phenylindenylid-

and (IPr)(PPh3)Cl?Ru(3-phenylindenylidtivity with diethyldiallymalonate (Table

IX, entries

1 -cne) (23) did not show any catalytic

The

PPh+

bound

bound

a solution

I ) and therefore

study.

contained

are less likely

precursors

The NMR

(PPhj)QZRu(3-phenylindenylid-

h) (Table

and diethyldi(?-methylallyl)malonate

X. Product

the allylic

signili-

and did not decom-

if the decomposition

ligands

different

tubes containing

deuterated

reported

IO days (256

tightly

the complex

robust

the less tightly

as catalyst

investigated.

in an appropriate

(other

and hence

stabilizes

were more because

faster than the more

were added to the NMR peratures

surprising

ofphosphines

The role of complexes was

of ruthenium PCyi

even after about

is hardly

the less electron-releasing

sis reactions

2 42

sphcrc

temperatures

dissociation

4

incorporating

the dissociation

undergo

PI
A I’x0 c

23 24 25 26 27 2x

2 3 4 5 (1

2. 5. and 6). This result

IX

I’\ 01. (‘~IALYSI

undergo

this reaction Sterically

hin-

ring closing

60% of this substrate

into the

product after 2 h and this is only achieved when the reaction is heated to 80 C. The rate of conversion with 26 is only 17% at this temperature. Heating the reaction mixtures for longer periods of time does not increase the yields of the reactions. it

Nucleophilic

Carbene Ancillary Ligand

203

TABI<E X RING CLOSING

MI:T,ATHI:SIS

RESW~S USING CATALYST

10 RT 10 10 RT RT RT 10 RT RT I(7 X0 x0 x0 x0 80

23 21 25 26 21 28 24 25 26 27 2x 24 25 26 27 28

can he inferred, at higher I -enc)

therefore,

temperatures (24) exhibited

not effective derivatives

with

that the catalyst

(Table

X, entries

high reactivity substrate

31 (Table

is disabled

0 x-l hi 56 xx 75 96 ‘11 0-l 30 x9 0 hh 17 20 I9

2s 25 ,j 2.5 2s 1j 7s 1s 2.5 ,j 15 I20 IX 170 I70 IX

after a certain

period

of time

12-I 6). (PCy;)&Yl2Ru(3-phenylindenylid-

when

used with

X, entries

of (PCyi)Ru(imidazo-2-ylidcne)

phenylindenylid-

PKEX’URSOKS 23-28

substrates

2. 7. and

compounds

S~‘lit:Mt:

3

indenylidenc

(IMes)(PCyi)CIzRu(3-

I -ene) (27) and (IPr)(PCy~)Cl~Ru(3-phenylindcnylid-

E = CO,Et TS = toluenesulfonyl

29 and 30 but was

I?). The

I -ene) (28)

204

JAFARPOUR AND NOLAN

were cotnpalable IPr analogue (27)

to 24 in their reactivity

(28) converted

was much

1 I ). The X. entries catalyst

less reactive

yields

To develop

of ;I better

accessible

from

the 3-phenylby NMR

data).

moiety

indenylidene

4.“j

X-ray

models

five coordinated allenylidene (33),

PCyi

are shown

tnoicty

is located ligandh

are nearly

to 1 .X4 A) for carbene However, mined

these

Ibr cationic

A,. X4 x7 This

identical

moieties

bond

distances

I X-electron

indicates

a

PCyl

of

are summnriad

a

at-e much

better overlap

and

shorter

the

square pyramid.

The

and PCy3 ligands

;I

the Ku-C,,

is in the LISLKII range ruthenium

than

allenylidene

and their

In both structures

the Irons chlorides

in this kind of I&clcutron ruthenium

for IMes

determined

li)rm the base. In both complexes ( I .794( I I ) /i). This

to elc-

ligand

The rcactions

the bond higher

( I .76

complex.i7.“’ Iengths

cotnplexcs

significantly

LISO~

into the

the allenylidenc

ol‘one

as

of PCy2 were

the allenylidene

at the bottom

and

the product

one identified and one unknown

instead

17 and IX. respectively.

at the apex (33).

con-

32 is also

.?..?-diphenyIpropyn-

of 33 and 34 were

is located

led ex-

dcccr-

( I .X7 to I .92 bond

strength

01‘

33 and 34. The comparable moiety to the metal center in complexes bond distances at the base also give very similar valuca indicating no

the carbene tnetnl~ligand signiticant

center

It is interesting

data)

to convert

34 in high yields.

in Figs.

and IMcs

of PPh;

The exchange

structures

reaction

(33).

side products.

acids or by sub-jccting

complex crystal

This

However,

by NMR

,411 attempts

of protic

ruthenium

bond distances

two

were unsuccessful.

the allenylidene

in Scheme

contains

two equivalents

t’ormcd.

by addition

01‘ II-cymcne.

24 (8%

allenylidenc

24. Cotnplcx

17 with

via los\

complex

When was

vated temperatures

structural

data)

(29 and 30).

is the indcnylidcne

to yield

of [ ( /~-‘ymene)RuCI~I1

NMR

(Table

to be good

and Herrn~ann.“’

ruthenium

the soic product PCy;

IO and

with .?,3-tliphenylpropyn-?-ol

tuct

such its PCy;.“”

with

of PCyl

I -indenylic!ene

no carbene

affords

01‘ PCy3,

the rcaction on “P

substrates

by Ct-ubbs73

of‘ true neutral to

X. entries compounds

are shown

unhindered

allowed

substitution

equivalents

(XS% 33 based

(Table

for both 24-28

developed

donatin, ~7 ligand

undergoes

3-01 and two

was

iow

5 and 6). The

the IMes compound

of (PCy1)IRu(=C=C==CPh,)Cl2

in the absence

plex 23 which

ot’ sterically

X, entries

whereas

complexes

complexes

(32)

to the fi,rmation

to note that

31 were

for the synthesis

(PPh;)lRuCI,

in the presence clusively

in the RCM

a method

29 (Table

the same substrate

with

indcnylidene

to the alkylidene

complexes.

(7%

16). The

precursors

cotnparable

toward

of the reactions

IS and

toward

30 with ;I very high yield.

change

tural features

for the electronic

may explain

(vi&j iq%r). The bond than 4 from ideal 90 causes widening

the similar

environment catalytic

of the metal center. properties

of complexes

These

struc-

33 and 34

angles in both complexes at the base do not deviutc more However. steric interference with the allenylidene moiety

of one ofeach

C,-RLI-Cl

angles

(%.2(S)

(33). 95.X9(4)

(34)).

one C,-Ru-P angle (101.4(.5) ) in cotnplcx 33 and the C,,-Ru-C(IMes) angle (%.89(S) ‘) in complex 34. The allenylidene chain is only slightly bent in complex 33 (Ru-C,-C,~ = I75.36( I I ) . C,,-C,-C,, = I75.29( 13) ). This indicates 21

(PPhs)nRuCb 32 2

HCZC-CPh20H

2 PCY,

2 PCy,

CH-C-CPhpOH Hz0

HCEGCPh20H Hz0 p-cymene

4 PPhL, v 23

Cl yy3 Ru=C=C=CPhZ I’CI PCY.! 33 IMS PCYA ! PCYi

Cl. ) Ru=C=C=CPh? I’ IMC,B 34

DT or Hi

2 PCY3 2 PPh3

I PCy, / \ Cl. 1 0= RI= 1 ‘a u pb, PCyz 24

206

JAFARPOUR

strong

conjugation

ing hydrogen shows

significantly

C,-C,j-C,, ligands

along

atoms

stronger

= 167.10( along

rang

and angles

This

the spine

I .26 A (33) and C,j-C;, usual

for ruthenium for complexes

excludin in other

bending

18) ). C-H

may be present.

bond distances

the spine

as observed

AND NOLAN

along

interaction

might

causin g a slight

= I .3S .& (32), allenylidene

LI) BOND

[A ] ,\hl)

Ru-(‘CIMc\,) R LI- I’ Rll-c’i c,,-c,, c‘,I-c‘, C,,-Ku-C? IMe\) C,-RFl’ (‘,,-RlI-(‘l C‘(Ih’le\~-Ru-Cl P-Ru-Cl Ku-C,-C,g c,,-(‘,I-c’:,

= 169.20(

[ C,,-CII

inlluencc

in Table

on the

= I .7-7 A (33).

but these values

K’a7 Selected

bond

are in the distances

XI.

‘r 1 1 I OI< I ,I,. coL1l’l.l:xI.s

II) .

of the PCyl

Xl

Ah\(;I.l

33

R u-c,,

33, however.

atoms

also have ;I weak extension

to neighbor-

Complex

to hydrogen

I .33 A (34)], complcxcs.

33 and 34 are reported

DIS I.,IN(‘ES

?r-interaction

the spine (Ru-C,,-C,<

n-interaction

TABLE SI:I.l:C‘I

g C-H

co~nplexes.~”

33 ,\hlI

34

34 I .79 2.00 2.41 2.37. 2.39 I.20 I .3J 9X.9 02.2 03. I, 9.5.9 8X.9, X9.6 XX.l.‘)l.7 175.1 1752

Nucleophilic

TABLE KING

I 7 3 -I 5 6

Compounds

10 10 30 JO x0

31

34

tl~-loluene

x0

hy ‘H NMR

for complex

thermal

complex

compared

(30),

to the NMR

tubes

.3 and results pcaka

to cationic

significantly as

higher

inferred

catalytic

from activity

after

Both

reaction

bonding

the single displayed

mixtures

25 min

indicated

slightly

activities

Initial

34 after

precursors

substrates,

in Table very

Product

to get detectable

using

conversion

activity

metathesis

reactions ” The center

of the lowel

substrate cithcr

diethyl

complexes

of the other

for the IMes

855, diallyltosylamine 12%. diallyltosylamine

forma-

methylene

at the metal

to 40 C in CD2C12. The turnover

catalytic

in an

complexes.

be at the origin hindered

added

in Scheme

in these

moiety

no sign of ring closing,

closing

XII.

allenylidene

data may

were

the allylic

poorly

(29),

precursor

are depicted

by integrating

perform

X-ray

(31),

reactions

of the allenylidene

were heated

for ring

in-

reactions

diallylmalonate

of catalyst

by 33 and 34. The sterically

lower

I28 h. A similar

in the RCM

diethyl

of 5 mol%

arene-ruthenium

crystal shows

signs of decomposition

for the CI$PCy;)(lMes)Ru(=C(H)Ph

are presented

energy

plex 34 (diethyl diallylmalonate plex 33 (diethyl diallylmalonate low catalytic

heat-

catalytic

complexes

2 h at 80 C. In order

strates,

com-

were monitored

I%elcctron

di(?-methylallyl)~iialonatc even

The

reactions

disappearance

temperatures.

di(?-methylallyl)malonate

solution

a

solvent.

in the ‘H NMR.

compared

Both

were found.

diene

and diethyl

of the RCM

tion and diene

0

(=C(H)Ph.‘7.“”

different

containing

deuterated

II x 1 0 0

7 t1

to elevated

33 and 34 as catalyst

Three

Illin Illin Inin lnlin h

at 80 C.” Even after 32 h of constant

has been observed

to Cl$PCyj)?Ru

diallyltosylamine appropriate

subjected robust

products

The role of complexes was investi,uated.x3

15 15 75 25 ?

33 after 64 h and for complex

stability

,AUD 34

spcctt-owopy.

ing no signs of decomposition creased

BY 33

CD~CI: CIl~(‘I~ c’I>gI~ (‘Il~c‘I~ d~-toluerle

out to be relatively

wcrc noticed

MEDIATEI)

33 34 33 34 33

33 and 34 were

turned

XII

MI, I A I HIAIS

29 29 30 30 31

“.Monitored

~OLIII~S

CI.OSING

207

Carbene Ancillary Ligand

sub-

rates after

substituted

com-

0%) compared to com4%)). The disappointingly reactions

obtained

for 33 and

34 could be attributed to the very similar metal-ligand bond distances in the solid state indicating a similar electronic environment at the metal center for both complexes.

208

JAFARPOUR

El. Carbon-Carbon Palladium methods

and Carbon-Nitrogen

catalyzed

lents with various

cross-coupling

nucleophiles

for the formation

ofC-C namely.

product

in the early

synthesis.

arylhalides

and

C-C

The

or arylhalides complexes. portant It has

shown

been

role in dictating phosphines

amines

that the supporting the efticiency

coupling

reactions

more

> C-l).

benetit

a number

of industrial

processes.’

N-heterocyclic

carbcnes

Nucleophilic

do not easily

cess of the ligand ~lsually affording considerable Herrmann ancillary formation’“’

cfl‘cct

alkenyl or nickel

mediated ~CCWSC

coupling the in-

of

science.““’

center

play

Bulky

a

“‘I

crucial

monodentate

have hecn the ligand ’I5 Although

do arylbromides fcedstock

of

arylchloride\ or aryliodides

would

economically

If’ ’Ix as ligands the metal

in organometallic

have reported

involving factors

arylbromides required

and the results

nucleophilic

from

reactions

with

have

the primary

center,

and as

advantage result

a

an ex-

is not required in order to prevent aggregation of the catalyst the bulk ~netal,“.‘7.1’.‘7~~“.1”‘.170 Imidazol-2-ylidenes exhibit ;I

stabilizing

ligands

“I “‘.““‘L

(ArB(OH)?)

palladium

and materials

system.““““”

than

acids

rc‘ac-

in natural

used

reagents

on the metal

Lose as chemical

dissociate

and co-workers

the stereoelectronic bulky

their

slowly

> C-Br

The Suzuki

In Kumada

interelrt

PX (X = P. N. 0 Ibr amination) methods.

~OCLIS

or nickel

synthesis

of the catalytic

our attention

of either

significant

ligands

(C-Cl

that they

amounts

arca, palladium

in organic

in all the above-mentioned

undergo

Grignard

has attracted

we

are boronic

by reacting

equiva-

and practical

is extensively

and

(Ar’X).“‘-“‘”

of catalytic related

or halide

effective

reactions.

triflates

as

is accomplished

or hidentate

In this review

and Kumada

in this reaction such

of this methodology

LISC

choice

bonds.x”~“’

suhstratcs

in the presence with

of arylhalides to be highly

1980s is very versatile

‘I7 J”’ In a closely

of arylhalidec

reactions

Suzuki

or pseudo-halides

bond formation

Bond Formation

have been shown

on two of these methods. tion developed

AND NOLAN

carbenc

from as

Su.alki

systems

and activated

the thermochemical ligation

activity

arylchlorides.“’

in the metal-mediated

supporting

(1Ytlr .c.~,~r.rr).“.“.’ “),‘70

cross-coupling C-C

ofcarbcnc In view ot

and C-N

studies J7. the activity

in these catalytic

processcs

bond of was

investigated.

VI SUZUKI

CROSS-COUPLING OF ARYLCHLORIDES WITH ARYLBORONIC ACIDS

The Suzuki reaction has proved extremely versatile and has found cxtcnsivt: use in natural product synthesis.“’ Arylboronic acids IArB(OH)?] are the usual substrates in this reaction together with arylhalides or triflates (Ar’X. X = halogen

a

Nucleophilic or 1riBate).

In our initial

3-chlorotoluene and CslC03 carbenes

are considerably

develop

salt. Under

in which

which

yield

(59%

to air Ltnd tnoisture

isolated

the carbene

ligand

be generated

conditions. ;I

using

significant

IMes

yield).

Since

than the corresponding

of the carbene

would

acid and

the carbene

and isolation

represents

IMes.HCI

resulted

WC sought

to

in .citl/ from the in the isolated

improvetnent

lie IMes in terms of both isolated

the nucleophi

of phenylboronic

of Pdz(dba)j,

preparation

the s;lme general

of96%,

atnount

in a modest

less stable

salts, to avoid

a protocol

playing

in the coupling

of catalytic

as a base was observed

imidazolium

yield

experiments

in the presence

209

Carbene Ancillary Ligand

over the procedure enyields and ease ofexeculion

(see Eq. (9)).“”

WOW,

Me

I> 0

Pdz(db& (1 5 moloo) IMes HCI 13 0 mol%l base (‘2 equivalents) dmxane. 80 C 15h

Cl

An investigation

of the base for the

frotn the salt IMes.HCI Other

inorganic

reaction ployed,

of coupling

the reaction

observed.“”

tion with functional donating

products. within

As illustrated

groups

ligand

substituted

and provided

It is a significant synthesis

and especially

the reactivity cross-coupling

in process

of the air stable reactions.

Suzuki

reaction

with

variety

of functional

to avoid

groups

tolerant

palladiun~(11) Ii&and

investigation

of the ligands

ol

by the catalytic

products

in excellent

cotnplex

in organic

we set out to examine

(Pd(OAc)l)

XV, the palladiutn exhibited

g or -withdr:twing)

for in .viru generation

yields.“”

altogether

the at-ylchlorides and arylboronic acids and the corresponding were formed in very good yields.“” An

reac-

were both tolerated

IMcs.HCI

(electron-donatin

Suzuki

of a variety acids. Electron-

to0 Therefore,

in Table

black

and arylboronic

the use of a glovebox

As illustrated

the ancillary

catalyzed

etn-

was

of palladium

the palladium

coupling

chemistry.

moderate

tricthylatnine

was exceptionally

substituents

XIII).

in longer

and afforded

base

IMes

(Table

and CsF resulted

and precipitation

XIV.

the cot-responding challenge

the organic

minutes

ligand

ofchoice

arylchloride

on the arylchlorides

andelectron-withdrawing

systetn

When

in Table

K$ZOj,

ofthe

IMes.HCI

of the carbene

was the reagent

KOAc,

consumption

ceased

the ancillary

.vitu generation

it7

that Cs$Oj

bases such as N+CO{.

times for complete

to low yields was

revealed

in the Suzuki (II) catalyzed

tolerance

toward

substituted coupling

of the carbene

;I on

products ligands

from their salts revealed that IMes.HCI is our best choice (Table XVI, entry I ); all other imidazolium salts investigated resulted in longer reaction times for complete

JAFARPOUR

210

AND NOLAN

TABLE Erwcr (‘AI

XIII

01’t3nsi OTL‘I HI: K,\ 1’1’ 01, I’d~(dha~;/lMe\.II~‘I

,{I Y/k11

It’r’ S[I/.l

KI (‘l~~,SS-(‘OlilJl.l~(;

OI- ~-(‘llI.OKOfOl.l~l~1\l~

1Vl-I.11 I’tiI,\1

RI ,\( IIONS I I~OI
Me

Pd2(db& (1.5 mol%) IMes.HCI (3 0 mol”b) mol”b) base (2 equivalents) d~oxane. 80 C 15h

consumption products.

of the arylchloride An interesting

I-ethyl-j-methyl

imidazolium

time (39 h). 75% of isolated the catalyst

bearing

and afforded

example

carbene

tnoderate

is, however.

hydrochloride

when

to low yields

of coupling

the commercially

available

was employed

yield

was obtained

ligand

is thermally

(Table

under

XVI.

entry

longer

reaction

4). This

stable as we have observed

mean5 in other

systems.“” Use of the imidazolium IMes

is a significant

methods. reaction

Furthermore, of arylchlorides

with

other

while

Pd(OAc)l

conditions Suzuki catalyst

salt IMes.HCI

improvement

existing

for the irl .situ generation Suzuki

cross-coupling

01‘

reaction

Pd(OAc)? can similarly affect the Suzuki cross-coupling with arylboronic acids. However, reactions performed

imidazolium

salts

was lhund

described

allowing

upon

above.

required

to be equally

longer as

So the current

times

and afforded

effective

as Pdl(dba)j

catalytic

system

coupling so far by employing arylchlorides precursors without the use of a glovebox.

lower

yields.

under the reaction

represents

as feedstock

the simplest and

handling

Nucleophilic

TAHI.E FIIKCTIONI\L CATALYZED CHI.0RIDF.S

GR~LW SLIZCIKI WITH

211

Carbene Ancillary Ligand XIV

To~cR,~uc~

01; Pdz(db:~~~/lMes.HCI

CROSS-COUPLING PHENYI.HOROYK

I&ACTIONS ACID

OF ARYI

I~~RIv,\TIwS

Pdn(db& (1 5 mol’%) IMes.HCl (3 0 mol%) cs2c03 (2 equl” ) dloxane. 80 C V

I .s I.5 I3 I3 I.5 I.5 I .5 I.5 I.5

H H

l-OMc 2.Me 3.OMe 4OMe H II H

VII CROSS-COUPLING OF ARYLCHLORIDES WITH ARYL GRIGNARD REAGENTS (KUMADA REACTION)

In the previous section the result of employing Pd(0) or Pd(I1) compounds and imidazolium salts as the catalyst system in the Suzuki cross-coupling reactions of arylchlorides and arylboronic acids was discussed.“” Considering that arylboronic acids and other organometallic reagents used in this type of C-C coupling arc generally made from the corresponding Grignard or lithium reagents9’ it would prove valuable to find a general method for Kumada coupling. Based on the success with IMes.HCl in Suzuki coupling of arylchlorides with arylboronic acids,“” we employed a similar protocol for Kumada coupling. In order to form free carbene IMes from its salt instead of using an external base (CslCO3 in Suzuki reactions), a slight excess of Grignard reagent was employed. Unfortunately, using IMes.HCl and Pd?(dba)i as the catalyst system in the reaction of 4-chlorotoluene with phenylmagnesiumbromide afforded a moderate yield (Table XVII, entry I).“’ Since the use of bulky ligands may improve catalytic performance in this C-C coupling procedure,“‘.“‘.y6.‘0~,‘~4,‘~~ the cmbene salt

212

JAFARPOUR

AND NOLAN

TABLE XV Pcl~OAc)~/IMe\.tlCI <‘A I’,\1 Y;/I:I) SLf/I KI ~l~OSS-C‘O~~lJl.l~~; Rt.,\c’l AC.II) DL:KIV,\ I I\I,S 01 Al<\II.ct~I ol~Inr;s\\,ilh ~IIl:NYI.I~OIU)\I(

;hJ + ,;$H)2Pd(OA& (2 5 molooj c IMes.HCl(Z 5 moloo) -T Cl

y

cs*co3 dloxane.

(2 equtv ) 80 C

ION‘,

xp, _xc x I/:1

Y EIllQ I 2 3 4 5 6 7 x 4 IO

X &MC &MC &MC J-MC J-co~ble J-MC i-NML!: 7.s-(Mc)J 7.5.( Me 12 ?.h-(Me)?

Y

‘Tim (11)

Isol;~led Yield (‘1~)

II 4.OMe ?-Me 3.OMe H H II H II H

2 2 2

YO x0 so

I0 II x 2 7 2 2

03 YY x5 Yx” Y-1 YX” ho”

IPr.HCI was employed in this reaction and afforded a 99% yield of isolated product (Table XVII, entry 2). The result is consistent with the stereoelectronic propcrtics of this family ofligandssJ7.“” The ligands are excellent donors and therefore facilitate the oxidative addition ofarylhalides. The steric bulk provided by the ortho position substituents on the imidazolyl aryl groups rnay serve to stabilize the active catalyst which we feel is a “LPd(Ar), ” intermediate. This intermediate may very well be stabilized by solvent or substrate binding to complete the square planar metal coordination. The role of the solvent was also investigated and the result showed that optimum yield is achieved by using dioxane as the co-solvent and heating the reaction mixture to 80’C. The reaction in THF/toluene and THF required a longer reaction time and lead to lower yields (Table XVII. entries 3 and 4).“’ A survey of catalytic cross-coupling of arylhalides with arylmagnesiumbromides using IPr.HCI is presented in Table XVIII. Reactions were faster for arylbromides and aryliodides than for arylchlorides (Table XVIII, entries 3, 8, and IO). As in similar coupling reactions, the significant challenge in practical Kumada reactions is the functional group tolerance.“‘.“h The halides bearing methoxy (Table XVIII, entries 4, 10-14) or hydroxy (Table XVIII, entries 8 and 9) groups react with Grignard reagents to form biaryl in excellent yields. When methyl 4-bromobenzoate was used, methyl 4-phenylbenzoate was isolated in 69%

Nucleophilic

213

Carbene Ancillary Ligand TABLE

XVI

Pd(OAc), (2.5 mot%) L-HCI ( 2 5 maloo) cs2co3 (2 equl” ) dsoxane. 80 C

E111ry

L.

Time (11)

TABLE or CHI.orwroL~wk

CK~~~-COIIPI.IUG

lISIX:K

V/\RIOI’S

Iwhlcd

Yield (% )

XVII wi i 14 PHENYI

hi,\(iUf’slI’MHRonIll)t:

CoNC)l~rIoNs Me I

MgBr

b,I; + ‘--,1

\ (-I-: /

Cl

Mry I 7 3 1 5 6 I

-

Pdn(db& (1 0 moloo) L HCI (4.0 mol%)

L

Solvent

Temp. ( C)

Time (h)

IMe IPr IPr IPr None IMes IPI

Et?O/THF Er?O/THF Tolucnc/THF THF DioxaneiTHF DioxaneiTHF DiowwTHF

-Is 4s x0 x0 x0 x0 x0

10 20 20 s 3 3 3

Isolaled Yield (56) 3s 97 IO 80 0 II 99

214

JAFARPOUR

AND NOLAN

TABLE XVIII

Ar-X + Ar’MgBr

w

Ar-Ar’+

MgBrX

Pd2(db& (1 mole,) IPr HCI (4 moloo) dloxane/THF 80 C

Enlr\i

,A-X

Time th)

Yield (% 1”

yield (Table XVIII, entry 7). even though more complicated byproducts were formed when the less reactive chloro analog was used. Although sterically hindered substrates are often problematic,““~‘“‘~‘“” the ortho-substituted 2-fluoro- or 2,4.6trimethylphenylmagnesiumbromides coupled with 4-chloroanisole without any difficulty. When ortho-substituents were present in arylchlorides. good yields were obtained by using a slight excess of Grignard reagent (I .8 equivalent instead of I .2 equivalent). However, the coupling of 2-chloro-rrz-xylene or 2-bromomesitylene with mesitylmagnesiumbromide failed because of steric congestion around both reactive centers. Homocoupling products of Grignard reagent were observed in all other reactions as minor products with the exception of mesitylmagnesiumbromide where no homocoupling was detected.lz3 While the mechanism remains to be elucidated, it seems apparent that at least diarylpalladium intermediates are involved in this reaction.“’ At some point the

Nucleophilic steric bulk of the ligand tion,

becomes

as IPr is a poorer

We have recently similar

high

observed

yields

an understanding carbene

more important than IMes

that using

in a shorter

time.

of the “active

ligand.

arylchlorides.

donor’”

arylbromides,

and an imidazolium

a Pd/L

ratio

This

in more of I/l

observation species”

presented

as the catalyst

affords

bearing

by simply

donor

effective

makes

above proves

and aryliodidcs

chloride

than its electron

but results

catalytic

The methodology

215

Carbene Ancillary Ligand

only

contribucouplings.

the products

in

sense in terms

ol

one nuclcophilic

effective

for unnctivated

employing

Pd(O) or Pd(Il)

precursor.

VIII AMINATION In the previous as part bond

sections

of’ a catalytic

arylamination Ii&and

rides.

a similar

an effort

precursors protocol

to select

imidazolium

are shown

in Table

XIX.

we were

bulky

Based

positive interested

imidazolium

on the success

in Suzuki”” effective

chlorides The

IMes.HCl coupling

the amination

TABLE ARIIUATION OI: ~KIII.OKOJOI

what have

was found

and IPr.HCI

reaction

H/

as anIn

of I .Sdiaryland the results

to be the most

IMII~A~~I.~~~I

CHl.Ol
Me Na

the

arylchlo-

of arylchlorides.

XIX

KNF: USING DIWI,KI.NI

effect

on catalytic

involving

salt, a number

used in ;I model

IPr.HCI

ligands 01‘ C-C

might

with

were

carbene

on the east

in examining

ligands

imidazolium

bulky

bulky

effect

and KumadatZ3

was used to perform

the most

substituted

that employing

has a major

Therefore, selected

reactions.

cillary

it was shown

system

formation.““.“3

use of judiciously

OF ARYLCHLORIDES

Pdn(db+ (1 mol%) L HCI 14 mol%l KO’Bu, dlaxane 1ooc

I 7

None ITol

3 3

0 <5

3 4 5

IXy” IMe\ IPr

3 3 3

II 32 9x

eff‘ective

216

JAFARPOUR

imidazolium

salt examined,

98% yield

(Table

A survey cyclic

XIX,

of catalytic

or acyclic

Table

XVIII.

chloride

4, 5. and

without

amines

(Table

illustrated

in high

difticulty. XX.

entry

primary

and secondary

catalyst

allows

Generally,

chloro

is provided

it initially

lignnd

in

deproto-

i/l .sit~ which

system

then

the HX formed

proves

general

and

XX.

reacted

with

various cyclic

yields.

amines

(Table

with

reacted highly

The generality

includ-

XX. entries

arylchlorides

01‘ 3-chlorotolucnc

of unhindered

alkylamines.

(Table

involvin

with

hindered

of the method

arylchlorides

with

i\

both acyclic

To the best of our knowlcdgc g arylbromides

no reported

XXI)

reacted

prove

with

temperature

the dctailcd

XXI.

smoothly baring

in process

remains

under

the halide

catalytic

system

Both

arylbromides

at room

temperature.

both chloro

and iodo (01

and iodo functionalitiec

entries

bc converted

advantage

mechanism

aryls

that bromo

(Table

can subsequently a significant

of the present was examined.

amines

involving

proceed

In order toexamine

and selecti\,ity

is the observation

functionality

and aryliodides

arylchlorides.

and aryliodidca

in these studies

at room

This could While

coupling

of arylbromides

substituents

converted

catalytic

Ortho-substituted

reaction

cl‘t’ect, the efficiency

interesting

bromo)

yields.

than those involving

and aryliodides Most

This

7) leads to lower

aminations

substituent

in a

this transthrmation.

conditions

for amination

product

and secondary

hasc to neutrali/.e

6, 7. and 9) and secondary

The

by the efficient

is two-fold:

in Table

arylchlorides

XX. cntrics

I I ) amines

amine

ligand

the free carbene

presented

unactivated

(Table

primary

as a strong

reaction.

by results

The less reactive ing primary

milder

to form

of the coupling

as shown

with

as the supporting

base KO’Bu

to Pd(O) and also scrvcs

in the course efficient

of the coupled

of arylhalides

usin g IPr.HCI

role of the added

nates the imidazolium coordinates

to the isolation

5).

cross-coupling

amineh

The

leading

entry

AND NOLAN

can be

3 and 3) and the remaining at more elevated

temperatures.

chemistry.

to hc clucidatcd,

it seems apparent

that

at least arylamidopalladium intermediates are involved in this reaction as prc‘~~.Ioo.Iol.loi.lfl~.Ill~r.I IO 115,11x It appears to us that both stcric and viously observed. electronic

effects

tron donor

propcrticx

combine

to mcdiatc

a secondary the carbene

effect may be provided by the hulk located at the ortho positions 01‘ aryl group. Results of structural studies in related platinum complexes

of the carbene

the coupling facilitate

process.

the activation

Initially,

the clcc-

01‘arylchlorides

and

of general lormulation L?PtMel (L = nucleophilic carbene) indicate that thcsc ortho positions are oriented directly toward the groups involved in the reductive elimination this

reductive

step. Stcric elimination

hindrance

imparted

step. At this time

by the ligands

w’ould

we feel the LzPdCl?

therefore may

very

favorwell

represent the resting state of the catalyst. We believe ;I combination of effects are at play: once the electron donor carbcne imparts enough electron density to the metal to enable it to perform the oxidative addition. the ligand stcrics subsequently stabiIiLe the reactive intermediates. The steric effects provided by ortho-substituents on

Nucleophilic

TABLE AMINATION

01, AKYL~HLOIIIIM

XX WITH

Pdn(dba)s. IPr HCI KO’EU d~oxane ArCl

Entry

+ HNR’R”

AFCI

217

Carbene Ancillary Ligand

HNR’R”

V~RIOIJS

*

AL4lNt.S”

Ar-NW?”

Ar-NR’R”

Yield

(% 1”

H-N 3 H-N

n

0

H,N-

“zN -0\ / H-N

vje \ / -(I> \--1 cI e

Me0

/ \ - -

NnO

93

the carbene aryl groups influence the efficiency of the catalytic transformation in a dramatic fashion. Our thermochemistry studies on ruthenium systems involving these carbenes”.“” show that ITol is the best electron donor (1Tol > IMes z IXy > IPr) while IPr is the most bulky ligand (IPr > IMes S=ZIXy > ITol). The catalytic activity of systems involving these various imidazolium salts follows the steric trend. When a Pd/L ratio of l/I is used the products are formed in similar high

218

JAFARPOUR AND NOLAN ‘I’AllLl2 XXI AhllUhl

ION OI AKYl.l~RoRlII)I.\ Pd*(dba)? IPr HCI KO’Bu. dloxane

ArCl + HNR’F”

Entry

yields

AC-X

but in a shorter

for generating In summary. (and

makes

bromides forming

arylchlorides methodology with

as well as arylbromidcs

both acyclic

primary

appears

excess ligand.

methodology

for the amination

has been developed.

precursor

the lirst

this ratio

Without

of a palladiun~(O)

the catalytic

Yield (% )”

optimum the resting

can not be reached.

and iodides)

provides

discussed,

intermediates.

and ef’ficicnt

use of ;I combination

chloride

Ar-NR’Fi

,\I--NR’R”

As previously

“Lz Pd(Ar)(X)” a general

*

HNR’R”

the active catalyst

state composition rides

time.

,411) lolNl)l~,sl’

which

complex proves

and aryliodides

report

of arylamination

and secondary

The

simple

of arylchlomethodology

and

an imidazolium

efi’ective

for unactivated

in high isolated involving

yields.

Thij

arylchlorides

alkylamines.

IX CONCLUSION This journey started where I‘undamental thermodynamic these data it became

most of our studies are initiated: from our interest in properties quantified by solution calorimetry. From

clear that nucleophilic

carbenes

(most

of them

anyway)

are

Nucleophilic better

donors

calorimetry

than the best donor allowed

phosphines.

us to put on paper

This

“feasible”

stability

from the steric protection

they differ electron

in the electronic donation

IPr are more

than

provided

requirements:

as possible. enough

The fact that IAd can effectively electron The

donation nucleophilic

They

reside

Much

remains

of ligand remains

is really

bond

carbene

metathesis

benefit

donation

fences.

from

provided

activation

yet

as much

by IMes

in coupling

OI

catalysis.

is a clue as to how much

this conversion.

are “phosphine-mimics” electronic

with these ligands. properties,

in both

reactions can be attributed to Both these catalytic processes

these processes

to mediate

end of the Tolman

to be explored

stereoelectronic

mediate

needed

carbenes

at the upper

C-Cl

by the

Developments

by the nucleophilic olefin

We feel the electron

to allow

scale provided

reactions.

olefin metathesis and palladium-mediated coupling the thermochemistry guiding us in the right direction. bcncfit

219

Carbene Ancillary Ligand

but they and

steric

With a rudimentary

we feel confident

much

arc much parameter

more. scales.

understanding

exciting

chemistry

to be explored.

REFEKENC‘I:S

(3) <‘oIlman. J. P.: Hegedus. L. S.: Norton. J. R.: Flnke. R. G. P/?wi/,/r.~ r,,u/ .~/~/J/;c~c~/;o/I.\of O/~ci,l,,ri.ir,fsifiorl Mrtrrl CIw~~~i.vt~.\:2nd cd.: University Science: Mill Valley, CA. 19X7. (4) Kuba\. G. J. Aw. C/w/u. Rr.v. 1988, 21. 120. (5) Gowale/.. A. A.: Muketjee, S. L.; Chou. S.-J.: Zhan,. (7 K.: HoR, C. D. J. ./. /I,,/. Chrur. Sot. 1988, 110, 4419. (6) Nguyen. S. T.; Grubba, R. H.: Ziller. J. W. J. Am. Chrr. SK. 1993, 11.5, 9858. (7) Fu. C. C.: Nguyen, S. T.: Gruhbs. R. H. J. Am. C/wrr. Sot,. 1993, //S. 9X.56. (X) Ardurngo. A. J.. III: Rasika Dia. H. V.: Hxlow. R. L.: Kline, M. ./. Auz. Cheul. Sot. 1992, 111. 55.10. (9) Wan/-lick. H.-W. Ayyn. Cl~wr.. ht. Ed. Eq/. 1962, 1. 75. ( IO) Lqpert. M. E J. Or,~trrmwt. Clwm. 1988, 35X, 185. (I I ) Arduengo. A. J.. 111; Krafczyk, R. C/w/n. Z. 1998, .?2. 6. t 12) Wanzlick. H.-W.: Schikora, E. Angew Clrrm. 1960, 72, 494. ( 13) Wanalick. H.-W.: Schikol-a, E. Chr,u. &I: 1961, Y4, 3389. ( 14) Wawlick, H.-W.; Kleiner. H.-J. Ayew, Chrrn. 1961, 7.1. 493. (1% Wanzlick. H.-W.; Esser. F.: Kleinel-. H.-J. Clrr~u. Rr,: 1963, Y6, 1208. ( 16) Warvlick. H.-W.; Kleiner, H.-J. Clwr,~. He,: 1963, Y6. 3024. (17) Wanzlick. H.-W.: Ahrens. H. Clwu. Ret: 1964, Y7, 2347. ( IX) Wanzlick. H.-W.; Konig. B. Cluwr. Brr: 1964, Y7, 35 13. t 19) Wanrlick. H.-W.; Lachmann. B.: Schikora. E. Chwr. Rer: 1965, YK. 3 170.

220

JAFARPOUR

AND

NOLAN

Nucleophilic

Carbene

Ancillary

221

Ligand

159) (iruhhs. R. H.: Millcl-, S. J.: Fu, G. C. ilc,c,. C/~/II. Km. 1095, IX, 416. (60) Schwb. P.: Frnncc, M. B.: Zillcr. J. U’.: Gruhhs, R. H. A/~,qcw. C‘lw~r.. I/r/. IG/. /+I;;/. 19Y5, .U. 20.39. (61) Schwab. P.: Grubha. R. H.; Ziller. J. W. ./. Am. Chem. .Sw. 1996, l/h’. 100. (621 Dia/. E. L.: Nguyen, S. T.: Grubhs. R. H. ./. .4w. Clwm. Sor,. 1997. I IO. 3887 (md the referews cited theI-tin).

hr,y/. 19Y6. -1s. IOU

1999, I?/.

7!, I.

(7 I) W~~hamp. T.: Kohl. K. J.: Hicrinper. W.: Glrich. D.: Herrmann, W. ,I. A~r,~cw. C/I~,UI.. /,I/. tri. hr,y/. 1YYY. .3x. 2116. (72) Scholl. M.: Trnka. T. M.: Mot-gan. J. P.: GrLlbbs. R. H. 7?/w/wt/1r~1 Lcr/. 1999, 40. 2217 173) Scholl. M.: I)ine. S.; Lee. C. W.: Gnlhh\. R. H. O~:qc~ric Lcrro,:! 1999, 1. 95.1. (7-1) Fiir\tner. A.: Picqwt. M.: Brunea~l. C.: Di~neul’. P. H. C/rrw. C~wmro~. IYYX, Ii Iti. (75 1 l:iit-\tncr. ,A.: Ackemunn. L. C‘lwm C‘om~r~~~~.199’). 95. (70) Harlow. K. J.: Hill. A. F.: Wilton-El). J. D. E. T. ./. C’lrrm. .%Ic~../)cl/ro~~ 7,.or1.,. 1999, 2X5. (77) t:iir\tnw. A.: Hill. A. F.: Lirblc. M.: Wilton-Ely, J. I). E. T. C‘iwm. C‘omrrm. lY99. 601. (7x1 Jal’xpour. L.: Hwn g, J.; Stevens. E. D.: Nolm. S. I’. O,~cl/~o/lrc/ci//i~,\ 1999, /S. 3760. t70) Picquet, M.: Bruneau. C.: Dixncuf. P. H. Clwrr. (‘m~mror. 1998, 271’). I 80) Hafncr. A.: Muhlehach. A.; van der S&anr. P A. A~gcw. C‘hcm.. Ifrr. /xl. /qq/. IYY7, 36, 112 l (XI 1 Jnf:trpwr. L.: Schm/. H.-J.: Stewn~. E. 0.: Nolan. S. P. ()~~~~~~ror~~~~~~~//;~~.~ 1999, IX, 53 I h. (X2) Fiil-Qncr. A.: Hill. A. F.: Jalarpour. L.: Stevens. E. I).: I,icbl. M.: Nolan. S. P.: Wilt~,n-Ely, J. D. E. T. 1Y9Y. manuwript in prcpnmtion.

tX6) Bill-ie/.

(X9) (90) (9 I 1 (92) (Yi) (Y-l) (YS) (c)6)

B.: Burn\,

I, I).; Hill. A. F.: White.

A. J. P.: Willinnl\.

D. .I.; Wilton-El?.

J. D. E. ‘I‘.

19x2: Vol. x. tiech. R. F. I’ollr~rlilr~r~ Ker,,yc,rlr.\ i/r O,;qo~ri<. .~~,~//~c,tj\; Academic Prrs\: New York. 1985. Tat!ji. J. /‘~//trt/iw~r Retrgc~u/.c trrxl Cotol~w; Wiley: Chichcstel-. 1995. T\uJi, J. .Swt/rr.si.s 1990, 7.70. Miaura, N.: Sumhi. A. C/wm /+I: 1995, 9.i. 2457. Ilnmann. B.C.: Hartwig. J. F. J. Am. C/wm .SOC~.1998, 120. 73hY. Recta. M. T.: Lohmer, G.: Schwickardi, R. Ar~grn: (‘lwm.. /rr/. ,%/. &y/. 1998, .37, 3X 1. Litthe. A. F.: Fu, G. C. .I. Or;q. Clrorr. 1Y9Y. 64. 10. Zhnng. C.: Huanf. J.: Trudell. M. I..; Nolan. S. P. J. 0,-i’. C‘lwm. lYYY, 6-i. 3x01.

222

JAFARPOUR

AND

NOLAN

ADVANCES

IN ORGANOMETALLIC

CHEMISTRY,

VOL. 46

O rganometallic Chemistry of Transition Metal Porphyrin Complexes PENELOPE

J. BROTHERS”

Department of Chemrstry. The University of Auckland, Private Bag 92019. Auckland, New Zealand I.

II.

Ill.

.......................... Introtluction .A. Bachgt-“L”ld ....................... B. Scope (‘. The Porphyril> a\ ;I Supportin, 0 Ijgand in Organotndtic (I‘hmli\tr~ The Early Tramition Mrtala tGrtrup\ i m d 4) ~mcl Lanthnnide~ A. o\Cl-\.ieM’ ................... ............ B. Scantlium. Yttrium and Lutrtitlnl. c Titamum......................... Il. Zirconitm~ and Hal’nium .................. The MiddleT~an~ition Elements tG~.oups 5. 6. and 71 ........ A. Owrvicw ..................... 1 % Tmralum. ...................... c‘. Clvomium. Motyhdenum. and Tungsten .......... I).

IV.

V.

VI.

Man~~lncsc

.......................

Iron. ......................... .A. Overvieti ..................... B. Ironn-Bonded Alhyl and Al-y1 Conlptexc~. ....... c’. II-011 Porphyt-in Cat-hew Conlplexe~ ............. II. Oxidation Proccsw Catalyoxl hy Iron Porphyrin\ ........ .................... Kuthcnium and Omiwn A. Overview ......................... IS. Kuthcnium and Owiiu~n n-Bonded AlLyI and AqI Co~nplexe~ ......... (‘. Cornptexc~ with ,~~Bo~ded Lignnd\. .......... II. Hydride and Dillydro~ell (‘olllplexe\ ............................ (‘dxdt. Overview Cotxdt rr-Bondetl Ally1 and Aryl Cmptexe\. The Sewch ior Cobalt Porphyl-in tiythxle Complex\ Cohatt Porphyrins it\ Catalysts l’or the Polynieri/ntiol1 of At!dnc\ Reaction\ of Cotxtlt(lll) Pal-phyriw \vith Athcnc\ and Athytw. d~uni and Iridium Obclniew Khodium and Iridium rr-Biontled Athyt and Aryl Complexr~. Keactions of the Rhodium(ll) Pot-phyrin Dinw and Rl~od~urn(lll) Porphyrin Hydt-idc. 1). C-H Activation by Khodiunl Porphyrin\. 17. Activation ol’ CO and Iwcyanidc hy Rhodium Porphyt-in\

... ...

223 All rights

Copyright c 2001 by Academic Press. of reproduction in any form reserved. 00653055/01 S35.00

224

PENELOPE

J. BROTHERS

F. G.

Reactions of Rh(lll) and Rh(l) Pal-phyrins bith Otpanic Suhatratrh Rhodium Porphyrin Carhcnc Complexe\ and the (‘yclop~opnilatioll 01‘Alkene Catalyd by Rhodium Porphyrim H. Hetcrohirnetallic Rhodlurn Porphyrin ~o~nplcxc~ The Late Transition Metals (Group\ IO. I I, ;mcI 12) A. OVCI-\ icu 13. Nichcl. C. Palladiun~ I>. zinc Non-Cowlcnt Interaction hctwecn Mctalloporphyrltl?, and Organic Molecules. Rcl’crencc\

VIII.

1X.

3M ,307 .3ou 310 .3IO ?I0 il I 117 312 .3 I 1

I INTRODUCTION A. Background The systematic ture, and

chemistry

reactivity, 1970s.‘.

porphyrin

This

growth

species

phistication

in biology,

and availability

istry

firmly

despite

metal-carbon

o-bonds.

dichlorocarbcnc

cycle

carbene,

that there was much

as a supporting

induced

alkene,

migrations

ligand

organometallic

the two the report

in 1977

alkyne,

and hydride

to be learned fragments

by unanticipated into a rhodium

rather

of an iron complexes,’

porphyrin examples it became

For example.

the coordinated

uncon-

containing

f’rom the use of the porphyrin between

the

chen-

1980s by further

chemistry.

by

in so-

During

compounds

the early

pyrrole nitrogen atom was shown to be relevant in cytochrome P450.” Classical organometallic in porphyrin complexes this, the insertion of’C0

areas remained

during

in organometallic

of organic

increase

techniques.

metal

1960s

role played

and spectroscopic

of metalloporphyrin

with

I’ followed

by the simultaneous

struc-

the

of transition

although report

However,

complex..

of mctalloporphyrin apparent

and scope

established,

encompassing rate during

in large part by the central

and facilitated

the occasional

complexes,

at an astonishing

of structural

the importance

became

grew

was spurred

same period, nected,

of metalloporphyrin

and spectroscopy,

macrothe redox-

metal

and a

to the function of iron porphyrins reactions were shown to proceed

radical reactions, and one example of hydride bond to form a f’ormyl complex.

was a process hitherto not observed in organometallic chemistry. The publication. in 19X6, 1987, and 1988, of three reviews f’ocusing on the organometallic chemistry of transition metal porphyrin complexes was an indication that this area had become Over

firmly

established.“.7.x

a decade

on, this area is now beginning

to reach

the early new developments subjected to intensive research New areas have been opened up. for example, organometallic

maturity,

with

some

and now consolidated. complexes of group

of 3

Transition Metal Porphyrin Complexes

225

and 4 metals which were unknown at the time of the earlier reviews. Aspects of organometallic chemistry which have become important in the last decade such as C-H bond activation. the relationship between metal-hydride and dihydrogen complexes, and supramolecular interactions have resulted in parallel developments in porphyrin complexes. The use of porphyrin complexes in catalytic organometallit processes has begun to be developed, as in the cobalt porphyrin-catalyzed alkene polymerization and the shape selective catalysis of alkene cyclopropanation by rhodium porphyrins. This review essentially comprises a survey of the developments in the organometallic chemistry of porphyrin complexes over the last decade. continuing on from the three reviews published during 19X6-1 988. Literature since the mid- 1980s has been surveyed. and work reported prior to this will be touched on primarily to put the more recent developments into context and will not be described in depth. A new multivolume set encompassing the entire range of porphyrin chemistry has been recently published, and this contains a chapter on organometallic porphyrin chemistry.”

B. Scope The broadest description of an organometallic porphyrin complex is one which contains both a porphyrin macrocycle and a metal carbon bond. A useful classification of the types of organometallic porphyrin complexes has been described by Richter-Add0 in a recent paper,“’ and his system is summarized here (Fig. I ). Type A complexes contain one or two metal-carbon single or multiple bonds. This class comprises the majority of the organometallic porphyrin complexes which contain a-alkyl, o-aryl, or carbene ligands. Both tive-coordination and sixcoordination is possible. with typical formulae as follows: M(Por)(R). M(Por)(R)(L). M(Por)(R)z, M(Por)(CR:), M(Por)(CRz)(L), M(Por)(CRz)?. Notably absent from this category is an example of a metalloporphyrin carbyne complex. Type B complexescontainrr-ligands. including $alkene, $-alkyne, $cyclopentadienyl.

PENELOPE J. BROTHERS

226 and related

ligands.

The

newest

the first metalloporphyrin /.L-M,N

groups

in which

bonds

fragment. aryl

Ihe alkyl

associated

with

structure

showing

on the periphery

tain a metal coordinated

in 1999.

involve

is

bridging

the coordinated

metal

to one ol‘the

attempts

and this review Types

most reported

use of inetalloporphyrin

the growing

number

interest

in supramoleculnr

lead to an increase

of types D anti E are largely beyond the scope ol‘this review. The exceptions of rypc E compleucs

as “inor~anometnllic

described

metal~he~croaloni

bonds

or carbene

Metalloporphyrin

pies from

ligand.

this category,

Defining

in which

tions

However, in modern

the widely

the central

l’ronts. Metal

moiety

complexes

i\ isolobal

and stannylene

complexes

by the remarkable metal imido

isolobal.

biological

has link\

alkenc

criterion

has

compounds

and rcac-

may involve

intermediates

A good example

by high-valent transformations

to organometallic

(M=NR).

As a result.

are exan-

in the rc\ieu. metal and

interaction.

catalyzed

an alkyl

the coordinated

by organometallic reactions

con-

contain

with

of these are discussed

thal many

chemistry

This chemistry

oxo (M=O).

ments are formally

However.

a subset of the area some-

in which

a bond between

role played means

oxidation

spurred

P450.‘”

stannyl

states with a metal-carbon

studied

oxo species. tochrome

“”

the heteroatom

containing

chemistry

or even transition

compri\c

types.

1-u iew has not been easy. and the central

been to Ihcus on compounds carbon.

which chemistry

and some examples

the scope ol’the

ofthese

in the

chemistry

should

times

ol‘exa~~~plcs

examples

smaller

plexcs

are some examples

in the number

cons

;I metal-carbon

through

by ;I much

blocks

an

rings’ ’ or to

rypch or organometallic

in the late 1990s. However.

as building

E

metal

of examples

to cover all the important

D and E are represented

moieties

pyrrole

important

Type

of a second

A number

of the porphyrin

porphyrin

con~plcxcs,

porphyrin

of the porphyrin.

to the periphery

these categories.

to the porphyrin.

sites for coordination

the mosl

ofcxamples,

belween

not coordinated

possible

(T bond. Types A. B, and C comprise from

reported

C complexes

bridges

the metal

It can be 7r-coordinated

substituenl

group

Type

nitrogen

these complexes. is a composite

in this category.

complex.

atom. The M-N bond may or may not be retained in bond, with the mctalType D complexes contain ;I me(al-metal

and one porphyrin carbon

example

r-ally1

mediated

chemistry

and melal carbene epoxidation

of Ihis is

metatloporphyin by cy-

on several

(M=CR?)

frag-

and cy~lopropa~~ntit,n

reactions mediated by metalloporphyrin oxo and carbene complexes. respectively. are closely related reactions, yet while the latler is an organometallic process. the former is not. On ;I more subtle level. the reactions involving metal oxo \pccies thcmsclves alkenc action

may or may not meet the criterion

cpoxidation

process.

for

t’or a met&carbon

example. ih proposed

by

interaction.

SOIIK 10 involve

The inter-

of the alhcnc substrate with the metal contcr prior to. or concerted with, 13 Ii oxygen atom transfer, in which case there is 21direct metal-carbon interaction. Other rcscarchcrs invoke a direct transfer ofoxygcn to the substrate without intcraction of the alkene with the metal. Overall. mc~alloporphyri~~ oxo chemistry and related developments in imido chemistry by themselves carry sufficient weight

. 227

Transitton Metal Porphyrin Complexes that they will

not be covered

ot’mechanistic

studies

For the purposes porphyrin

ofthis

complexes bonds.

review

whet-e

for a metal-carbon covalent

and non-covalent

porphyrin

complexes area where

boundary

between

carbonyl

complexes

Metalloporphyrin significant, usually tance

defining

occupied

by O2 in hetnoglobin

in biology.

criterion,

Although

much

of the work

on structure,

spectroscopic

and has liltlc

direct

ligands

isoelectronic

(CNR).

Porphyrin

of attention,

with cotnplexes from

This ligand

NO ’ is isoelectronic

~hc CN

. CNR.

One

also enjoys

dihydrogcn

complexes.

plcxes

key roles

play

of dihydrogcn important

The development istry of main group metals.

complexes

in some

data

family

ol

and isocyanidcs

have received

a recent burst

the role of NO in biological org~tnometallic

CO itself.

chemistry

complexes

when

containing

there is rotnething

chemistry. will

bonds.

be treated

involving

relationship

in the review.

are metalloporphyrin

organometnllic

reactions

and their

bond

has focused

A further

are CN

be considered that

tnct&carbon As in classical

complexes

advance

will only

impor-

and thertnodynamic

role in classical

of organometallic

ot‘ porphyrin

they do not contain

about

CO. As with

are also very

of CO in the site

complexes

bonds

the NO ligand

a special with

and NO ligands

in the context

lamily

containing

ligand

chemistry.

M-C

metal

chemistry.

is of enortnous

studies.

new understanding

systems.

though

form

in the

meet the metal-carbon

carbonyl

kinetic

arises

Tntnsition

coordination

tnyoglobin

10 org>mometallic

CO which

is difficult

carbonyl

clearly

porphyrin

properties,

because

to be learned

on iron

relevance

arising

and

these complexes

involving

in the review.

of organomctallic

where

to

ofsupratnolecular

chemistry.

an axial

containing

for iron porphyrins

evidence

be litnited

set of examples

of this review

and coordination

one of the cornerstones

cotnplexes

particularly

not. however.

as the last section

the scope

organometallic

only those

or spectroscopic

will

and a small

be included

form

to include

has seen the rise in importance

interactions,

will

structural

interaction

on the basis

may be part of the process.

has been refined

is direct

This

The last decade

it has been suggested

interactions

the criterion

there

interaction.

chetnistry Another

here, even where

that metal-carbon

chemistry,

porphyrins, to metal

even

hydride hydride

and com-

and the discovery

hydrides

has been

an

in the last decade. of both the coordination chetnistry and ot-ganolnetallic chenporphyrin complexes has been slower than that ofthe transilion

As a generalization,

and II i\ well established

the chemistry

of the middle

elements

(Al, Ca, In, Cc. Sn) with that ofthe

from

lightest

groups

I3

and heaviest

elements (B, TI, Si. Pb) less well known. If’ Advances in the coordination of the group IS clctnents (excluding nitrogen) are more recent. and porphyrin complcxcs containing elements phyrins,

group I6 or I7 elements are as yet unknown. A feature of main group is the coordination 01’ non-metals (boron. silicon, phosphorus) to porwith

sotnc of these (for cxamplc.

years. “‘I’ Organometallic main group companion review article.“’

boron)

porphyrin

reported complexes

only within

the last few

will be discussed

in ;I

228

PENELOPE J. BROTHERS

C. The Porphyrin as a Supporting The

porphyrin

planar

macrocycle

arrangement,

metal

coordinated

nation

numbers

ligand),

with

provides

I’our nitrogen

to a porphyrin

arc usually

pyramidal

observed.

geometry

the axial

arrangement

of the 5th and 6th ligands

sition

is common.

rare and observed

metals.”

the classic tion,

ligand

is by far the most common.

it is relatively

chemistry tation

insertion,

above

the plane

One

be strongly

01‘ the por-

the early

tran-

in many

reductive

of the great ligand

oi

climinaadvantages

in organometallic

gcometry.

inhibited

the NJ

the twos

is not precluded.

addition.

over coordination

might

from

sites is important

interactionx.

of‘control

that some these processes

(one additional

involving

as the supporting

for a coordi-

complexes

and below

like oxidative

and agostic

higher

the ci.s geometry

for complexes

in a square numbers

is displaced

For six-coordinate

largely

macrocycle

is the high degree

the metal

Although

processes

the porphyrin

ligands

For five-coordination

of c.i.\ coordination

The availability

organometallic

migratory

of using

donor

3, 5. or 6, although

in which

plane toward phyrin

Chemistry

a hole size close to 2.0 W. Coordination

are occasionally

square

Ligand in Organometallic

and the cxpec-

by the enforced

fr-~s

geometry. A f’urther

advantage

tion enviromnent

is that the 24atom

ofthe

central

element

on the periphery

of the porphyrin

tuning

and electronic

the stcric

core and hence the immediate can be maintained

macrocycle propcrtics

allows

intact, a high

of’ the ligand.

long time been used to great advantage

in the coordination

complexes.

begun

but has only

and understanding

more recently

the chemistry

tural variations

within

saddle-shaped,

or ruffled

the importance

of X-ray

relatively terized,

few organometallic

been

porphyrin

included

ot‘ physical

chemistry

porphyrin

in organomctallic

with

in

has for a

of porphyrin

complexes.

complexes

with

the exception

Struc-

fully

arrangements.

planar. ” Given

chemistry

in general,

have been structurally

true last time this area was rcvicwcd.

data tar organomctallic

in this review.

of control

property

core are possible.

amon g the common

distortions

and this was cspeciully

compilations

porphyrin

crystallography

substitution

to be used as a tool for manipulating

of organometallic

the ?4-atom

degree

This

coordina-

while

porphyrin of X-ray

complexes data.

charac-

Exhaustive have not

Ihr which

there

are now sufficient examples to warrant the inclusion of’ tables collecting selected data for structurally characterized olganomctallic porphyrin complexes. Simple sketches. using an oval shape to represent the porphyrin Ii&and. are used in the schemes and equations. However. within each section a represcntativc group of Struccomplctc structures are shown. usin g examples taken from the Cambridge tural Database. These arc also llseful for illustrating the effect of substitution on the porphyrin A particular

periphery and distortions of the porphyrin ligands. f’caturc of transition metal porphyrin chemistry is that the energies

of the metal tl orbitals and the frontier orbital> of’ the porphyrin ligmd arc often quite close, with the result that the redox chemistry of the porphyrin ligand and the

229

Transition Metal Porphyrin Complexes TABLE

Ahhreviatiorzsforporpllyrin

I

dianims

PotOEP

Porphyrill

dianioll.

unq7ecitied

TPP TTP OETPP TAP T/ICF~PP l’/lcIPP TMP TTEP TTiPP TXP

5. IO. I .5.2O-Tet~-~phcnyIpol’phyrit~ 5. IO, I .5.2O-Tetra-/~~tolylporphqrill 2.3.7.8. I?. Ii, 17. I tl-Cktxthyl-5. IO. I ~.2O-lerraplirnylt~~~rpt~yl-in 5. IO, I5,?O-Tetr~-p-mctl~o~yt~h~~~ylporpt~yri~~ 5. IO. I S,2O-‘~~~ra-~~-trii~t~~~ro~~~~~l~~~lpl~~~~ylt~~~rt~h~ri~~ 5. IO. I ~,20-Tcrra-/~-~tllorophenylporphyt-ii~ 5. IO. tS,2O-Tctra~ncai1ylt~~~rpl~yrin 5. IO. I5.20.Ttwaki\( I .3.5-~riett~ytphet~yt )porphyt-it> 5. IO. I5.?0-Terrahis( I .3,~-~rii~ol~t-opylpt~~~~yl)p~~rph~ rite 5. IO.I~.2O-~fe~~~xylylt~~~rphqri~i

2.3.7.X,l2.13.17.18-Octaethylpo~-~~h~~i~~

Abbreviations for anions of tetrapyrrole macrocycle~ Phthatocyanmr (dianion) 7.7,I1.t7-Tetrartt~yl-.~,6.I3. I (,~t~tt-~~nlc~l~ylp~~~plly~~t~~(diarlioll) 1.3,7.X.12.13.1 7.tX-Ocra~tl~ylco~-rot~ (II-ialiiwi) Octaethyltctraa~npot-ph~I-in (dimion)

PC EtioPc OE( C) ETA I’

coordinated

metal becomeentwined.

on the porphyrin electron

ligand

transfer

(kinetic

(thermodynamic employed

porphyrin

ligands

result

ligands

in different ligands

porphyrin

porphyrins

will

Porphyrin troscopic

by altering effect

and

the ultimate simple

are the dianions The

redox

potentials,

be defined

complexes. tools

particularly sorbs strongly

favored

suited

substitution

are given

macrocycle,

in the visible

in Table

being

physical

and

reduced

The commonly I. The numbering ofthe

two most

in Fig. 2. Less common

to the usual

chemists,

structural

and spec-

have characteristics

The

and near UV regions.

in the electronic absorption spectrum electronic environment. The aromatic

(TPP)

of the two

in the text.

amenable methods.

processes commonly

typically

and sketches

and H2TPP. are shown

by organometallic

to certain

most

patterns

with OEP complexes

as they arc encountered besides

of redox

the two

than their TPP counterparts.

of the porphyrin HlOEP

product

substitution

the site of initial

of tetraphenylporphyrin

and their abbreviations

ligands,

peripheral

on both

example,

complementary

L’(I. 200 mV more negative

for the periphery

common

Fine tuning a dramatic

As a very

(OEP).

used porphyrin system

control)

control).

octaethylporphyrin ut potentials

can have

porphyrin

and perturbations

can give useful information ring current associated with

ligand

that are itself

ab-

of the bands about the local the macrocycle

has an effect on the NMR chemical marked upfield shifts in diamagnetic

shift of axial ligands. which us~~ally exhibit complexes. In paramagnetic complexes, anu-

lysis

the porphryin

useful

of the chemical information

shifts about

of both

the location

of unpaired

and the axial spin

density.

ligands

can give

Six-coordinate

230

PENELOPE J. BROTHERS

17

15

Porphine numbering

13

Tetraphenylporphyrin

Octaethylporphynn

Octaethyltetraazaporphyrln

Etioporphycene

core and system

Phthalocyanlne

nc;.

porphyrin play

complexes

idealized

be identified

CH? protons

with

arc observed

paramagnetic

become

axial

different

spectrum.

dis-

cotnplexcs This can whet-c the

and display

;I

on the peripheral

environtnents

(assum-

time scale) and two sets 01

EPR spectroscopy

and g values can bc used to detertnine to the synthesis

ligands

ligands.

diastereotopic

is slow on the NMR

in the ‘H NMR

axial

of OEP complexes,

or-t/w and /nrttr protons

on the metal or the porphyrin

approaches

two different spectra

groups the

Inacl-ocycle\

to C;, in five-coordinate

at-e in chetnicnlly

rings

complexes.

spin is located General

Similarly,

wok

and two equivalent

reduce5

containing ethyl

in TPPcotnplexes of the phenyl

resonances

tct”“p>

in the ‘H NMR

A B pattern.

groups

ing rotation

This

complexes clearly

and

/~~tr/t.cgeometry

of the peripheral

characteristic phenyl

I’or[~I1)nn

DJ,, symmetry.

and in six-coordinate often

2.

Octaethylcorrole

is useful

whether

fot

unpaired

ring.

of organornctallic

porphyrin

complexes

have been described well in the original three review articles. By far the bulk of the chemistry has been reported for the groups 8 (Fe. Ru, OS) and 9 (Co. Rh, II-) elements. The organotnetallic chemistry of iron and cobalt has been established for the longest time, and n-alkyl complexes are generally fortned using one oftwo methods: reagent.

a metal(II1) or a metal(I)

halide anion

M(Por)X M(Por)

with an alkyl or aryl Grignard or lithium with an alkyl or aryl halide. Although these

methods are also useful for rhodiutn, the major developments in the organometallic chemistry of ruthenium, osmium, rhodium, and iridium complexes have paralleled the preparation and exploration of the chetnistry of the M(II) dimers [ M(Por)]?. The corresponding M O and W dimers are also useful in this context. The structural

231

Transition Metal Porphyrin Complexes and spectroscopic

features

and has been reviewed Organometallic cycles

complexes

closely

related

phthalocyanines. nmples.

the discussion

containing

in its own right.

molecules,

an area which

suffers

within

is destined

are included

porphyrin

from

to become

somewhat

this approach

pedcsto organ-

comprises

metalloporphyrins more

but

in Fig. 2.

and the big differences

last section

between

ex-

where

chemistry.

are shown

being

covered. The

of macro-

are the best known

the same group,

user-friendly.

interactions

of suplamolecular

variety

tetraazaporphyrinx,

The four macrocycles

of the chemistry

is the most

on non-covalent

a wide

with the relevnnt

approach

scope

discussion growth

or contrast

even of elements

of the review

contain

porphycenes,

:md porphyrinogens

descriptive

the huge

in the chemistry

story

the first four of these macrocycles

comparison

A group-by-group

zation

which

corroles.

will not be comprehensive.

but given

is an interesting

are known

to porphyrins:

tetraazaannulencs.

Examples

there is ;I useful

trian.

of these dimers

recently.”

;I short

and organic

signilicant

with

the current

chemistry.

II THE

EARLY

TRANSITION AND

METALS

(GROUPS

3 AND 4)

LANTHANIDES

A. Overview One class of compounds lit porphyrin

complexes

which

simply

were reviewed

did not feature

containing

theearly

transition

facilitated

progress

in this area W;IS the development

to the alkali

metal

solvcnt).‘3.” porphyrin

These halides

for the strongly purification

could

polar

Mz(Por)L,,

(M

simple

or ;icidic required

macrocycle,

tion elements.

These advances

lit chemistry

of the groups

salt elimination solvents.

in synthetic

of reliable Na.

K:

methods

routes

trunsition

metal the need

and chromatographic for insertion

not suit the oxophilic

methods

3. 4. and 5 elements

greatly

synthetic

This eliminated

high temperatures, would

complexes which

L = coordinating

to the early

routes.

in conventional and which

porphyrin

breakthrough

= Li.

then bc used ;IS precursors

through

commonly

into the porphyrin

metals.5.7.x An important

complexes

the last time organometal-

were organometallic

have allowed scandium,

of metals early transi-

the organometal-

titanium.

zirconium,

hafnium, and tantalum to flourish. resulting in ;I variety of complexes with unprecedented ligand types. stoichiometries, and structures. Recent developments in the chemistry ofearly transition metal porphyrin compounds were reviewed in 1995.” Some

of the key differences

metal

counterparts

highest

oxidation

between

are the tendency states,

the relatively

the early

transition

of the elements large

to form

metals

and their

compounds

size of the elements,

later

in theil

and the wide1

232

PENELOPE J. BROTHERS

range

of coordination

numbers

to 8 are encountered 5, and 6 commonly displacements

observed

are often

of the elements. coordination quite

commonly

structural which

observed.

contains

bridging which

two

and hafnium

dichalcogenide

complexes

contain

two bridging

of’ the early

metals

chemistry.

two cyclopentadienyl

lignnds.

exert a considerable

dium.

yttrium

and lutetium,

Representative

and 4 metals terized

complexes

B. Scandium,

(M = Zr. Hf:

such

between

on other ligands discussed

units. chemistry

as alkene

poly-

a porphyrin

ligand

and

a 2-

charge

and

fhrmal

in the same molecule.

below

lanthanide

Several

have bis(cyclopentadienyl) quite

detailed

comparisons.

here. porphyrin

types of porphyrin

in Table

the

E = S. Se$”

to the organometallic

in applications

in Fig. 3 and selected

are given

of’

Zr(TPP)(OAc)22i

of’ the porphyrin,

complexes

and they will be considered

structural

are shown

face

of’tris-Innumber

a

each pair of’metalloporphyrin

will not bc repeated

To date. the only organomctallic contain

8 including

in some cases have drawn

these discussions

in a variety ‘.“’ and

in that they both contribute

complexes

and authors

c,i.\ arc

M(Por)2.2K.21J and the very unusual

can bc drawn

steric influence

of the metalloporphyrin counterparts,

fcaturc

size

complexes.

on the same

are central

and

Parallels

the larger

in six-coordinate

[M(TPP)(E,)],

complexes

transition

merization

large out-of-plane for example

7 is found

complexes

5

to 4,

geometries,

number

EJ units betwccn

Bis(cyclopentadieny1)

although

ligands

zirconium.

from

compared

reflecting

{ [Zr(OEP)11(/1-OH)3}

with coordination

&cetate

In addition.

different number

ranging

complexes, metal,

groups

Coordination for example

types are found

bisporphyrin

for

and sixth donor

complex,

numbers

porphyrin

for the central

preferences

of the fifth

Coordination

metal

for the later metals.

observed

Finally,

0x0 or -hydroxo

observed.

for the early

to be reported

in the section

complexes

containing

data for all the structurally

on scangroups

3

charac-

II.

Yttrium, and Lutetium

The

first organometallic

particular

significance

scandium

porphyrin

as it represented

complex

the first

IO be prepared

example

was of

of a porphyrin

con-

plex containing a ?r-cyclopentadienyl Ii&and. The first report was the result of’thc reaction of’ Sc(TTP) with LiCp’ , giving a complex for which NMR data alone was collected. but which showed a resonance at -0.42 ppm attributed to the Cp* protons. shifted markedly upfield by the porphyrin ring current.j’ This was confirmed

by the preparation

which

showed

C(W)

distance

toward

the r-bonded is 2.494(4)

and structural

characterization

Cp ring coordinated A, with the scandium

to scandium

of Sc(OEP)(&?p). (Fig. 3).”

The Sc-

atom displaced from the NJ plane along with the Cp‘ and CsHJMe

the Cp ring by 0.80 r\. This complex, were also prepared. is air stable and sublimable and surprisingly inert to hydrolysis.“‘.“3 A further example. the indenyl complex Sc(OEP)(&CuH7)

analogues which

Transition Metal Porphyrin Complexes

FK;. 3. Molccularstructure\ of selected organometallic groups 3.4. and 6 porphyrin complexes: SctOEP)CH(SiMe~)z.” (h) Sc(OEP)(&Cp),” (c) Zr(OEP)Me~.JX (cl) Zr(OEP)(C_CPh)3LI(THF).~’ le) Ti(OEP)(,I~-PhC=CPh).‘” (t’) Mo(TPP)(Ph)CI.‘”

233

(a)

(prepared from Sc(OEP)CI with NaC9H7) contains a tilted, slipped q’-indenyl ring with slightly longer SC-C distances, ranging from 2.504(8)-2.580(8) A, and a similar SC-NJ plane displacement of 0.78 I&~’ The scandium alkyl complexes Sc(OEP)R. prepared from Sc(OEP)CI with MgMel, Mg(CH2CMej)2, or LiCH(SiMe+, are much more air and moisture sensitive than their cyclopentadienyl counterparts. arising perhaps from their electron poor nature, being formally only IO-electron complexes. The molecular structures of Sc(OEP)Me and Sc(OEP)CH(SiMe& (Fig. 3) showed similar SC-C bond lengths (2.246(j) and 2.243(8) A) and SC-NJ out-of-plane distances (0.66 and

234

235

Transition Metal Porphyrin Complexes

0.7 I k).‘j

The alkyl

products gave

could

complexes

form

acetate formed

yttriutn

and lutetimii

with

M(CH(SiMej)z)j

the alkyl

or aryloxide

crystal

structure

;I Lu-C treatment readily

A. The

with

hydrolyzed

product

Y(OEP)(OAr)

“ate”

AIMcj,

reacts

lfjust

of the catnc

free base

porphyrin

displaced

to

from

the NJ

dimeric which

are

Protono-

alkynyl

do not react with

by

complexes

[M(OEP)]z$-OH),.

counterparts

A with

be interconverted

can

and the alkyl

gives

cotnplexes

dished

atom

ditncrs

the CpzMR

product

two

equivalents

this

time

groups

fluxional

on the NMR insert

complcxex.

hydrogen

do react

in the ‘H NMR in Scheme

time when

which

the strong McLi

is observed The

spectrum.“.”

complex g that

bridging

the cot~~pout~tl

shows distinct

tendency

to give

with

Hz to

ih exposed

signals

The chemistry

with

a reduced

yield

in this system by trcattnent

spectrum

the AIMq (but

the Y,Li-bridged Y(OEP)Me

to with

Y(OEP)(/I-Me)LAIMcl.

in the ‘H NMR

indicatin

scale.

of

can be removed

g the Y.Al-bridged molecule,

to give

adduct

an

is used in the reaction,

illustrating

one peak

in this

oxygen

(/I-OMc)2AIMe2

of MeLi

The coordinated

producin

C, only

of MeLi

essentially

is formed,

complexes.

at -60

groups

with

one equivalent

AI-CH;

rized

a highly

as appropriate,

Y(OEP)(/1-Mc)lLi(OEt2).

LiMe.OEtl.

E\en

unlike

from

or M(OEP)OAr.3J

complexes

usin g t-BuC-CH

The alkyl

complex.

are prepared

Cp:MH.”

complex

form

and alkyl

and

bond.”

= Y. Lu: R = 2,6-C~,H~-t-Bu2)

shows

to the bis-/l-hydroxo cotnplexes

Sc(OEP)OAc

M(OEP)CH(SiMej)z

or HOAr,

[ M(OEP)(C=C-/-Bu)]?.

products,

A and the lutetiutn

aryloxide

LiCHSiMc;

yhis of the alkyl the hydride

complexes

(M

but pure

with Sc(OEP)Me

into the SC-C

complexes

or M(OAr)?

of 2.374(g)

by 0.918

and acetone

by insertion

of Lu(OEP)CH(SiMe3)?

distance

plane

CO and isocyanides.

ofC0,

and t-butoxide

respectively,

Organotnetallic

with

Fast reactions

the well-characterized

Sc(OEP)O-t-Bu, HIOEP

react rapidly

not be isolated.

for all t’out

moiety

is highly

not the terminal) to 0,.

for the 0--CH{ of the yttrium

methyl

forming

Y(OEP)

and AI-C’H: complexes

groups is summ:t-

I

C. Titanium Organometallic compound early

titanium

containing

transition

porphyrin

aTi

metals.

porphyrin

low valent

with complexes in the highest groups 3. 4. 5 and lanthanide Zr(IV)

porphyrin

dialkyl

complexes coordinated

organotnetallic

center

around

a single

to an &lkyne porphyrin

class ot

ligand.

species

For the

are unusual.

available oxidation state predominating for the othct porphyrin complexes surveyed here. For example,

cotnplexes

feature

strongly,

but the Ti(lV)

are as yet unknown. The titanium alkyne cotnplexes complement porphyrin alkyne complexes known, Mo(Por)(PhC-CPh).

analogues

the only

other

236

PENELOPE

I

CH,Li

J. BROTHERS

‘\,,

Hz0

t-BuCzCH \

i/i

OEt, I

[Y(OEP)(C=C-t-Bu)],

jL’\

AI;W ,), I H,C

H,C

CH,

CH, ‘Ai

‘AI /\ -

0. A

Ar = 2,6-C,H,-t-64 Por = OEP S(‘III:hll.

I

Reduction of Ti(Por)Clz with excess LiAIHJ in the presence of an alkync produces the series of alkyne complexes Ti(Por)(RC-CR), where Por is OEP 01 TTP, and the alkyne is diphenylacetylene, 2-butyne. 2-pentyne. or Shexync. An alternative synthesis begins with reduced titanium porphyrin complexes. treating Ti(TTP)CI with NaBEt,H and alkync. or Ti(TTP)(THF), with alkyne alone. The complexcs are diamagnetic and the porphyrin ligands retain their four-fold symmetry even at low temperature indicatin g that there is rapid rotation of the coordinated alkyne ligand. The extremely oxophilic titanium center reacts rapidly with 02 to give the titanium 0x0 complex, Ti(Por)=O.“” ‘* A crystal structure of Ti(OEP)(PhC=CPh) (Fig. 3) reveals Ti-C distances averaging 2.017 w (two independent molecules) and displacement of the titanium atom from the NJ plane of 0.54 r\. The C=C distance and C--CCC angle in the alkyne are I .30( I ) and 142.1(h) ‘, respectively. These data, together with IR and 13C NMR results are consistent with the alkyne l&and donating four electrons, as is the case for the alkyne ligand in Mo(TTP)(PhC=CPh), and contrasts with CplTi(CO)(PhC-CPh) for which the 1R-electron rule requires that the alkyne is a two-electron donor.‘” The alkyne ligand is not displaced by CO or ethene but is substituted by \trongera-donor ligands likepyridine and4-p&line. which give the pammagnetic

Transition Metal Porphyrin Complexes

237

complexes r/.tul.s-Ti(TTP)(L),. Diphenylacetylene and terminal alkynes will displace ?-butyne from Ti(TTP)(MeC-CMe), perhaps because the stronger r-acids will bind more readily to the electron rich Ti(I1) center. This method has been used to prepare the phenylacetylene and ethyne complexes Ti(TTP)(PhC=CH) and Ti(TTP)(HC=CH).‘7 The 3-hexyne complex Ti(TTP)(EtC=CEt) in C(,Db with excess THF exists in equilibrium with Ti(TTP)(THF)z (K,,, = 3.8) but is quantitatively converted to the bis(isocyanide) complex with two equivalents of CN-f-Bu. These observations have allowed the relative preference for binding of a neutral ligand to the Ti(TTP) moiety to be established as follows: pyridine - picolinc > CNR > PhC=CPh > EtC-CEt > THF? Ti(Por)(RC=CR) acts as a source of the Ti(Por) fragment in atom transfer rcactions, accepting a chalcogenide atom from E=PPhj (E = S, Se) to give Ti(Por)=E, and reacting with elemental sulfur or selenium to give Ti(Por)( )12-E?), which in turn react with Ti(Por)(RC-CR) to give two equivalents ofTi(Por)=E. Ti(Por)(Ty2-02) behaves similarly, and the 0x0 complex Ti(Por)=O forms the new. paramagnetic /L0x0 binuclear species [Ti(Por)]2(p-0) upon reaction with Ti(Por)(RC=CR).37.3”.“’ Iminc andorganic azide reagents transfer an imido fragment toTi(TTP)(EtC=CEt), giving Ti(TTP)=NPh or Ti(TTP)=NSiMei from PhN=NPh or N+SiMe+ respectively.“,” Diazoalkanes act as carbene sources with group 8 metal porphyrins. giving M(Por)=CRz (M = Fe, Ru, OS). an interesting contrast with the reaction of Ti(TTP)(PhC-CPh) with N?CAr-, which gives not the carbene but rather the hydraLid complex (Ti(TTP)=N-N=CArl (Ar = 4-Cc,HAMe), reflecting perhaps the preference of an early transition metal for the harder nitrogen donor atom.” The Ti(Por) fragment is formally acting as a reductant in the atom transfer reactions. and this can occur in a one-electron or two-electron sense. The former is illustrated by the reductive dechlorination of vicinal dihalo-substituted organic substrates, in which Ti(TTP)(EtC=CEt) reacts with I .2-dichloroethane. I ,2-dichlorocyclohexane, or I .2-dichloroethene to give cthene, cyclohexene, 01 othync. respectively, together with Ti(TTP)CI as the inorganic product. Twoelectron reductions occur in the reactions of Ti(TTP)(EtC=CEt) with epoxidcs or alkyl- or arylsult’oxides (RS(O)R), producing Ti(TTP)=O and alkenes or UIItides (RSR), respectively.“3 The reactions of the titanium alkyne complexes arc summarized in Scheme 2.

D. Zirconium

and Hafnium

The first organometallic zirconium complexes to be prepared all contained Zr( IV) and were reported almost contemporaneously.J’-‘6 The reaction ofZr(TPP)(OAc)? with RLi or RMgBr produced the dialkyl complexes Zr(TPP)Rz (R = Me, Et, n-Bu or Ph). characterized by spectroscopy.“.J7 The development of the chlorozirconium complexes opened up the chemistry further, with

238

PENELOPE

J. BROTHERS

Zr(TPP)CI?(THF) and Zr(OEP)CI, (prepared from Li?(OEP)(THF), with ZrCIJL1 where L = THF or tetrahydrothiophene) reacting with Li(p-C6HJ-t-Bu) to give Zr(OEP)(/,-C~,H~-r-Bu)~. and with LiR or MgR2 to give the dialkyl complexes Zr(Por)Mcl (Por = OEP. TPP). Zr(OEP)Etz and Zr(OEP)(CH$iMe3)2.‘5.1”.1X Hf(TPP)Mq was prepared similarly from Hr(TPP)CI? with McLi.‘“.“’ All ol‘ the complexes were assigned cis geometry on the basis of the lack 01‘symmetry in the plane containing the porphyrin as evidenced by the diastereotopic CH, protons observed for the OEP ethyl groups. This was confirmed by X-ray crystal structures for Zr(OEP)Me2. CHzCll (Fig. 3) and Zr(OEP)(CH2SiMe3)l which showed Zr-C(av) bond lengths of2.343(4) and 1.2X7(4) A. Zr--NJ plane displacements ot 0.89 and 0.93 r\, and C-Zr-C angles of X2.7( I ) and 78.1 I ( 12) . rcspcctivcly.‘6.‘x Zirconium(IV) ~-complexes containing the IIX-cyclooctatetraenyl (COT) ot qi-dicarbolide anions. Zr(OEP)(q”-COT) or %r(OEP)(& I .2-C2BoH, I ), were prepared from Zr(OEP)C12 with the salts K$YOT or Na$21BoHI ,. rcspectivcly. An X-ray crystal structure of the dicarbolidc complex shows the I/-coordination through the planar C:Bq face (Zr-C(av) 2.57 A. %r-B(av) 1.50 k, Zr--NJ plane 0.904 A) and can be considered an analogue ofthe scandium Cp complex Sc(OEP)(,]5- Cp),lS.Jh.JX.S I The tendency to form “ate” complexes observed for yttrium is also seen in the preparation of a novel zirconium alkynyl complex. Reaction of Zr(Por)Cl2 (Por = OEP or TPP) with either two or three equivalents of LiC=CR (R = Ph ot SiMel) gives the trisalkynyl cotnplexesZr(Por)(C=CR)~Li(THF). An X-ray crystal structure ofZr(OEP)(C-CPh)3Li(THF) shows that all three alkynyl ligands arc on

239

Transition Metal Porphyrin Complexes the same face of the molecule. carbon

atoms,

axis (Fig.

and the THF

3). The average

a and the Zi--N4

plane

sensitive

water,

in solution dine.

and C=C

(/l-OH)i}-

solvents,

Zr(OEP)Mez

Zr(OEP)(OAc)2.

with CO,,

to generate

complexes produces

M(OEP)(CH$iMeT)2 the cationic

solvents (M

using

= Zr, Hf),

Zr(OEP)Et,

complexes

with

by reaction

slowly

ofthe

01

{ [Zr(Por)]l

to give the alkoxide

the ammonium

Zr and Hf complexes

pyri-

are the oxo-

of the dialkyl

Protonolysis

is so

like THE

can also be produced

complex

sensitive

are more stable

of- hydrolysis

Reaction

and ethene.‘x

.Zr

I .2 I8( 12)

are extremely

The complexes

reacts with acetone

The diethyl ethane

light.

which

Zr(OEP)Mez

plex Zr(OEP)(OCMe3)2. solution

bonds

(k~-0)(j~-OH)z

or IZr(Por)]2(E1-OH)J.15.~7.1X.5”

acid produces

the Li.

10) and

Zr(OEP)Q-&HA-t-Bu):

The products

[M(Por)],

the six alkynyl

I .00X A.”

as coordinating

decomposition.

complexes

are 2.323

complex

room

with

to the Li along

distances and Hf-C

normal

in non-coordinating

hydroxo-bridged

Zr-C

and the aryl

even tolerate

interacting

is very large.

containing

or ether promote

acetic

Zr-C

and light,

it cannot

the Li atom

in turn coordinated

displacement

All of the complexes to oxygen,

with

oxygen

ol

com-

decomposes

in

OEP (but not the TPP) salt

[HNMezPh][BPh4]

[ M(OEP)(CH$iMei)l~t

as the BPh4

salts.” The HCI

trisalkynyl

in THF

product

complexes

to produce

CH,=C(Ph)C-CPh

alkyne

HGCR

reaction

silylmcthyl

ethene.

but does

react

of ethane.

and %r(OEP)Et, direct

could xnd

isopropyl

zirconium has been second,

when

by NMR

evidence

zirconium

occurred

complex

degrades

to produce

as the Zr(II1)

complex

ofZr(IV)

to Zr(II1)

of’ the reaction, hydride

for propene,

with

In the absence a green paramagnetic

with the

by H? was unprecedented.

but

complexes

only

n-propyl

of the alkene, the compound which

Zr(OEP)CH$iMe3.”

First, there are very few alkylzirconium(II1)

reduction

directly

and catalyzes

Zr(OEP)(Et)(CH$iMe?)

the course

formed.‘”

HCl.5’

is added,

during

products

added

the coupling

not react

for intermediate

reactivity

organic

has also been observed

does

complexes

Similar

anhydrous of’an

that

with

hydrogen

zirconium

identified

for two reasons.

This kind ofreactivity

of the ethyl

was observed

spectroscopic

be obtained. no

Formation

indicating

Li[CplZr(C=CPh)3]

cthene

with coupled

In the presence

observed.

Zr(OEP)(CH2SiMe3)2

with

react

and the C-C

Zr(OEP)Cl2.

was

complex

complex

HC=CPh

with

to be intramolecular. zirconocene

The

production

along

cross-coupling

no

is likely

for the related

no

Zr(OEP)(C=CPh)3Li(THF)

quantitatively

This complexes

is unusual known,

The compo~~ncl

and can

be prepared directly from treatment of Zr(OEP)(CH$iMe;), with H2 in toluene, and was shown by X-ray crystallography to contain five-coordinate zirconium with a Zr-C

bond length

of 2.2 I6( 8) A and the Zr atom displaced

from

the NJ plane by

0.63 A. Decrease of both these distances relative to the six-coordinate consistent with relief of steric strain. To describe Zr(OEP)CHzSiMe3 cotnplex IJV-visible

is an oversimplification spectra,

together

of its electronic with small changes

structure. in the N-C

precursor

is

as ;I Zr(I11) ‘H NMR. EPR. and

and C-C

bond lengths

240

PENELOPE J. BROTHERS

in the porphyrin core, provide evidence that there is spin density associated with both the Zr atom and the meso carbon atoms of the porphyrins. This indicated that the complex may have some porphyrin radical anion character and that its electronic structure can be described by two resonance forms, Zr”‘(OEP)CH$jiMq and Zr’v(OEPY)CH$iMc3.5’ Two more very important low valent organoLirconium complexes have been reported recently. Reaction of the trisalkynyl complex Zr(TPP)(C=CPh)3Li(THF) with Cp2Ti(Me$iC=CSiMe3) produced, along with other products, the paramagnetic cyclopentadienyl zirconium complex Zr(TPP)(r$Cp). This can also be directly prepared from Zr(TPP)C12 with TlCp using Na/Hg amalgam as the rcductant. A crystal structure of Zr(TPP)(&Cp) shows the Zr-C(a) bond length to be 2.49(2) A. and the Zr-NJ plane distance to be 0.773(S) r\. The EPR and UV-visible spectra of this compound are very similar to those reported for Zr(OEP)CHzSiMe3. suggesting that this compound too might have Zr( Ill) and Zr( IV) porphyrin radical anion character.” The only zirconium(ll) compound to be reported is analogous to the titanium porphyrin alkyne complexes, and was prepared from Zr(OEP)CI, with diphcnyIacetylene and magnesium metal as the rcductant. The diamagnetic product. Zr(OEP)(PhC=CPh), like the titanium complex, contains a formally four-electron donor alkyne Ii&and. The Zr-C bond length and Zr-Nd plane distances. 2.160(4) and 0.90 A. respectively, are larger than those in the titanium analogue as would be expected for the larger zirconium atom. The C=C distance of I .333(X) A is very similar. but the Ph-C=C angle of 133.4(j) A indicates that the alkyne ligand in the zirconium complex is slightly more bent than in the titanium complex.‘” Zirconium porphyrin dicarboxylates have been shown to catalyze the stereo- and regioselective ethylalumination of’alkynes. Although little is known about likely reaction intermediates, NMR evidence for ethyl7irconium complexes was observed (or the products of the reaction of Zr(TPP)(O$?r-Bu)? with AlEt?. attributed to Zr(TPP)(O?C-t-Bu)Et and [Zr(TPP)(II-02C-t-BLi)(,~-Et)]AlMel.’”

Ill THE MIDDLE TRANSITION

ELEMENTS

(GROUPS

$6,

AND 7)

A. Overview The last decade has seen the development of a rich and varied chemistry for organometallic porphyrin complexes of the early transition metals (groups 3 and 4). However, there have been many fewer developments in the organometallic chemistry of the middle transition elements. Despite the paucity of its organometallic porphyrin compounds, molybdenum has played a very important role in

Transition Metal Porphyrin Complexes

241

organometallic porphyrin chemistry. The diphenylacetylene complex Mo(TPP)(,12-PhC=CPh), first reported in I98 I, was the first example of a porphyrin II’alkyne complex, and this class is still limited to a handful of compounds containing molybdenum, tungsten, titanium, or zirconium. At the time this area was last reviewed the molybdenum complex was also the only example of an organometallic porphyrin complex from groups 5. 6, or 7.“.7.x Since then, only a small number of new organometallic porphyrin complexes from these groups have been reported. These include tantalum(V) conplexes, which are most closely related to the high valent zirconium and hafnium complex, a tungsten diphenylacetylene complex. three examples of chromium(II1) a-aryl or a-alkyl complexes, a molybdenum(lV) phenyl complex, and a molybdcnum dichlorocarbene complex. The molybdenum and tungsten alkyne complexes are closely related to the titanium and zirconium examples, all with the formula M(Por)( II’-PhC=CPh). and all formally in the +2 oxidation state. The chromium and molybdenum a-bonded complexes and the manganese carbene have more parallels to the later transition metal complexes containing these Ii&and types. Organometallic porphyrin complexes containing vanadium, niobium, technetium, or rhenium are as yet unknown. X-ray data for the two structurally characterized molybdenum complexes are included in Table II along with the early transition metal complexes. B. Tantalum

Tantalum porphyrins are rare and there has been only one report oftheir organometallic derivatives.57 Treatment of Liz (OEP)(THF)J with TaMeiCY? in C’H,CI, at room temperature gave a good yield of Ta(OEP)Me3. The series of ‘H NMR chenical shifts for the methyl groups in Sc(OEP)Me, Zr(OEP)Me?, and Ta(OEP)MeA (-4.0. 4.5, and -6.0 ppm) illustrates nicely the decreasing effect of the ring current as the ligands move farther away from the center of the porphyrin. Although the compound was not characterized structurally, the lack of mirror symmetry in the porphyrin plane (as evidenced by NMR) indicates that, like the zirconium complexes, the methyl groups are likely to lie on one face of the compound. Ta(OEP)Me3 reacts only slowly with water to form the tris-/l-oxo complex [Ta(oEP)]z(k~-O)j, in contrast to the extremely water-sensitive zirconium alkyl complexes. Unlike the scandium and zirconium complexes. the tantalum complex does not insert CO? or acetone into the Ta-Me bond. However, the compound is moderately light sensitive. A more reactive cationic dimethyl tantalum derivative is produced from Ta(OEP)Mej using one equivalent of the weak acid IHNMe2Ph][BPh,]. ITa(OEP)Me2]+ reacts cleanly with CO to produce acationic enediolate compound, containing the MeC(O-)=C(O-)Me ligand which results from both insertion and

242

PENELOPE J. BROTHERS Li,(OEP)(THF), TaMe& I

IMe ia’

coupling reactions. in a process well known in cyclopentadienyl Tirconocene and tantalocene systems. Treatment of [Ta(OEP)Me21’ with t-butanol gives [Ta(OEP)Me(O-/-Bu)] ’. which then reacts withC0 to form [Ta(OEP)(q’-C(O)Mc) (O-t-BLI)~+. The enediolate and &cyI products are proposed on the basis oi‘theil NMR spectra. as neither could be isolated in ;I pure form.57 Reactions of’tantalum porphyrins are shown in Scheme 3. C. Chromium,

Molybdenum,

and Tungsten

The reaction ofCr(TTP)CI with PhLi, MgBr(p-t-BuCc,HJ), or MgCl(CH1SiMc3) produced Cr(TTP)Ph, Cr(TTP)(/>-r-BuCc,H4) or Cr(TTP)(CH1SiMe3), respectively.“x The Cr(lII)complcxes arc paramagnetic with S = 3/2, and the broadened NMR spectra show temperature dependent shifis which follow Curie behavior. Unlike the earlier transition metals, the compounds can be purified by chromatography on a short plug of alumina. The complexes are moderately air stable in the solid state but very air sensitive in solution. For example. Cr(TTP)Ph reacted with 02 in dry CDCli in the dark to give PhD together with the diamagnetic 0x0 complex Cr(TTP)=O. A radical mechanism involving Cr-C bond homolysis was proposed for this reaction. The aryl complexes react with acetic acid, HgC12. or I2 to give Cr(TTP)X (X = 02CCH3, Cl or I)? A single example of a o-alkyl molybdenum complex was serendipitously prepared from a solution ofthe very light-sensitive dicarbonyl complex Mo(TPP)(CO)I.

Transition Metal Porphyrin Complexes

243

During the course of an attempted recrystallization of this complex From benzene containing chlorinated impurities the solution was exposed to light. The crystalline compound that formed from this solution was identified by X-ray crystallography as Mo(TPP)(Ph)CI (Fig. 3). The complex contains trr~~s phenyl and:hloro ligands. and the MO-C and Mo-NJ plane distances are 2.24 I ( I ) and 0. I25 A, respectively. A systematic synthesis of the complex could not subsequently be developed and consequently other spectroscopic and magnetic data were not collected.‘” The diamagnetic Mo(Il) diphenylacetylene complex Mo(TPP)(II’-PhCsCPh) was prepared by reduction of Mo(TPP)Cl? by LiAlHl in toluene in the presence of excess diphenylacetylene.“” The OEP and TTP analogues containing both molybdenum and. more recently, tungsten, have been prepared similarly.“‘.“’ The short Mo-C and long C=C distances in Mo(TPP)(Tj’-PhC-CPh) were consistent with the alkyne ligand acting as a four-electron donor. This has been supported by a theoretical study. and contrasts with non-porphyrin complexes such as CpzMo(HC=CH) which are constrained by the l&electron rule to contain a two-electron donor alkyne l&and.“” The tungsten porphyrin complexes W(Por)( ,$PhC=CPh) are also expected to contain four-electron donor alkyne ligands. 67 The molybdenum and tunsten diphenylacetylene compounds have been chemically useful primarily as precursors to the quadruple metal-metal bonded dimers [ M(Por)]?, formed by solid-state vacuum pyrolysis reactions.“‘.“’ However. Mo(TTP)(g’-PhC=CPh) is also a useful substrate in atom-transfer reactions. reacting with Sg or Cp-TiSS to form Mo(TTP)=S. The reaction can be reversed by treatment of Mo(TTP)=S with PPhj (which remo\‘es sulfur as Ph;P=S) and PhC-CPh. The order of preference for ligand binding to molybdenum(l1) has been established to be PPh3 < PhC=CPh < 4-picoline.“’

D. Manganese Manganese porphyrin complexes have been widely used as catalysts for oxidation reactions, and the atom transfer properties of the high valent 0x0, nitrido, and imido species have received a lot of attention. However, organometallic manganese porphyrin complexes are limited to one example, a dichlorocarbene complex prepared by the same method as that used for the iron porphyrin dichlorocarbene first reported by Mansuy in 1978. Mn(TPP)CI was treated with CC13 in CH$& under a nitrogen atmosphere. using either iron powder or NaBHa as a reductant. The carbene carbon atom in the resulting complex, Mn(TPP)(=CCl& was observed at 264 ppm by’? NMR spectroscopy. Broad signals were observed for the porphyrin ring in the ‘H NMR spectrum, and this was attributed to the presence of low spin Mn(II). When only one equivalent of a reductant was used in the preparation. a compound assigned as Mn(TPP)CClj was observed by NMR.“”

244

PENELOPE J. BROTHERS

IV IRON A. Overview Iron

porphyrins

alloporphyrin

continue

to be the most

intensely

scrutinized

group

of met-

complexes,

a fact which is no surprise given the importance ot iron porphyrins in electron transfer systems. as oxygen carriers and as biological oxidation catalysts. Interest in organometallic iron porphyrins was sparked

by the observation

that iron o-bonded

complexes.

are formed

Reversible

migration

the deactivation

during

alkyl

cytochrome

of a o-bonded

ofcytochrome

or aryl complexes. PJTo metabolism to ;I pyrrole

l&and

and iron carbene

of certain

nitrogen

substrates.

also features

P450, and has led to close scrutiny

ofthe

in

migration

process.” The synthesis. period

from

in some detail Although

here, this review

will focus

a-bonded

the two classical o-bonded

and electrochemistry

spectroscopy.

1986 to 1988.‘.7.8

will be given Iron(llI)

reactivity,

was described

iron porphyrins

complexes

methods

porphyrins.

a brief

also widely

The reaction

of Fe(Por)X generated

organohalides.

RX gives Fe(Por)R

(R = alkyl.

by iron(I1)

Complcxcs

with

paramagnetic

porphyrins the formula

iron alkyl

spin state of the iron the propertics

atom

I/?

in the ‘1’ Fe(lIl)

alkyl

complexes.

are observed.

Low

ture or solvent.

or aryl

Where

ligand

of alkyl

a relatively small class 01 at the iron center. The

complexes

Fe(Por)R

R and the porphyrin.

is affected

In general.

high

spin

S=

S/2

as a function

can occur

of EPR data for o-bonded

organoiron

by

Fe(Por)R

and Por = OEP or TPP are low

spin conversion

tables

etc.). Capture

] with

IS electrons

R = C(,Fs or C(,F,H,

spin/high

Useful

ligand

RLi.

[Fe(Por)

of synthesis.

constitute

containing

by

and Rh(lll)

with RMgBror

porphyrins.

aryl. vinyl,

method

Fe(Por)R

complexes

of both the axial

R is :I simple

where s =

is a further

can be prepared

of Co(III)

(X = halide) Fe(I)

in the

chemistry

developments.

used for the synthesis

of electrochemically

published

of the early

alkyl or aryl ligands

or the reaction radicals

synopsis

on more recent

containing

of organometallic

in the three reviews

spin,

complcxcs of temperaporphyrins

are given in two of the reviews. ‘.’ NMR spectroscopy has also been used as a probe, with chemical shift differences useful for assigning both the spin state and the location

of spin density.

have been collected

Miissbauer

and compared

data for a-bonded

to non-porphyrin

organoiron

iron complexes.’

spin or,ganoiron(llI) complexes are generally very chemically and thermally sensitive, and susceptible to facile Fe-C bond One-electron oxidation of the Fe(III) obscrvablc Fe(IV) complex, [Fe(Por)R]+. to a pyrrole

nitrogen,

essentially

porphyrins The

low-

reactive. being homolysis.

light

complexes Fe(Por)R can either give an or can induce migration of the R group

an intramolecular

reductive

elimination

process.

Transition Metal Porphyrin Complexes

245

giving the Fe(II) species [Fe(Por-N-R)]+. The migration is reversible, and oneelectron reduction of [Fe(Por-N-R)]’ initiates the reverse reaction to re-form Fe(Por)R. Whether oxidatively induced migration or reversible oxidation occurs depends on a range of factors, including the nature of the R group. Migration was observed for phenyl and tolyl groups, but not for fluorophenyl (CbFs or C~,FIH) or methyl groups. The reasons for the different behavior were not well understood when this area was last reviewed.x For example, it was not believed to be a simple spin state phenomenon. since phenyl- and methyl-iron porphyrin complexes are both low spin, yet phenyl migration occurred whereas methyl migration was not observed. Metal-to-pyrrole nitrogen migration is also induced by one-electron oxidation oforganocobalt porphyrins, although a significant difference is that whereas the initial one-electron oxidation in Fe(Por)R occurs at iron, in Co(Por)R it occurs at the porphyrin ligand. The electrochemistry of a-bonded organoiron porphyrin complexes and also of iron N-alkyl- or N-aryl-porphyrin complexes has been examined in some detail, and early work has been discussed in the rcviews.7.x More recent investigations into oxidatively induced Fe-to-N migration have served to clarify the situation and will be discussed below. The dichlorocarbene complex. Fe(TPP)=CCII, was doubly significant as it was both the first fully characterized transition metal dihalocarbene complex and the first metalloporphyrin carbene complex to be reported.“” It was prepared from Fe(TPP) with CCll using an excess of iron powder.” a method which has been used to synthesize a range of halocarbene complexes, Fe(Por)=CXY, by the reaction 01 Fe(TPP) with CXiY as the carbene source and iron powder or sodium dithionitc as the reductant (X = halide, Y = halide or CN. C02Et. CFj). These carhene conplcxcs containing electroil-withdrawing ligands arc susceptible to nucleophilic attack. and the carbene ligand is transformed to a CO or CNR (isocyanide) ligand on reaction with water or an amine. respectively. Where Y = SR or SeR, reaction ofthe carbcnc with Lewis acids leads to thio- or selcnocarbonyl complexes, Fe(Por)(CS) or Fe(Por)(CSe). When CIJ was used as the carbene source the product was the El-carbido complex (TPP)Fe=C=Fe(TPP). and similarly CI$ZCH(~-C(,HJCI)~ (the insecticide DDT) gave the vinylidene complex Fe(TPP)=C=C(/,-C$,HJCI)~. One-electron oxidation of the vinylidene complex transforms it from an Fe=C axially symmetric Fe(U) carbene to an Fe(II1) complex where the vinylidenc carbon bridges between iron and a pyrrole nitrogen. Cobalt and nickel porphyrin carbene complexes adopt this latter structure, with the carbene fragment t’ormally inserted into the metal-nitrogen bond. The difference between the two types of metalloporphyrin carbene, and the conversion of one type to the other by oxidation in the case of iron. has been considered in a theoretical study. The comparison is especially interesting for the iron(I1) and cobalt(III) carbene complexes Fe(Por)CRz and [Co(Por)(CRl)]’ which both contain d” metal centers yet adopt different structures.‘.“’

246

PENELOPE

B. Iron fl -Bonded

There

has been

methods

relatively

investigations. from

Some

activity

in the development

porphyrin

complexes

on detailed

new examples

Fe(TPP)CI

by ‘H NMR

which

is EPR active.

with

spectroscopy.

complexes

Fe(II1)

decompose

through

temperature

from

Fe-C

contrast

which

in the latter interact.“8

bond homolysis.

However.

of Fe(TTP)CI

with

are the bridged

alkyl pre-

and charac-

is between

by the classical

5 years.

and electrochemical

in toluene-dx

to preparc

the reaction

synthetic

I .4-Cc,HI)Fe(TPP).

I .4-C(,H,)Fe(TPP),

centers

are difficult

or I .4-Cc,HJLiz

An interesting

and (TPP)Fe(/l-

the two paramagnetic

spectroscopic

or (TPP)Fe(/l-

Li(CH,).+Li

of new

over the last 10-l

that have been reported

(TPP)Fe(CH2)1Fe(TPP)

terized

alkyl

little

organoiron

have concentrated

or aryl complexes. pared

Alkyl and Aryl Complexes

for o-bonded

and most studies

J. BROTHERS

Fe(TPP)ChH5.

is not; presumably

Secondary methods

and tertiary

as they rapidly

they can be prepared RMgBr

at -80

at low

C (R = t-Bu.

I -adamantyl).“” Complexes reported.

with

each

2- methylvinyl. C-n-Pr vinyl

unsaturated

prepared

and alkynyl

low

allyl,

and observed

complexes

quickly

tive to be puritied racteristic

Fe(TPP)CI

2.2.dimethylvinyl,

or LiCsCPh)

decompose

ligands

from

to warm although

The vinyl

or isolated

at 25 C, whereas All

dependence

1

(LiC=

4).7”m7’ The

the ally1 species were

and ally1 complexes

the temperature

(vinyl.

reagent

(Scheme

temperature.

have been

Grignard

or lithium

spectroscopy

to room

1.9

and alkynyl)

the appropriate

or 2-methylallyl)

by NMR

by chromatography.

t not observed

CT-allyl.

with

are stable in solution

if allowed

spin behavior.

(rr-vinyl.

too reacshow

ofthe

chavinyl

Transition Metal Porphyrin Complexes

247

complexes show Curie behavior while that of the ally1 complexes shows non-Curie behavior, possibly linked to a spin state change or thermal population of the high spin state.7” Both cis and fmn.s isomers of the 2-methylvinyl derivatives could be identified by NMR.7’ In toluene or CH$ZI? the alkynyl derivatives are high spin, S = S/2 complexes, but are converted to six-coordinate. low spin (S = I /2) complexes on addition of pyridine or THE” Iron porphyrins containing vinyl ligands have also been prepared by hydrometallation of alkynes with Fe(TPP)CI and NaBH4 in toluene/methanol. Reactions with hex-2-yne and hex-3-yne are shown in Scheme 4, with the former giving two isomers. Insertion of an alkyne into an Fe(II1) hydride intermediate, Fe(TPP)H, formed from Fe(TPP)CI with NaBHd, has been proposed for thcsc reactions.7’ In superficially similar chemistry, Fe(TPP)CI (present in IO mol%) catalyzes the reduction of alkenes and alkynes with 200 mol% NaBHd in anaerobic benzene/ethanol. For example, styrene is reduced to 2,3-diphenylbutane and ethylbenzene. Addition of a radical trap decreases the yield of the coupled product, 23diphenylbutane. Both Fe(lII) and Fe(I1) alkyls. Fc(TPP)CH(Me)Ph and [ Fe(TPP)CH(Me)Ph]-, were proposed as intermediates, but were not observed directly.” Six-coordinate organoiron porphyrin nitrosyl complexes, Fe(Por)(R)(NO). wcrc prepared from Fe(Por)R (Por = OEP or TPP: R = Me, n-Bu, aryl) with NO gas. The NMR chemical shifts were typical of diamagnetic complexes. and the oxidation state of iron was assigned as iron(l The electroreduction of iron porphyrins in the presence of alkyl halides is one method for the preparation of a-alkyl iron porphyrin complexes, and the details 01 these electrochemical processes have received oonsidcrable attention. An electrochemical study using four porphyrins, OEP. TTP and two amide-linked “baskethandle” porphyrins showed that, beginning with Fe(Por). both the singly reduced [ Fe(Por)]- and doubly reduced [ Fe(Por)]’ species are alkylatcd at the iron atom. No porphyrin ring alkylation is observed, even though this is a possibility if the reduced species have some porphyrin radical anion character. At low alkyl halide concentrations. a reduced iron alkyl species, formally containing Fe(I), could be observed as a transient. At higher concentrations, catalytic reduction of the alkyl halide by the [Fe”(Por)R] -/[ Fe’(Por)R]‘- couple occurs. The porphyrins containing the amide-linked chains greatly stabilize the reduced species. 7hThe Liseof cteritally hindered porphyrins or alkyl halides was investigated as a means ofdctermining the stability of the four accessible oxidation states for o-alkyl iron porphyrins, which encompass the neutral Fe(II1) complexes Fe(Por)R. the one-electron oxidized and one- and two-electron reduced species. The doubly-reduced complex IFe(Por)]‘~ acts as an outer-sphere electron transfer agent, thus the electroreduction method allows the synthesis of secondary and tertiary alkyl iron complexes normally inaccessible by other means (Fe(I) + R’~ source or Fe(II1) + R- source).”

248

PENELOPE

J. BROTHERS

The reduction ofn-, SW-, and t-butyl bromide, ofrmns- l,2-dibromocyclohexane and other vicinal dibromides by low oxidation state iron porphyrins has been used as a mechanistic probe for investigating specific details of electron transfer 11,s. &2 mechanisms, redox catalysis 11.~ chemical catalysis and inner sphere 12,soutet sphere electron transfer processes.7x~x0The reaction of’ reduced iron porphyrins with alkyl-containing supporting electrolytes used in electrochemistry has also been observed, in which the electrolyte (tetraalkyl ammonium ions) can act as the source of the R group in electrogencrated Fe(Por)R.X’ ‘H NMR spectroscopy studies of iron(II1) m-alkyl and rr-aryl porphyrins have been very important in elucidating spin states. Alkyl and most aryl complexes with simple porphyrin ligands (OEP, TPP. or TTP) are low spin, S = I /2 species. NMR spectra for the tetraarylporphyrin derivatives show uptield resonances f’oi the porphyrin pyrrole protons (CU. - I8 to -35 ppm). and alternating upfield and downfield hyperfine shifts for the axial alkyl or aryl resonances. For /I-alkyl cornplexes, the cw-protons show dramatic downfield shifts (to ~CI.600 ppm), upfield shifts for the B-protons (-25 to - I60 ppm) and downfield shifts for the y-protons (I2 ppm).X2 The a-protons of alkyliron porphyrins are not usually detected as a result of their large downfield shift and broad resonance. These protons were first detected by deuterium NMR in the dcuterated complexes Fe(TPP)CDj (532 ppm) and Fe(TPP)CD$JD3 (562. - I I7 ppm).” For low spin aryl iron porphyrins at 25 C. the ot-tlzo and/‘clr(r protons are shifted upfield (IU. -80 and -20 ppm) and the ttwto protons downfield ((XI. I3 ppm). The contact shifts for the iron-bonded aryl ligands indicated the presence of’r-spin density on these groups. This is consistent with the electronic structure of low spin iron(IIl), with orbital occupancy (rl,y)‘(d,,,,,)‘(rl,~)“(~~~, )J)() which places the unpaired spin in an orbital ofrr symmetry with respect to the iron-ligand bonding. The five-coordinate a-alkyl and rr-aryl complexes will bind a neutral donor ligand (for example, pyridine or imidazolc) to become six-coordinate. but remain as low spin complexes.XJ The fluorophenyl derivatives Fe(Por)(Cc,F5) and Fe(Por)(ChFJH) show spectral characteristics of’high spin. S = S/2 iron(II1) centers. For example. the porphyrin pyrrole CH protons in high spin Fc(TPP)(ChFj) appear at 66 ppm. compared to ~1. -30 ppm in Fe(TPP)(C6H5).“5 The electronic absorption spectra of the products of one-electron electrochenical reduction of’the iron(II1) phenyl porphyrin complexes have characteristics 01‘ both iron(I1) porphyrin and iron(II1) porphyrin radical anion species, and an clectronit structure involving both resonance forms jFe”(Por)Ph]- and [Fe”‘(Por-)Ph] has been proposed.“” Chemical reduction of Fc(TPP)R to the iron(I1) anion (Fe(TPP)R]-~ (R = Et or t?-Pr) was achieved using Li[BHEt3] or K[BH(i-Bu)j] as the reductant in benzene/THF solution at room temperature in the dark. The resonances of’the rz-propyl group in the ‘H NMR spectrum of [ Fe(TPP)(+Pr)l appear in the upfield positions (-0.5 to -6.0 ppm) expected for a diamagnetic porphyrin complex. This contrasts with the paramagnetic, S = 2 spin state observed

Transition Metal Porphyrin Complexes

249

for other anionic iron porphyrins containing halide or alkoxide axial ligands. The reduced alkyl complexes are reoxidized by 02 to the iron(I11) alkyls.x7 The corresponding diamagnetic phthalocyanine iron alkyl complexes, [Fe(Pc)R]-. were prepared by two-electron reduction of Fe(Pc) by LiAIHl to give [ Fc(Pc)]’ (actually the Fe(I) phthalocyaninc radical anion) followed by reaction with MeI. Et1 or i-PrBr. The methyl compound. [Fe(Pc)CHj]- was characterized by X-ray crystallography.8x Electrochemical and spectroelectrochemical studies on high spin and low spin five-coordinate aryl and perfluoroaryl (Ar,;) iron porphyrins containing a variety of porphyrin ligands demonstrated a direct correlation between the spin state of the iron(II1) center and the stability of the oxidized or reduced species. The high spin complexes are unstable upon undergoing a one-electron reduction, but moderately stable if oxidized by one electron. The low spin aryl complexes can be singly reduced to produce a very stable species. but the singly oxidized species undergo a rapid migration of the aryl group.” These studies have been complcmented by MGssbaucr and magnetic studies. The lluorouryl complexes are pure high spin over a wide temperature range. However. for some of the alkyl and aryl complexes which are low spin at 25 C, some high spin sites are observed by EPR spectroscopy in frozen solution or in the solid state. The amount is dependent on the nature of the axial Ii&and and the porphyrin, and in some cases even on the method of sample preparation.‘” For example, Fc(T/ZFjPP)(CbH5) contains a mixture of high- and low-spin iron(II1). The spin state of five-coordinate, low spin Fe(Por)Ph (OEP or TPP) complexes remains unchanged on coordination of pyridint. However. five-coordinate fluoroaryl complexes Fe(Por)(Arp) (Ar,. = Cc,Fi, C(,FJH) are high spin in non-coordinating solvents. but form six-coordinate low spin complexes in pyridine solution.‘“’ The mechanistic details for the electroreduction of the high spin Ruorophenyl porphyrins has been elucidated. The first reduction of Fe(Por)(Arb) is followed by loss of Ar,:-, which then reacts with trace water to produce ArFH and OH , which in turn displaces ArF from the substrate. This chain reaction continues until all the substrate is consumed and converted to Fc(Por)OH which itself reacts to form the /1-0x0 iron(II1) species. This is a mechanism which is unique to the fluoroaryl o-bonded organoiron porphyrin complexes.“’ Even more control over the spin state has been reported by varying the number and substitution pattern of the Ruorine atoms in fluorophenyl complexes. Phenyl complexes containing no fluorine substituents are low spin, whereas the conpounds containing four (Ar 1,~= 2.3,5,6-ChF4H) or five (Arl,5 = C(,Fs) fluorine substituents are high spin. The crossover point occurs for the trifluorophenyl ligand, where the iron complex containing 3,4,5-ChF3HZ is low spin. whereas its isomer containing 2,4,6-CoF3H? is high spin.” A similar situation is observed for iron complexes of the porphyrin isomers porphycenes, in which the pyrrole rings are linked by alternating two- or zero-carbon bridges (Fig. 2). A series of c-aryl iron

250

PENELOPE J. BROTHERS

porphycene

( EtioPc)

three (Al-f;

= 3.4,S-ChF~H~).

was prepared.

cotnplexes

A detailed

ical sturdy showed spin whereas

that Fc(EtioPc)Ph.

propel-tics

complexes in addition The resulting

been

a highly which

to four phenyl

Fc(EtioPc)At

substituents

and electrochem-

t 2. and Fe(EtioPc)Arp; are low arc high spin. Fe(EtioPc)Art:l was

changes

rich

Fe(OETPP)Ph

is at a very

inducts

ever observed

oxidation

is nietal-centered

low pofential

for an iron(lII)

oxidation.

has spectral

[ Fe(OETPP)Phl+[SbCIc,]

consistent

media at I-OOI~~tcmpcruturc. for Fc(OETPP)Ph.

At longer

the second

scan times

oxidation.

The

first reduction.

it

wave

f’ot

with

Thins

independently

an iron(

Alk@her.

phcnyl

facile

media.

S=

organoiron(IV)

and the second

group

I

porphyrin

three reversible

the first at iron

the Fe-to-N

rendering

and is the tnost

can be prepared

is the first n-bonded

idations

in the porphyrin.

in non-aqueous

which

stable in non-aqueous are observed

distortion

the lirst oxidation

porphyrin

features

positions periphery.

of the mncrocycle.

(0.2X V 1‘s SCE)

and the product.

porphyrin (octaethylte-

of the porphyrin

a saddle shaped effects

OETPP

at the /I- pyrrolic

at the IIICSO positions

the electronic

organoiron

ligand,

than OEP or TPP. For cxamplc.

oxidation by chemical

ti)r m-bonded porphyrin

container eight ethyl groups groups

mot-c electron

observed

substituted

steric congcsGon

dramatically

the ring.

fluorine

EPR. LJV-visible)

and Fe(EtioPc)CI

have

containing

traphenylporphyrin),

center.

(NMR,

crystallographically.4~.‘1~

Unusual

which

none (CnHj), two (Art.? = 3,S-ChFzH3),

( ArFJ = 2.3.5,6-C(,FdH)

spectroscopic

Fe(EtioPc)Art:J

characterized

containing m-four

migration

ox-

two

at

OCC~I-s aftet

as ii)r the OEP and TPP analugues.

is

melal-centered.i’i.sh Corrolcs

are tetrapyrt-ok

/llr.scj-carbon

replaced

A corrole cfl’ective

macrocycle than

hears

a porphyrin

role macrocycle

is easier

octaethyl~orrol~

(OEC)

Fe(OEC)CI hibits

with

bond

;I ?-charge

to oxidize coniplex.

role ligand.“’ using Fe(CI04); and Miissbauer cal formulation strong

Fc(OEC)Ph

to porphyrins two

to reduce

of’ PhMgBr.

The

c m bc oxidized,

the presence

and

states.

from

parmqnetic

is niore The

The

compound center.

containing

clectrochetnicully

cor-

the rcaction

01‘ an Fe(IV)

Fc( IV) compound either

form

one atoms.

than a porphyrin.

was prepared

with

carbon

oxidation

Fe(OEC)Ph.

ol‘an air-s;tablc

hut conktin

u-pyrrolic

in its deprotonatcd

and harder

l’our ecluivalcnts

the first example

similar bc(wecn

at stabiliLin, ~7 high

ligand

an S = I spin state, consistent

reprcscnts

from

macrocycles

by a direct

01 t’xand

a tctrapyr-

or chemically.

to give the cationic complex ~Fc(OEC)Ph]CIO~. EPR, UV-visible. spcckoscopy are all consistent with a11 Fe( IV) corrole cation radfw this cotnplex. [ Fe(OEC)PhI~t has an S = I /Z spin state arising antit’erlomapnetic coupling of ail S = I, cl4 Fe(IV) center with an

S = I /3 corrolc radical cation.“x Both IFe(OEC)Phl been characterized by X-ray crystallography (Table

and [ Fc(OEC)Ph]CI04 III).

The

Fe-N(av),

have Fe--N4

plane and Fe-C distance in the cationic complexes arc‘ all slightly shorier than those in the neutral complex. Both cotnplexcs exist as ~-71 dimers with the WIIC tnean interplanar separations oi 3.51 A.“““’

Transition Metal Porphyrin Complexes

251

Only a handful of a-bonded iron porphyrin complexes have been structurally characterized. listed in Table III, and four of these contain porphycent:. corrolc. or phthalocyanine ligands rather than porphyrins.““-“” Selected data arc given in Table III. and X-ray crystal structures of methyl- and phenyliron porphyrin cotnplcxes are shown in Fig. 4. All of the iron(Il1) porphyrin complexes exhibit

(W

ia)

(e)

FIG. 3. Molecular structures of selected organometallic iron porphyrin complexes: (a) F~(TAP)CHI.““’ (b) Fe(TPP)Ph,“” (c) Fe(TPP)(=C=CArd (Ar =p-Cc,H~CI).“’ (cl) Fe(TPP)=C=Re(CO)JRe(C0)5.“” (e) [Fe(OEP)]+C).“’

--

0

254

PENELOPE J. BROTHERS

Fe-NJ

plant

centers.”

displacements

The Fe-C

of over

bond

lengths

2 A) than that in the iron(l1) I’or the phenyl consistent

The

complex

with

oxidatively

summarized with

to [Fe(Por)Ph]-‘,

of the phenyl

elimination

from

porphyrin dication

from

iron, forming

[Fe(Por-N-Ph)]+ to

extensive

[Fe(Por-N-Ph)]+ dergoes

to regenerate While

migration

migration

is initiated

Both

complexes

the formally (effectively

as an iron This

which

length

m-

reductive

N-phenyl

product,

iron

the iron(lll)

themselves

one-electron

been

reduction

iron(l)

transient

Fc(Por-N-Ph)

oxidative

addition

ofthe

C-N

is

oxidacomplex

effectively

have

is

group

then undergoes

the iron

oxidation

“‘4+106 However

bond

Fe(TAP)Me

of a phenyl

nitrogen.

bond.

Fe(lll)

(less than

by a one-electron

is formulated

and its one-electron are stable

complex

configuration.

a new C-N

spin

which

of m-

bond to iron)

Fe(Por)Ph.

this overall

attention

Fe-to-N

iron to a pyrrolc

investigation.

produces

reverse

in the former.

which

low

are shorter

than 2 A). The shorter

bond

process

with

complexcs

to the methyl

electron

group

[ Fe(Por-N-Ph)J’+.

subject

recent

The

an S = I ~ (t/,,)‘(rl,,)‘(~I~,)’

gration

(greater

reversible

S.x”.“‘3

A. consistent

relative

aryl Fe-C

induced,

in Scheme

tion of Fe(Por)Ph

complex

Fe(TPP)Ph

a stronger

0.15

in the iron(lIl)

process

has focused

has been well on the factors

established

controlling

for quite the migration

some

time.‘.‘.”

process.

The

255

Transition Metal Porphyrin Complexes observation gration

that the low spin alkyl

upon oxidation,

apparently niigrntion

oxidation

that either

(iron-centered

complexes

did undergo

mi-

complexes

the spin state at iron or the site

KS porphyrin

ring-centered)

controlled

the

process.

unusual

feature

of tluoroaryl

that they are low spin which

and aryl iron(III)

the high spin tetra- or pentafluoroaryl

did not, led to speculation

of the initial An

whereas

containing

is normally

when

migration

is still

ofthe

the OETPP

oxidation.

but the phenyl whcrc

the miglation

indicating

that

Ii&and

migration

process.

spin

does migrate

occurs

from

leading

However.

despite

oxidatively

induced

state is not the only

Ihe low

also does not undergo

group

This reaction

XC oxidized.

complexes.

step.(‘” Furthermore.

is

OEP and TPP

migration.

the high spin Art; cotnplexcs

not observed,

containing

Fe(OETPP)At-,..

OEP and TPP complexes

low spin porphyrin

in the Fe(OETPP)Arb

the migration

example

complcxcx,

leads to Fe-to-N

that spin state may govern

the IOL~ spin configuration controlling

oxidation

alkyl or aryl ligands

not observed

to speculation

OETPP

to the corresponding

are high spin. One-electron

complexes

iron

in contrast

spin

phenyliron

migration

upon one-electron

ut’ter ;I second

an intermediate

fucto~

complex

oxidation,

two oxidation

the only

le\,els abo\,e

iron(ll1). A very

detailed

recent

of iron

where

Ar = Ph or 3.4,S-C~,F~H~.

C(,FjH?,

aryl

electrochemical

series

porphyrins

X3.S.h-C~,FJH

Fe-to-N

IOM imd high

complexes.

in both

the absence

observation

for the low

r&s

Ibr the high

five-fluorine

spin

complexes

In other

donor

ability

ligunda.

Slower

n-donation that noithcr

words,

the rate conslant

position

the iron(III)

accelerates

decelerates

Alkyliron ;I period

g the miglation. the rate.o2

porphyrin of sevelal

:dong

with

complexes hours

at room

when

migration.

with

important the fastc‘l rind sloucl

ofthc

four-

correlates

with

electron

is coordinated,

whcrcns

coordination

this study

stable

Lability

the rich thus of a

concluded

of the ;u-yl (or :iIkyl)

the iron

~untl

had not previously

pyridine

but that Ihc donor

are not particularly

The

rates for more

Overall.

the

investiguted

subslilucnts)

for miglation faster

and for both

ligand.

these processes

migration,

temperature

Ar = ‘L-I.6

were

the series.

fluorine

spin stllte nor the field strength

is the key to controllin influences

group,

rates are observed group

where

The slow rate for the migration was the reason

migration

in the sixth

fewer

groups

of the aryl

by the aryl

as the sixth

varied

on ;I

complcxcs

leads to an iron( IV) porphyrin.

of the migration

of pyridine (with

spin complexes.

substituted

been observed.

lignd

kinetics

focused

spin

for all of the aryl groups.

The

:tnd presence

electron

donor

migration

study

the low

spin complcxcs

The first oxidation

was that the rate of migration

rates

comprising

and the high

orCc,F5.“’

rind this undergoes spin

and spectroscopic

Fe(OEP)Ar

group

of the n-aryl

in solution,

and ovel

porphyrin

appears.

256

PENELOPE

J. BROTHERS

presumably as a result of Fe-C bond homolysis. The reaction shown in Eq. (I) using the deuteriun-labeled alkyl iodides demonstrated alkyl group exchange. observed by ‘H NMR to have a hall-lifi: of IO0 min for the solution conditions used. The mechanism proposed involved l-?--C bond homolysis, exchange of ,CHj radicals with CD?CDjI to give CDICDI radicals and CHjl, followed by recombination of CDlCD-, with Fe(TPP).X3 The rate of the homolysis process i\ influenced by the nature ofthe porphyrin rin g. with the half-life for decompo.sition of Fe(Por)CH,CHi varying from 4 days for the clcctron rich TAP to 45 min for Flo-TPP. “I’ Fe(TPP)CH3 + CD2CD31 + Fe(TPP)CD?CD{ + CHJI

(1)

The kinetics of Fe-C bond homolysis were investigated using Ph3SnH as a radical trap, which captures R. released from Fe(Por)R in competition with rccombination. The overall reaction is shown in Eq. (2). The bond dissociation activation enthalpies were measured to be 33 kcal mol- for ChHS, 23 kcal mol -’ for CHJ, I9 kcal mom ’for C?Hs. and I7 kcal mol ’forCHzCMe7, with the Fe-C(aryl) bond stronger than the Fe-C(alkyl) bonds. Assuming diffusion controlled rcconbination. the Fe-C bond dissociation energies are expected to be ca. 2 kcal mol-’ lower than these values. The trend in Fc-C(alkyl) bond dissociation cncrgies can be rationalized on steric grounds. The effect ot‘an added base (pyridine or PEt3) was also investigated. Overall, the Fe-C bonds are IO-1 5 kcal mol ’ weaker than the corresponding organocobalt porphyrin metal-carbon bonds. “” Fe(Por)R + PhGnH ---f Fc(Por) + RH + ASnlPhc,

(2)

Nitric oxide (NO) reacts with organoiron(lI1) porphyrins to form six-coordinate adducts. Fe(Por)(R)(NO).7’ Other small molecules (02. SO?. CO) react by insertion into the Fe-C bond, although the nature of the rcaction and the stability of the products varies greatly with both the molecule itself and the organoiron group. AIkyliron(lI1) porphyrin complexes are air sensitive, and when exposed to oxygen under ambient conditions the products are the very stable iron(II1) /~-0x0 dimers, [ Fe(Por)j?O. A more careful investigation revealed that the reaction of the alkyl complexes with oxygen proceeds via insertion of02 into the Fe-C bond.““’ When a solution of Fe(Por)R (R = Me, Et. i-Pi-) is exposed to 02 at -70 C, the characteristic ‘H NMR spectrum of the low spin iron alkyl complex disappears and is replaced by ;I new. high spin species. The same species can be generated from the reaction of an alkyl hydroperoxide with Fe(Por)OH, and is formulated as

257

Transition Metal Porphyrin Complexes CHMe, & +MexMe OH Me,CHOOH

an iron(IIl) alkylperoxide complex, Fe(Por)OOR. These complexes are very reactive and decompose upon standing or upon warming the solution, giving Fe(Por)OH (and eventually the ~~0x0 complex) together with an aldehyde or ketone as the organic product (shown in Scheme 6 for R = i-Pr).“y.x’.“O.“’ The oxygen insertion reaction proceeds similarly for primary, secondary, and tertiary alkyl groups. showing that it is not retarded by bulk in the axial ligand. However, it is sensitive to bulk in the porphyrin ligand, with the reaction proceeding more rapidly for OEP or TPP than for TMP, the latter requiring warming to -SO C to proceed.“” The products of the reaction of 02 with iron porphyrins are not observed, indicating that the mechanism does not proceed via Fe-C bond homolysis as the initial step. Insertion of 02 into ally1 and vinyl iron porphyrins occurs, and the allylperoxy compound was observed by NMR at low temperature, decomposing to acrolein (O=CH-CH=CH?) and Fe(Por)OH upon warming.‘” The low spin aryliron complexes Fe(Por)Ar behave differently than their alkyl counterparts toward oxygen. In chloroform the products of the reaction of Fe(Por)Ar with 02 are the iron alkyl [Fe(Por)Ar]+ and Fe(Por)CI, while in toluene the aryloxide complexes Fe(Por)OAr are formed with no direct evidence for the formation of arylperoxo intermediates.’ ” The high spin iron(II1) alkynyl complexes which have more ionic character in the Fe-C bond do not react with oxygen. and the order of reactivity of organoiron(lI1) complexes toward Oz is given by Fe(Por)(alkyl) > Fe(Por)(aryI) > Fe(Por)(C=CR).7’ One-electron reduction of the iron(II1) alkyl complexes forms the diamagnetic iron(I1) alkyl anions [Fe(Por)RI-. The iron(I1) anions do not react with oxygen directly. but are first oxidized by 02 to the corresponding alkyIiron(I11) complexes. Fe(Por)R, which then insert 01 as described above.x7 Insertion of SO2 into the Fe-C bond in Fe(Por)CH3 was first reported in 1982, giving the sulfinato complexes Fe(Por)SOlCH3, which are moderately ail-stable but can be further oxidized by O2 to give the sulfonato complexes Fe(Por)S03CH3.“3 Alkyliron(II1) porphyrins insert CO to give the acyl complexes Fe(Por)C(O)R. For example, Fe(TPP)C(O)-n-Bu was formed either by this method or by the reaction of [ Fe(TPP)I- with CIC(O)-n-Bu, and was characterized by an X-ray crystal structure

258

PENELOPE

J. BROTHERS

%7rt:\lt. 7.

determination themselves

( IJ~() = I8 17 cm- r).“‘O.’ ” The low spin iron(Ill) react with oxygen

to give the high spin iron(Il1)

Fe(Por)OC(O)R.

The reaction

with the reaction

ofaryliron

peroxoacyl

intermediate

ofthe

acyl species

than alkyliron species

could

with oxygen

complexes

Fe(TPP)OC(O)-/r-Bu.

was also observed

the Fe-C

bond

in the butyliron

complex

Iron(l1)

alkyl

anions

[Fe(Por)R]

do upon one-electron which

can in turn

competes

with

by formation

iron(Il1)

complexes

tion and the latter

do not insert forming The

Fe-C

bond

acyl complexes two reversible irreversible

CO.

failure

Fe(Por)C(O)R

the former

oxidation

(containing

and Fe(l)

TPP, picket

a Lewis

acid. for example

Mg’+,

dramatically

of the catalyst.

facilitates

C-O

bond

rl-PrOH or 2-pyrrolidone) with turnover numbers

breaking.’

BenLyl

undergoing

into

porphyrin.

process is sta-

decomposiupon

re-

to the

of the iron(llI)

as part of this study,

fence

but

and phenyl

CO was attributed

acyl complexes.

and ahowcd

formally) or ;I basket

and one handle

of CO1 to CO at the Fe(l)/Fe(O) after a few cycles. Addition of

improved

The mechanism

reaction of the reduced iron porphyrin type intermediate [Fe(Por)=C(O -)?I,

porphyrin

[ Fe(Por)(Ph)(CO)]-

to insert

porphyrin) catalyzed the electrochemical reduction wave in DMF, although the catalyst was destroyed CO. and the stability

This

iron

The clcctrochcmistry

was invcstigatcd

ofCO1

Fe(Por)C(O)R.

[Fe(Por)C(O)R]-.

adduct,

of Fc(Por)Ph

(to Fe(II) II5 process.

the insertion

Fe(Por)(CO).

with

in the aryl complexes.

reductions

porphyrins

acyl

complex

foi

carboxylato

do not insert CO directly.

and the resulting

a six-coordinate

iron(lI1)

to give the acyl species

to the iron

of Fe(Por)R.

has more in common

7).’ ”

(R = Me, I-Bu)

to Fe(Por)R

of the carbonyl

to iron(

stronger

Iron

be reduced

homolysis

bilized

duction

oxidation

An

from

(Scheme

will

complexes

with 02. as no evidence

be observed.“”

complex.

acyl products

carboxylato

the rate. the production was proposed

[Fe(Por)]’ with CO, in which the presence

to proceed

of by

to form a curbeneof the Lewis acid

If’ The addition of a Briinsted acid (CF~CHZOH. also results in improved catalyst efficiency and lifetime. up to 350 per hour observed. ’I7

259

Transition Metal Porphyrin Complexes

The reaction complex

ofFe(TPP)CI

Fe(TPP)SiMej,

tains low spin iron(lI1). in the ‘H NMR the P-protons through

spectrum-a

silicon

the iron(I1)

to form

porphyrin

paramagnetic

iron(I1)

to Fe(TPP)SiMeJ

to form

a cotnplex

using

assigned

shift

which

has a hallol‘the

is then further

Fe-Si

reduced

by

[ Fe(TPP)SiMe:j--.

12. Fe(TPP)SiMe{

on the basis

to

spin transfet

cleavage

complex

con.2 ppm

compared

The complex

hotnolytic

silyl

at -I

that unpaired

to carbon.

in solution.

the silyliron

The complex

were observed

indicating

compared

the diamagnetic

can be reoxidized lene oxide

small

of ca. 30 min at 25 C. It undergocx

to fortn

LiSiMej

protons

porphyrin,

less efficient

produced

of other products.

tnethyl

surprisingly

iron(ll1)

is much

at 0 C in HMPA

with a nutnber

and the silyl

in /I-butyl

lii’c in solution bond

with LiSiMei along

reacts

of its NMR

This

with

propy-

spectrum

to be

~e(TI’P)(CH2)iOSiMe~.“~ Facile

thermal

of the relatively alkyl

radicals.

hydride

homolysis

of Fe-C

low

bond

R.. Addition

abstraction

with the resulting

from

Fe(TAP)CI

phyrin.

However,

Fe(TAP)SnBu3, observed

with

complex.

The

same

The

stannyl ;I period

‘H NMR with

evidence

signals

source

of Fe(TAP)R

complex

could

was

of hours

low spin be prepared

not particularly

lo produce

sta-

iron

with the existence

to the (Y- and P-protons

of

lead to

of Fc(TAP)

g a psramagnetic,

complex

was consistent

assigned

arises because

and recombination

generatin

over

por-

of low spin

of the butyl

groups

at 8.86 and 5.25 ppm.’ I”

Carbene

The first

iron porphyrin the following

resulted

the overview velopments

Complexes

carbene,

Subsequent of iron porphyrin

substitucnts

of the iron (hex-2-ync

then.

The

or hex-3-ync)

in this section. ” When

was rcporlcd

in l977j

and

developments through the 1980s carbene complexes. mostly with

on the carbene

porphyrins.5,7.x

in this area since

alkynes

Fe(TPP)(=CClz).

year.’

in a range

electron-withdrawing

earlier

radical.

Bu3Sn.

LiSnBu;.

its structure

internal

radical

alkyls

a steady-state

to solutions

and decomposed

C. Iron Porphyrin

which

in iron porphyrin and produces

Bu;SnH

tin by the alkyl

porphyrin

ble in solution

bonds

strength

of excess

tin-centered

(tributyltin)iron(III) from

Fe-C

There reaction

carbon,

of Fe(TPP)CI

to give o-vinyl

the same reaction

have

been detailed

have been relatively with

complexes

is carried

in

few new deNaBHJ

and

was dcscribcd

out using

the terminal

alkynes hex- I -yne or pent- I -yne in toluene/tnethanol the products were proposed on the basis of NMR spectroscopy and mass spectrotnetry to be the dialkylcarbene complexes,

Fe(TPP)(=C(CHi)R)

(R = /t-Bu

or It-Pr, respectively).

tion of the products as curbene complexes would have had the distinctive chemical shift for the carbene carbon

Chtiractet-iza-

been more in the ‘“C

convincing NMR been

260

PENELOPE J. BROTHERS

reported.

Under

the reaction

different

with

solvent

Fe(TPP)(C(=CHl)-n-Bu) the carbene

in addition

fortnation

mediate

hydride.

reduced

(by

(using

Fe(TPP)H,

of the alkyne

was tested

(by

amounts

of methanol)

of the cT-vinyl

The mechanism into the Fe-H

lo give the cT-vinyl

and protonatcd

hypothesis

smaller atnount

to the carbcne.

was insertion

NaBH4)

(Ey. 3). This

conditions

hex- I -yne gave ;I considerable

complex,

MeOH)

using dcutcration

fat

bond of an inter-

which

to give

complex

proposed

is subsequent11

the carbenc

complex

studies.”

$ not observed or isolated

Dihalocarbene displacement

cotnplexes

Fe(TPP)(=CClz) unusual

/I-carbide

cotnplex

pptn

bond.‘“’

in the ‘“C NMR bond

relatively The

Fe=C

bond

pared

in 1981

from

phthalocyanine

than

crystal

Fe(TPP)

and

CI1 togcthcr

tnacrocycles complexes

have

been

with

complexes

prepared

data are sutnmarized more readily

of porphyrin distances.

shorter

I.67

which

short and

a

k

in the

was first pre-

a reducing

agent.“‘.”

containing

A

porphyrin

and struc(urally in Table

OI-

characterized

III (Fig. 4).““”

The

coordinate

axial donors (THE nitro“3m’ counterparts -. 270ne intcrcsting contains both porphyrin and ph-

and phthalocyanine

but slightly

;I very

complexes)

to that of

gen donors, or fluoride ion) than their porphyrin example, IFe(TPP)(THF)](rr-C)[Fe(Pc)(THF)], thalocyanine ligands, and was prepared from Fe(TPP)(=CClz) The structures

;I

at 2 I I .7

llI).‘~O

[Fe(TPP)](jl-C).

of it-on /1-carbido

also contains

showed

carbyne

l‘ot

to give the

was observed

structure

can bc compared

iron cotnplex

illustrated

which

resonance

comparable

by nuclcophilic

nicely

of‘ [Re(CO)5]

(I .957( 12) A) (Fig. 4. Table

since then. and the structural iron phthalocyanine

carbon

An X-ray

in this complex

of othct- examples

has been

Fe(TPP)=C=Re(CO)dRe(C0)5

spectrum. bond

to new carbenes

This

two equivalents

The carbide

bis(porphyrinato)-/I-carbide number

with

( I .605( 13) A. shorter

long Re=C

precursors

substiruents.‘”

by its reaction

rhenium-rhenium Fe=C

are useful

of the chlorine

with

iron /I-carbide

similar

Fe=C

Fc-N(av)

cyanine rations

complexes. reflecting the stnaller hole between the mean macrocycle planes

distances

[ Fe(Pc)]‘-m .‘?’

complexe\

show

for the phthalo-

size in the tnacrocyclc. are also slightly less

Sepafor the

phthalocyanine cotnplcxes. The family of’ porphyrin and phthalocyanine iron /Lcarbido complexes illustrate the importance of the steric protection afforded by the bulky tnacrocycle as only a small number of other transition metal jr-carhido

261

Transition Metal Porphyrin Complexes

complexes have been reported. A single ruthenium analog [Ru(Pc)(py)]$Z has also been reported. “’ The photochemistry of several of the iron porphyrin halocarbene complexes Fc(TPP)(=CXY) (CXY = Ccl?, CBr,, CCIF, CCI(CN) and the vinylidene conplex Fe(TPP)=C=CAr? (Ar=p-C(,H&I) has been studied in degassed benzene at 20’ C using h > 360 nn~.“X.“” Irradiation of the dihalocarbcnc complexes produced Fe(TPP) and the free carbenes :CX2 which were trapped as the cyclopropane derivatives using a variety ofalkenes. The same product ratios were observed when CHX3 and base was used as the carbene source, indicting that ti-ee carbenes are indeed produced from irradiation of the iron porphyrin carbene complexes. The complcxcs containing CCI(CN) or vinylidenc ligands did not form the free carbene. the latter producing Fe(TPP) and the alkyne. ArC=CAr. The photochemical generation of free carbenes from transition metal carbene complexes had not prcviously been observed. and is believed to result from mixing of the porphyrin ,TT“and Fe-C orbitals. This phenomenon is also responsible for the blue-shifted (hypso) spectrum observed for the iron porphyrin carbene complexes. Similar orbital mixing occurs in iron porphyrin carbonyl complexes, which also undergo photodissociation.“X.“‘l The diamagnetic iron porphyrin vinylidene complex Fe(TPP)=C=CAr?(Ar = /~-C~,HJCI) is produced from Fe(TPP)CI. the insecticide DDT (Cl$CH(pC 0H 1Cl) 3 ) . and iron powder’“” and the structure conlirmed by X-ray crystallography (Fig. 4).“’ Oxidatively induced migration of the vinylidene ligand in this complex to give the iron(lI1) Fe-N-bridged vinylidene complex has been reviewed previously.5.“7 The intermediate spin (S = 3/Z) iron(IIl) Fe-N-bridged compound Fc(TPP)(/I(Fe.N)-C=CAr?)CI and theclosely related high spin (S= 3) iron N-vinylporphyrin complex Fe(TPP-N-CH=CArz)Cl (set Schcmc X) were compared in ‘H NMR spectroscopy and crystallographic studies. ‘~11.131 The

Ar,

Ar 1 , Ar

,Ar

H’ Ar,

,Ar

Ar,

/

s

$ HC Fe*+,

(Ar = p-C,H&l)

%‘Hb.Mt

,AI

8.

dc

262

PENELOPE J. BROTHERS

two complexes exhibit

were

clearly

C, symmetry

data were used to assign bridged

distinct

and differ

cotnpound

the vinylidene

brid~e.‘0’~‘0’~‘70

than in the simple An

no fortnal iron(lII)

itnportant

iron oxo intermediates.

for the preparation

reaction

to model

complex.

exhibited

but which

Br2 led to the tnetallacyclic

oxidatively

induced

Fe-N-bridged

complexes,

In an attempt gen atom

visible prcsencc evidence The produced

carbenc

migralion

iron

atom

with Fe(TpCIPP) formulated

and ‘H NMR produced

spectroscopy

N-alkyl

of Fc(T$3PP)CI iron(III)

with

alkylidene

por-

chemistry.

containing

an oxy-

of the diazokctonc was identified

analysis. N-alkyl

Addition

porphyrin.

carbene

of CFqC02H

data recorded

both

N2CHCH7Ph complex

carby UV-

and Brl oxidation

the diazoalkane

Th e .’ spectroscopic

of the

A low spin. diamagnetic

porphyrin,

Fe.N-bridged

of’this

to tot-m via

porphyrin

complexes the reaction

and elemental

a

data consistent

bond.‘“’

in iron

carbene

using gave

C. Reaction

and osmium

was undercahen.

rhc protonatcd

which

by rearrangement

as Fe(TpCIPP)(=C(CH;)C(O)Ph)

the paramagneGc

{ /l(Fe.N)-CHCH2Ph}Cl.

-30

;t Fc-0

to ruthenium

of sodium dithionitc gave the iron I 14 for Fe-to-N migration processex. reaction

‘H NMR

below

potentially

was tested

Fe(TPP)

followed

of the carbene.

are formally

in Eq. (4), proposed

containing

porphyrin

is oxygen

could

This

and

shown

is shorter

III).

cotnplcxes

with

in

to give high valent

Phl=CRl.

carbencs.

and have also been investigated

to prepare

PhC(O)C(N2)CHl

to this rapidly

ylidcs,

was stable only

to give ;I product

on the b-carbon

bene complex

and metal-oxo

complex

structure

(Table

in

involved

P4SO chemistry

UV-visible

arc LW~‘LII as precursors

Diaaalkanes phyrin

Fe-to-N

carbenc

cotnplcxes

porphyrin

is disrupted

nitrogen

in the bridged

in Eq. (4) in a reaction

which

bonding

to iron porphyrins

iodonium

of’ iron

Fe-N

cytochrome

(Phl=O)

utilizing

shown

complex

with a carbenc with

bond

n-bonded

NMR

spin (S = 32) Fe-N-

to Ihc porphyrin

Since metal-carbcne

be used

diamagnetic

The Fe-C

used

a parallel ylide

The

bond

iodosylbenzene

isolobal,

the iodoniutn

Fe-N

porphyrin

reaction from

the fact that they both

and one electron.‘“‘.“’

state in the intermedia(e

as (rl,!)-(c/,,)‘(d!.,)‘(((,!)‘.

with

despite

by one proton

the,ground

this complex.

atom transfer

by ‘H NMR

only

in the

reactions al -30

C

Fc(T/fIPP)

for this complex

wcrc

similar to those observed for the bridged vinylidene analog. Chemical or elcctrochemical reduction of the bridged complex produced the diamagnetic carbene complex Fe(T/KIPP)(=CHCH2Ph), which in (urn can be chemically or electrochemically CH=CHPh)(CI).

oxidized to the iron N-\inylporphyrin complex These reactions are significant in understanding

Fc(T/ICIPP-Nthe proces\

in

263

Transition Metal Porphyrin Complexes which

N-vinyl-heme

dent oxidative

derivatives

metabolism

as a reactive

bridged

vinylidene

was proposed

reaction

The UV-visible

complex, carbene

and

the cytochrome which

Cyclopropanation ethyldiazoacetate

P4SO depen-

involves

NzCHCH?Ph

between

by workup

with

as the final

product.“”

of alkenes

catalyzed

be discussed

in detail

containnitrogen.

aqueous

HCIOJ

or osmium

to involve

metal-carbene

in the sections

by iron porphyrins.

complex

iron and a pyrrole

by rhodium

is known Using

per hour

were observed

and gave t~ur~r.sand ci.v cyclopropane

A mechanism

involving

posed, although

no direct

of the products

(predominantly

cffccts

of the alkene

phyrin

carbcnes

porphyrin

carbene

trur~s) was explained

substrate in the transition withdrawing bearin g electron

using

intermediates.

can

The reaction

I300 turnovers

products

in the ratio

was pro-

intermediates

for these was observed.

evidence

gave the

porphyrins

as the catalyst,

X.X: I .I”

iron

solution

on those elements. Fe(TPP)

of Fe(OEP)-

to that of the Fe. N

to an iron(II1)

attributed bridged

in the reaction

was similar

porphyrin (N$ZHCOzEt)

also be catalyzed

spectrum

was

fragment

times followed

N.N-ethano-bridged

and will

complex

carbene

N$ZHSiMe3.

ing the CHSiMe3 Longer

during

derivative

metabolite.‘“’

An Fe. N-bridged CIOJ with

are produced

of a sydnone

and the stcrcochemistry

in terms

of stereochemical

state. The Mansuy-type iron porsubstituents were not acti\;c 1’01

cyclopropanation.‘“’ The isocyanide studies

have

the general

ligand.

investigated formula with

and will

However,

spin state and spectroscopic

Processes

The cytochrome site using

not be discussed

ligand.

complexes rather

Several

which

these studies

properties

in detail

have

have mostly than chemical

here. Crystallographic

details

is involved

of unactivated

alkanes

of halogenated intermediate

by Iron Porphyrins

of enzymes

as an electron

and the other

active

Catalyzed

P450 family

NADPH

dehalogenation The

with ucarbene

isocyanide

for two of the complexes.“”

D. Oxidation

ylation

isolobal

porphyrin

1Fe(Por)(CNR),]‘.‘3”‘J”

been concerned

water

is formally

iron(II1)

transformations are given

:CNR,

source.

activates One oxygen

in mono-oxygenation and arenes. compounds

in the oxygen

molecular atom reactions

and alkene transfer

at a heme

including

epoxidation.

is also mediated atom

oxygen

of 02 is reduced The reductive

by cytochrome

chemistry

to

hydroxP450.

is a high

valent

iron 0x0 porphyrin radical mechanism of these processes,

cation species. Studies directed at elucidating the ranging from investigations of the intact enzyme

to model

in the laboratory,

compounds

There are many istry. beginning carbene

moieties.

prepared

now

links between this oxidation chemistry with the formally isolobal relationship Furthermore,

iron porphyrin

carbene

comprise

a body

of work.

and organometallic chenbetween iron 0x0 and iron and alkyl

complexes

may

264

PENELOPE J. BROTHERS

play key roles in the so-called green

pigments

and/or

carbene

gen atom

comprising migration

from

interactions,

oxygen

actions

at all. Much

migration

given

a detailed

P450 chemistry mediated

in this review

is beyond

by high

the scope of this review. porphyrins

iron.

carbenc.

agostic

to iron, or

.substrate

inter-

and Fe-to-N

to cytochrome

P450 chemis-

aspects

of cytochrome

and in fact was the subject

P4SO chemistry

(including.

substrate

bridging

has relevance

are still

bonds,

no direct

alkyl

of the oxy-

substrate

Fe-C

or alkene

of the organometallic

the cytochrome

valent

discussed

with

Fe-to-N

of the transfer

to the organic

of carbene,

discussion

in 1987.” Overall.

thoroughly

to the substrate

P450 in which

through

from covalent

of the alkane

of the discussion

processes

try. However,

details

iron intermediate

for this step range

atom transfer

ofcytochrome

are formed

The intimate

some form of coordination

a direct

review

valent

Proposals

inactivation

porphyrins

processes.

the high

under discussion.

“suicide” N-alkyl

and oxidation

but not limited

of a

chemistry

to. iron)

has been

in the literature.‘“m’5

V RUTHENIUM

AND OSMIUM

A. Overview The

early

period

of ruthenium

nated by the coordination M(Por)(CO)L ment

(where

of reliable

dimers,

lit chemistry

routes

magnetic

with

electrons

and a double

bond

by strong

formed.

state pyrolysis

solutions Ru(TMP)

of the dimers is prevented

as a monomer. giving

important

ligands.

the two

in opening

reduction

of the dimers

bond order of zero, and resulting

the monomeric.

formally

Lerovalent

The dimers with

atoms.”

can

the dimers

by treating

tills the r*

dianions,

unpaired

bonding

Ru(II) porphyrin from dimerizing

in cleavage

are para-

two

This

by which

can be reversed

porphyrin

up the organometal-

consistent metal

so the reaction

of M(Por)(py)z,

The develop-

and osmium(ll)

of these elements.

configuration. between

was domcomplexes.

and M(Por)(py),.

with pyridine. The l4-electron by the bulky porphyrin ligand

“I Four-electron

a net M-M

bond to form

donor

Ii&and)

complexes

a (rr)‘(rr)‘(6)‘(n*)’

be disrupted solid

donor

chemistry

and bis(pyridine)

to the ruthenium(II)

has been enormously

of the porphyrin

porphyrin

of the carbonyl

L is a neutral

synthetic

[M(Por)]z,

and osmium

chemistry

are

benzene complex and exist\

and (T* orbit&.

of the metal-metal [M(Por)]‘p.‘J’.‘3’

Al-

ternatively, the M(II) dimers can be oxidized chemically or electrochemically to give the cationic complexes { [M(Por)]2}+ or { [M(Por)]l}‘+ which have metalFinally. the ruthenium dimcrs react metal bond orders of 2.5 and 3, respectively.“’ with anhydrous HX in CH2C12 to form paramagnetic Ru(lV) halide complexes. Ru(Por)X2

(X = F, Cl, Br).lJ7

The

neutral

and oxidized

dimers.

the monomeric

TransitionMetal Porphyrin Complexes

265

PY PY

HX I

dianions, and the Ru(IV) porphyrin halides have all been significant as precursors to new organometallic complexes. The formation and interconversion of these important precursors is shown for ruthenium in Scheme 9. The first ruthenium porphyrin organometallic complexes were reported in 19X5 an(j ,c)t(~,14x113.135and although these early examples have been reviewed,5.7.X more recent chemistry has helped to tie the whole area together. For this reason, the organometallic chemistry of ruthenium and osmium porphyrins will be discussed here in its entirety. In addition, a wider range of organometallic ligand types is found for ruthenium and osmium porphyrin complexes than for any other group of metalloporphyrin complexes. The bulky ruthenium TMP complex Ru(TMP) is very electron deficient in the absence of any coordinating ligand, and a n-complex with benzene has been proposed. In fact, it readily coordinates dinitrogen, forming the mono- and bis-N, adducts Ru(TMP)(Nz)(THF) and Ru(TMP)(N+. “‘.“’ As a result, the use of the TMP ligand for careful stereochemical control of the chemistry at the metal center. which has been very successful for the isolation of elusive rhodium porphyrin complexes, is less useful for ruthenium (and osmium) because of the requirement to exclude all potential ligands, including even N?. Over the last decade a number of high oxidation state ruthenium porphyrin complexes containing oxo or imido ligands have been reported and have been thoroughly studied for their role in oxidation and atom-transfer chemistry. Although comparisons can be drawn with organometallic species (carbene, imido. and 0x0 ligands are formally isolobal) the chemistry of the oxo and imido complexes is beyond the scope of the review and will not be covered here.

PENELOPE J. BROTHERS

266 B. Ruthenium The

first

zerovalent nium(lV)

ruthenium dianion,

dialkyl

ternatively, duce

and Osmium m -Bonded Alkyl and Aryl Complexes porphyrin

[Ru(Por)]‘complexes

the Ru(lV)

Ru(Por)Mq

alkyls

Ru(Por)Mel

precursors

or Ru(Por)Arl

are shown

an

result.

complex

The reaction

dcnce

(Por =OEP, with

where

MeLi

TTP).“’

or ArLi

X = H. Me,

by both methods,

the

the ruthcAl-

to pro-

OMc.

F OI

and Os(Por)R, representative

and interconversion

ofruthcnium

are shown in Scheme IO. of the dianion with alkyl halides

to produce

a

product is better lormulated as ;I rr-complex 01‘ below in the section on alkenc and alkyne complexes.

reaction

of the dianion

for a metallacyclobuta~le.

but instead

with

I .?-dichloropropanc

free cyclopropane

leads to loss ol‘ one of the axial

ligunds

and

gave no cvi-

was detected

analysis and the porphyrin product was Ru(TTP)(THF)y.“’ Therrnolysis of the Ru(IV) dialkyl or diary1 porphyrins in benzcnc

from

giving

by usin, ~7 I ,2- or I .3-dihalonlkane!,mes did not indeed give this was sucessful, but the of [ Ru(Por)]’ with I .?-dibromoethnne

resulting metallacyclopropanc ethenc. and will be discussed The corresponding

prepared

have been reported.‘J3.‘“‘Some

in Fig. 5, and the preparation

porphyrin alkyl and aryl complexes Attempts to exploit the reaction ci.s-dialkyl

react

be prepared

were

or iodocthane,

or Ru(Por)Et?

Ru(Por)X, (Ar =I>-C,HJX

Cl). “‘~“‘) The osmium analogues where R z Mc, Ph and CH$iMq structures

to be reported

with iodomethane

M(Por)R? formal

reduction

RX

\.I /

RLi

Ph

A

THF R = Me or Ph. unless specified %‘Htklt.

10

by CC

at 100 C of the

Transition Metal Porphyrin Complexes

267

(4

orp~~m~ctdlic Iruthenium d osmium FIG. 5. Molscular structure\ of wleckxl (c) O\(TTP)(CH:SiMc7)~. phyrin complexes: (a) Ru(OEP)Ph”’ (b) IRu(OEP-N-Ph)Ph]+,‘i7 IhX (c) O(TTP)(=SiEt~.THF)rTHF).‘“’ (d) O\(TTP)(=C(/,-ChH,Me)~)(THF).

parI ill

metal center to give the corresponding Ru(III) alkyl or aryl complexes Ru(Por)R (R = Me, Ph).‘J”.‘s’ On closer inspection, the reaction of Ru(OEP)CI? with PhLi actually gave both the Ru(IV) and Ru(III) phenyl products Ru(OEP)Phz and Ru(OEP)Ph in 30 and 50% yield, respectively. The two complexe\ could be separated by chromatography. I52 Is1 The reaction of Ru(OEP)CIz with neopentyl lithium gave only the ruthenium(II1) product, Ru(OEP)CH7CMe3.“’ Reduction of the Ru(Il) dimer [Ru(OEP)jz with two equivalents of potassium naphthalide

268

PENELOPE

J. BROTHERS

gave the Ru(1) anion, [Ru(OEP)] characterized on the basis of it\ reaction with Mel which gave Ru(OEP)Mc. This tncthod was also used to preparc the osmium analogue. OS(OEP)M~.“~ Alternatively, oxidation of the ditner by Ag’ IO form the Ru(III) dimer dication (Ru(OEP)]~” and reaction of’ this with Grignard ot diorganozinc compounds gave Ru(OEP)R (R = Mc. Et. Ph. p-Cc,H4Me).“’ This tnethod walr used to prepare cofacial bisorganomctallic diporphyrins. The cofaciul diporphyrin H4(DPB) contains two oclacthylporphyrin units linked through thcit 117~x0 positions by a biphenylcne group. In Ruz(DPB) the two Ru(I1) centers arc the correct distance apart to form ;t Ru=Ru double bond, which can be oxidiazd to form [Rul(DPB)]” which reacts with Griqnard rcagenta to form M2R1(DPB) where R = Me, />-C’~,HJM~or 3.S-C~,H~(CF3)2:t”’ New complexes can be formed by redox chcmistty. One-electron oxidation (by Ag +) of Ru(OEP)Phz led lo migration 01‘one phenyl group from ruthenium lo a porphyrin nitrogen atotn , giving the Ru(lll) complex [Ru(OEP-N-Ph)Ph]+.‘5’ while one-electron oxidation (by Ag ’) of Ru(OEP)(Me)(THF) gave the Ru(lV) cotnplex [Ru(OEP)(Me)(THF)j ’.I” Ru(TPP)Phl ib air stable in solution in the dark, but in atnbient light slowly reacted with air in toluene 10 give the diamagnetic /L-0x0 Ru(lV) complex [ Ru(TPP)Phl20. This ia the lirst organomctallic example of the well-known family of/l-oxo dinuclcar complexes in which a halide. OH. ot OR ligand takes the place of the phenyl group.i’x Two organometallic complexes formally containin g Ru(ll) have been reported. IRu(OEP)RI-m was t’ormcd either by sodium naphthalide reduction ofRu(OEP)R2 with Iosaol’R (R=Me. Ph)‘i3.‘5J.‘5X ot by one-electron reduction ofRu(OEP)Ph.‘” In a second example, further reaction of Ru(OEP)CH2CMe: with neopcntyl lithium gave the unusual dinuclear cotnplcx [Ru(OEP)CH~CMe;]$/~-Li)2.‘i’ [ Ru(OEP)Ph 1 reacts with Mel to give the unsymmetrical Ru(lV) complex Ru(OEP)(Ph)(Mc).‘55 The paramagnctic diporphyrin complexes M?R$DPB). containing two Ru(ll1) centers, undergo successive reductions to form [ MJR,(DPB)]~ and diamagnclic [ M2Rl(DPB)]’ , containing RLI(III)/R~(~~) and two Ru(ll) ccntcrs . respectively.‘5” One further category of cT-bondcd ruthenium and osmium complexes contains nitrosyl ligands. Reaction ofRu(TTP)(NO)CI with aryl or alkyl Grignard reagents led to Ru(TTP)(NO)Q&HdF) or Ru(TTP)(NO)Me.“” The analogous osmium complexes were prepared beginning from Os(OEP)(NO) which was oxidized by NO+PF(L to the cationic intermediate IOs(OEP)(NO)]’ (not isolated) which was then treated with Grignard reagents to give Os(OEP)(NO)R (R = MC, Et, i-PI-, t-Bu,/K6HaF). The thionitrosyl osmium cotnplex Os(OEP)(NS)Me was prepared from Os(OEP)(NS)CI with MeMgBr.‘” Most of the various complexes reported above have been isolated and charactcriLed by a range of spectroscopic techniquca. although some. like the rcdox products were only observed in solution by [Ru(OEP)R]- and [Ru(OEP)(Me)(THF)]‘.

TransitionMetal Porphyrin Complexes

269

‘H NMR spectroscopy. The complexes which have been structurally characterized are Ru(OEP)Ph, Ru(OEP)CH2CMe3. [Ru(OEP)CHICMe3]2(/1-Li)2, [Ru(OEP-NPh)Ph]BFJ, Os(TTP)(CH$iMe&, Ru(TTP)(NO)(&,H4F). and Os(OEP)(NS)Me, and some structural data for these are give in Table IV. They are a sufficiently diverse set of compounds such that it is difficult to draw direct comparisons between them. However. the Ru(II1) complexes appear to have shorter Ru-C bonds than the Ru(ll) compounds. The OEP-N-phenyl complex [ Ru(OEP-N-Ph)Ph]BFJ cxhibits an agostic Ru. .H interaction (2.52 A) involving the ort/?o-hydrogen of’the OEP N-phenyl group.“‘The complexes containing bulky neopentyl or CHzSiMe3 groups show considerable distortion arising from steric factors, including N-M-C unglcs bent significantly away from the 90 expected in idealized geometry, and angles at the neopentyl CH2 groups much larger than the ,s$ angle of’ I09 .““.“’ [ Ru(OEP)CH$ZMe~]Z(/~-Li)2 is composed of’two Ru(OEP)CH$ZMe3 fragments doubly bridged in ;I faceto-face fashion by two Lif cations. which are each rr-complexed to a portion of’the Ru(OEP) group.‘5’ In Ru(TTP)(NO)(p-Cc,HdF) and Os(OEP)(NS)Me the nitrosyl and thionitrosyl groups are bent.“‘.‘5” The Ru(I1) complexes [Ru(OEP)CH2CMe3]~(~~-Li)2 and [Ru(OEP)R] . and the nitrosyl and thionitrosyl complexes Ru(TTP)(NO)@-C,HAF) and Os(OEP)(NS)Me (whose oxidation states are not trivial to assign) are diamagnetic. 10.15?~155.15x.15’~ The Ru(lV) and Os(IV) porphyrin complexes M(Por)R, are also diamagnetic, in contrast to the dihalide species Ru(Por)X? and the single example of’s mononlkyl or -aryl Ru(IV) complexes. [Ru(OEP)(R)(THF)]+ (R = Ph. Me, observed spectroscopically), which are paramagnetic. 1-13.117.I-Ix.I~f~.l~1.lix A low spin electron configuration (t/,,)‘(d,.,)’ is proposed for the diamagnetic dialkyl or diary1 complexes. In the dihalo species, r-donation from the halide ligands raises the energies of’thc tl,, and d,, orbitals and results in a paramagnetic (tl,,)‘(tl,,)‘(d,,)’ configuration.“’ As expected, the Ru(II1) and Os(III) complexes M(Por)R are low spin, paramagnctic complexes with S = I /2. although they exhibit well-resolved, paramagnctA linear dependence of the chemical shifts on temperature indicates Curie behavior and a single spin state over the range 200~350 K.“’ The N-phenyl Ru(III) complex [Ru(OEP-N-Ph)Ph]+ is also parama~netic.‘“.“J The chemical reactivity of the organoruthenium and -osmium porphyrin complexes varies considerably, with some complexes (M(Por)R?, M(Por)R and Os(OEP)(NO)R) at least moderately air stable, while most are light sensitive and stability is improved by handling them in the dark. Chetnical transformations directly involving the methyl group have been observed for Ru(TTP)(NO)Me, which inserts SO2 to form Ru(TTP)(NO){OS(0)MeJi5” and Ru(OEP)Me which undergoes H, atom abstraction reactions with the radical trap TEMPO in benzene solution to yield Ru(OEP)(CO)(TEMPO). Isotope labeling studies indicate that the cat-bony1 carbon atom is derived from the methyl carbon atom.‘“” Reaction of ically

shifted

'H

NMR

spectra,'.'x.'~'.'~'.'"'

271

Transition Metal Porphyrin Complexes

CWH, QDCH,CH3 ~~

~

+=

&

+ .CH,CH,

’

[e]

+ CH,CH, -

x

+ .cH&Hz

+ CM&H,

&

+

Ru + CH,CH, CH,CH, d

[g]

.

H,C=CH,

P

2

OCH,CH, k CH,CH2.

+ TEMPO “::rri

S(‘HIhll, I I.

the diorganoruthenium complexes Ru(Por)R? with HBr leads to cleavage of the Ru-C bond and formation of Ru(Por)Brl.“’ The five-coordinate Ru(III) complexes Ru(Por)R will coordinate 21 sixth. neutral ligand to form RutPor)(R)L. where L = pyridine, PPh3. etc.” The diethyl ruthenium porphyrin compound Ru(OEP)Et,, upon standing in benzene at room temperature for ;I few hours. converts to ;I I :2 mixture ofthe ethylidene complex Ru(OEP)=CHMe and the Ru(lII) ethyl complex Ru(OEP)Et, Ltlong with ethane and ethene. Kinetic studies using TEMPO as a radical trap are consistent with Ru-C bond homolysis in Ru(OEP)Et? as the first step in the mechanism shown in Scheme I I. The Ru-C bond dissociation energy ( AHt) was determined to be 23.7 31 0.5 kcal mo-‘, which represents the upper limit for the Ru-C bond energy in this complex.‘@ Kinetic studies on the thermal decomposition of Ru(Por)Ph, to Ru(Por)Ph and biphenyl allowed determination of upper limits for the Ru-C hond energies in these complexes to be 3 I .6 * 0.5 kcal mom ’ for the OEP complex and 34.2 f 0.6 kcal mom ’ for the TPP complex. Comparing all these values. the phenyl Ru-C bond is ca. 8 kcal mo-’ stronger than the ethyl Ru-C bond. Lundthe phenyl Ru-C bond is stronger by 2.6 kcal molin the TPP relative to the OEP complex, consistent with a stronger RLI-C bond in the complex containing the less basic porphyrin ligand.‘3X.‘5’ The stronger Ru-aryl bond strength is reflected chemically in the decomposition of Ru(OEP)(Ph)(Me) which slowly forms the five-coordinate phenyl complex Ru(OEP)Ph on standing in the solid 5t’‘tte.‘55 The redox chemistry of the ruthenium aryl and alkyl porphyrin complexes has been very thoroughly investigated. including both electrochemical and chemical

272

PENELOPE J. BROTHERS

oxidation

and

plexes,

reduction.

This

as summarized

redox

processes

themselves.

and [Ru(OEP-N-Ph)Ph] rired

in Scheme

formal

complex

vation

as

level

chemistry

by electrochemistry

of their

‘H NMR

in the scheme).

consistent

Ru(OEP)Ph,

spectra,

results

with

a

oxidants

interest

(X-ray

(The

porphyrin

one-electron

of one phcnyl

radical

structure)

anion.)

arrows

oxidation nitrogen

[ Ru(OEP-N-Ph)Ph]

+$

-e t R +4

d

+

RU

RU &

THF

THF

R

,,’

+e

+e it

\

1

+2 THF

Ph t not observed.

The

by obser-

by heavy

to a pyrrolic

complex

level.

transformations

(shown

group

rc-

oxidation

is the fact that one-electron

crystal

is \umm;lat the same

has been corroborated

or reductants

R Ru eJ R

+5

line.

at the Ru(III)

Ru(lV)

in the scheme

in rapid migration

give the well-charcaterized

so that complexes

formally

comof the

Ru(OEP)Ph,

in THE

and some of the electrochemical

using chemical

Of particular

is arranged

although

of new

understanding

of Ru(OEP)Phz.

on the same horizontal

of most of the species

have been repeated

thorough

elucidated

appear

features

to the syntheses

to a very

also

The redox

[Ru(OEP)Phzl-.

has spectroscopic formulation

’.

but

I 2.‘53.‘5J The scheme

oxidation

duced

has led not only

above,

llfetlme

very

short

of to c

TransitionMetal Porphyrin Complexes

273

(Fig. S).ls7 One-electron reduction ofthis complex results in the reverse migration and reforms Ru(OEP)PhZ. In each case, the initial one-electron oxidized or reduced species has a very short lifetime and is not observed directly. This chemistry contrasts with the one-electron oxidation of Ru(OEP)Ph, which does not result in phenyl migration, and gives the Ru(IV) product [Ru(OEP)Ph]+. Scheme I2 also applies for the redox chemistry of the dimethyl complex Ru(OEP)Me,.‘“’ The only significant difference is that ]Ru(OEP)Me]-. is believed to form by loss of CH? from [Ru(OEP)Me2]-. in contrast IO [Ru(OEP)Ph]- which is produced by loss of Ph- from [Ru(OEP)Phl]‘-. The properties of the highly oxidized and reduced transient species [Ru(OEP)Ar2]’ and [Ru(OEP)Ar2]- , respectively, were investigated by studying the electrochemistry of a series of complexes where Ar = /‘-C(,HJX. and X = H, Me, OMe, Cl or F.“”

C. Complexes

with JI -Bonded Ligands

The Ru(IV) dialkyl complexes Ru(Por)R? (R = Me, Et) were first prepared by the reaction of the dianion Kz[Ru(Por)] with the corresponding alkyl halide in THF.“j When 1,2-dibromoethane was used, the resulting product c;m be formulated either as the Ru(IV) metallacyclopropane. or as the Ru(II) ethene conplex, Ru(Por)(H$=CH2). and indeed the reaction of the dimer [Ru(Por)]? with ethene gas gave the identical product (Scheme 13). Reaction of [Os(TTP)]’ with I .2-dibromoethane gave the osmium analogue, Os(TTP)(H2C=CHI). The ethene protons appear as a singlet at -4.06 ppm in the ‘H NMR spectrum of Ru(TTP)(H$=CH?), an uptield shift of 9 ppm relative to free ethene.‘4’.‘43 The dinitrogen ligands in Ru(TMP)(N?)?can be displaced by alkene or alkync ligands in Cc,Df,.Ethene coordinated to Ru(TMP) has been observed by NMR (6 -3.27 ppm).

CH,,CH,

J

BrCH,CH,Br

274

PENELOPE J. BROTHERS

and a broad (CbHttt).“’

peak

appears

for the alkene

Phenylacetylene

Ru(TMP).

again with clear ‘H NMR

phenyl

groups

-7.40

ppm in Ru(TMP)(PhC-CH).

with

one

solution:

prolons

of cyclohexcnc

and diphenylacetylene

in both complexes.

evidence

formed

for uptield

shiticd

and the alkyne

hydrogen

The alkene

complexes

equivalent of THF observed 1-l: and the isopropanol adduct

in Ru(TMP)-

1: I n-complexes

with

resonances

in PhC-CH

for the

appears

at

can be six-coordinate.

I’m- Ru(TTP)(CH7=CH1)(THF) Ru(TMP)(CH?=CH?)(

in C&,

has also

i-PrOH)

been reported.‘“’ In contrast, bient

light

the reaction

in order

for the CzHz group indicating chiometry, which

rather

integrated

confirmed

by

could be isolated.

[ Rh(OEP)]?

with

than

:spectrum

for I proton a

which

Rh-CH=CH-Rh(OEP).

with

complex

from the ruthenium

peak

coordination

weight with

of the product.

dctcrmination.

bridging

the CH protons

anppm

In addition,

unit. represcnting

at -9.92

product. (TMP)-

of the rhodium

alkenyl

by CO or phosphites

2: I stoi-

The

bis(carbene).

the reaction

the

requires at 10.44

n&c.

to be the bridging

gave

placed

in C&,

shifted

per Ku(TMP)

molecular

was dcduccd

ethyne

ethyne

(6 “C = 264 ppm)

;I r-alkcne

and contrasts

Ru=CH-CH=Ru(TMP),

with

and gave a downfield

in the ‘H NMR

a carbenoid

the CzH2 resonance

of Ru(TMP)(N?)?

to proceed,

pp.

product

can be dis-

Ethyne

(I~). giving

dimct(OEP)-

the free alkyne

and Ru(TMP)L?.‘“’ The details

most

recent

the rcaclion

report

to ;I ruthenium

of n-coordination

of [Ru(OEP)]~

with

Ct,t, in benrene/THF

porphyrin

Il-agtnent

( 100: I ) solution.

The

a new band at 7X0 nm. not observed in the spectrum of either ]Ru(OEP)]z or Ct,t,. and ‘H and “C NMR data also indicated the presence of ;I new complex. This has been l’t~rmulated on the hasi

UV-visible

spectrum

of the spectroscopic

Ruthenium first alkyl routes

of the complex

data as the lullercne

porphyrin

and alkene

either

using

showed

carbene complexes,

the dianion

complex

complexes

Ru(OEP)(t~~-Ch,,).‘t”

were rcportcd

reaction of the ditner [ Ru(Por)], with a diazoalkanc mer route was used to prepare Ru(TTP)=CHSiMei Ru(TTP)=C=C(/K~,H~Cl)~, tively.

and the latter

tnethod

at the same time ax the

and can be prepared by the two complementary with ;I getninal alkyl dihalide or by [Ru(Por)]’ (Scheme I 3).‘J’.‘J” and the vinylidene

using Cl?CHSiMel

and CI~C=C(/~-C~,HJCI),.

for Ru(Por)=CHCO,Et.

using N$ZHCO~EI The use of diazoalkane

diazoacetate) (Por = OEP, TTP. TMP).‘i’.“3.‘“” to form ruthenium porphyrin carbene complexes

has very

recently

The f’orcomplex respcc(ethyreagents

been detnoi-i-

as the complex by this method was

stratcd to bc effective using the carbonyl complex Ru(TPP)(CO)(EtOH) ruthenium precursor, avoiding the laborious conversion of the cw-bonyl to the ruthenium dimer. The preparation of Ru(TPP)(=CRR’) demonstrated using N$HCO:Et, N&(C02Et)2 and N$Z(Me)COIEt.‘“’

Transition Metal Porphyrin Complexes

275

The vinylidene complex Ru(TTP)=C=C(p-C6HIC1)2 has been prepared by an alternative route. using RUDER to insert ruthenium into a free-base porphyrin already containing the vinylidene fragment bridging between two adjacent pyrrole nitrogen atoms. Two further novel compounds which contain a disrupted porphyrin ring are also produced in this reaction. The first compound still essentially contains the vinylidene moiety bridged between two adjacent nitrogen atoms. However, a pyrrole N-C bond of one of the vinylidene-linked pyrrole groups has been ruptured by oxidative addition to ruthenium, forming Ru-N and Ru-C bonds. The ruthenium coordination sphere is completed by the other two pyrrole nitrogens and two CO ligands. The second compound is closely related. but contains a saturated N.N’-CHCHAr? bridging group. The chemistry is reversible, and heating the disrupted ruthenium porphyrin vinylidene complex at I.30 C in chlorobenze repaired the porphyrin and reformed the axially symmetric vinylidene complex Ru(TTP)=C=C(p-ChHJCl),. If15 Neither the reaction of [Ru(Por)]’ with CH$& in THF nor that of [Ru(Por)]l with diazomethane in THF yielded the anticipated methylidene complex Ru(Por)=CH,. Instead, each reaction resulted in equimolar mixtures of the ethylene complex Ru(Por)(CH2=CH2) and the bis(THF) complex Ru(Por)(THF)?. possibly through bimolecular coupling of putative ruthenium methylidene fragments. ‘Q”’ An ethylidene complex, Ru(TTP)=CHMe. can be synthesized from [Ru(TTP)]‘with Cl$ZHMe. or from [Ru(TTP)]? with N$XMe, and observed by ‘H NMR with the distinctive carbenoid proton resonating at 13.03 ppm.“‘l.“’ However. this complex undergoes further reaction in solution. eventually rearranging to form the isomeric ethene complex, Ru(TTP)(CH,=CHz). The ethylidene and ethene complexes are also observed as the decomposition products formed from the diethyl complex Ru(TTP)Etl. As illustrated in Scheme I I these three species are linked by hydrogen abstraction processes initiated by Ru-C bond homolysis in the diethyl complex.‘J5 Osmium porphyrin carbene complexes have been prepared by reaction of [Os(TTP)]l with diazoalkanes, forming Os(TTP)=C(/KI,HJMe)7, Os(TTP)(=CHSiMe3). and Os(TTP)=CHC02Et.‘“” In an important extension of this work, osmium silylene complexes were prepared either from the reaction of [Os(TTP)]? with hexamethylsiiacyclopropane (eliminating MelC=CMe7 and forming Os(TTP)=SiMe?.THF) or, more conveniently, from [Os(TTP)]‘- with C11SiR2. This latter method was effective for R = Me, Et or i-Pr, but not for t-Bu or Ph, and in each case gave the silylene-THF adduct Os(TTP)(=SiRl.THF).‘“’ The porphyrin ligands in the diamagnetic ruthenium and osmium carbene complexes generally exhibit four-fold symmetry by NMR, indicating that the barrier to rotation about the M=C bond is low. The carbenoid protons appear shifted downfield in the ‘H NMR spectra, for example appearing for Ru(TTP)=CHCO?Et and Ru(TTP)=CHSiMei at 13.43 and 19.44 ppm, respectively, and for the osmium Downtield shifts for analogues at 21.60 and 28.95 ppm. respectively. IJ2”J.i’16h.16X

276

PENELOPE J. BROTHERS

the carbenoid proton in non-porphyrin complexes is common. and it is surprising that despite the ring current effect of the porphyrin the carbenoid protons are still significantly deshieldcd. Several examples of carbene complexes have been structurally characterized (Fig. 5). and selected data for Ru(TPP)(=C(C02Et)2)(MeOH). Os(TTP)(=C(p-C~,HJMC)~)(THF), Os(TTP)(=CHSiMej)(THF), Os(TTP)(=SiEt,,THF)(THF) and a /I-carbido phthalocyanine complex, [Ru(Pc)(py)]$Z, are given in Table ,“,‘2~.l64.lh7.16X The ruthenium carbene complex has a Ru=C bond significantly shorter than those observed in the alkyl and aryl ruthenium porphyrin complexes. Ru(TPP)(=C(C02Et)l)(MeOH) and Os(TTP)(=C(/~-Cc,HIMe)l)(THF) show, as expected, planar geometry at the carbene carbon atom. and the bulky SiMej group in Os(TTP)(=CHSiMe3)(THF) results in an enlarged Os-C-Si angle of 142(2) The osmium silylene complex is an example of a base-stabilized silylenc, and shows a very short Os-Si bond and a long Si-O(THF) bond. The sum of the angles about silicon (involving osmium and the two ethyl groups) is 34X . indicating the silylene fragment is not planar but is significantly flattened relative to idealized s$ geometry (Fig. 5). I”’ The ruthenium and osmium carbene complexes are air sensitive, with the osmium silylene complex extremely so. The THF coordinated to silicon in the silylene complex can be displaced using pyridine. giving, for example. Os(TTP)= SiMel.py.‘“’ The silylene ligand itself is displaced by a carbene fragment when the silylene complex is treated with N$.YHCOIEt.‘“” The structurally characterized carbene complexes are six-coordinate. and exchange of the neutral THF ligand in the ruthenium and osmium carbenes by. for example, PPh3 or pyridine has been reported. The THF ligand can be removed in vacua and the five-coordinate conplexes observed in solution by NMR.‘“‘.‘“” Os(TTP)(=C(p-C,HIMe):)(THF) was unreactive toward a variety of regents (Mel, acetone, ethanol, silacyclopropane) but did react with pyridine N-oxide to give the diary1 ketone and Os(TTP)(==O)~.‘“” The osmium carbene complex Os(TTP)=CHCO,Et reacted with 4-picoline (4-pit) and other substituted pyridines to give ylide complexes. for example Os(TTP)(CHCO,Et. 4-pic)(4-pit) which contains two picoline groups. one bonded to the carbene carbon and the other directly to the osmium. There is a dramatic shift in the chemical shift of the OS-CH proton. from 2 I .6 ppm in the carbenc to -3.09 ppm in the ylide. Os(TTP)(=CHSiMe7)(4-pit) exists in equilibrium with the ylide Os(TTP)(CHSiMei+pic)(4-pit) in Cf,Dh containing 4-picoline again with a large chemical shift difference for the OS-CH proton (28.95 vs -4.82 ppm). The zwitterionic formulation for the ylide complex involves a formal positive charge on the 4-picoline nitrogen and a formal negative charge on the osmium center.‘“D The most significant and widely studied reactivity ofthe ruthenium and osmium porphyrin carbene complexes is their role in catalyzing both the decomposition of diazoesters to produce alkenes and the cyclopropanation ofalkencs by diazoesters. Ethyl diazoacetate is used to prepare the carbene complex Os(TTP)(=CHC02Et)

Transition Metal Porphyrin Complexes

277

from [Os(TTP)12, and it was noted that if excess N,CO,Et was used, the cis and ~TUIISalkenes Et02CCH=CHC02Et (maleate and fumarate esters. respectively) were produced in a 2: 16 ratio. Ihh This reaction is catalyzed by the osmium porphyrin dimer, the carbene complexes, and even the carbonyl and bis(pyridine) complexes Os(Por)(CO)(py) and Os(Por)(py)2, and was also reported for the ruthenimn porphyrin dimers (OEP and TTP) and the monomeric complex RulTMP).‘“’ All give L.;.T:~KIII.F ratios ranging from IS: I to 26: I. The coupling reactions were very fast (complete in seconds) for N$ZHCO:Et, but slower for N$Z(/>-ChHdMe)? and were not observed for N$HSiMe;. When the preformed carbene complexes Os(TTP)=CHSiMe3 or Os(TTP)=CAr? (Ar=p-C(,HIMe) were used as the catalysts with excess N2CHCO2Et. only the ethyldiazoacctate coupling products (maleate and fumarate) were observed, with no cross-coupling reactions. and the tinal osmium-containing products were the original carbene complexes. An osmium bis(carbene) complex has been proposed as a possible intermediate in these reactions, and one example, Os(TTP)(=CArz)? (Ar =p-C,HdMe), has been observed by NMR. with the carbene carbon observed at 305.5 ppm in the ‘jC NMR spectrum.‘“” The osmium carbene complex Os(TTP)=CHCO:Et is capable of both stoichiometrically and catalytically cyclopropanating styrene using ethyl diazoacetate. This is important because carbene intermediates are proposed but have not been directly observed for the many transition metal complexes which catalyze this reaction, while carbene complexes which achieve the stoichiometric reaction do not show catalytic activity. In the stoichiometric reaction. Os(TTP)=CHC02Et with excess styrene pave the cyclopropanc product in 73%’yield with an mti:s~tI ratio of I 1.5: I. Sample conditions for the catalytic process are [Os(TTP)j7 (I .7 /~mol), N2CHCO?Et (950 pmol) and styrcne (960 Irmol). giving an overall yield of cyclopropane with an m/i:.ry ratio of ca. IO: I .“” The osmium carbony1 porphyrin complex also acted as a catalyst for the reaction. The similarity of the product ratios for the stoichiomctric and catalyzed reactions were interpreted as evidence that the catalytic cycle involves a carbene complex. NMR evidence for the coordination of the styrene substrate to osmium was also reported. Other alkenes ((w- or /%methylstyrene. I-decene) were cyclopropanated. although with lower yields and stereoselectivities. Diphenylacetylene was doubly cyclopropanated (very rare) to give the bicyclobutane product.“” The osmium ylide complex Os(TTP)(CHCOzEt.4-pic)(4-pit) is also active for the ctoichiometric cycloproapanation of styrene. with a high crrlti:.qw ratio of 23: I, and is a potential model for metal diazoalkyl complexes proposed as intermediates in cycloproapanation reactions.“” Ruthenium porphyrin complexes are also active in cyclopropanation reactions, with both stoichiometric and catalytic carbene transfer reactions observed for Ru(TPP)(=C(COIEt)2) with styrene.‘“J Ru(Por)(CO) or Ru(TMP)(=O)z catalyzed the cyclopropanation of styrene with ethyldiazoacetate. with cu7ti:syn ratios of 13: I

278

PENELOPE

J. BROTHERS

for TPP but ca. 7: I for the more crowded TMP ligand. Like the osmium system. aryl alkenes and terminal alkenes are more reactive than alkyl or internal alkenes. Diazoalkane coupling reactions which give maleate and fumarate are observed in place of‘cyclopropanation when a less reactive alkene is used as the substrate.“’ Moderate enantiomeric excesses are observed when a chiral ruthenium porphyrin is used as the catalyst.‘7’m’7J A ruthenium carbene complex is presumed to be an intermediate, and when Ru(TMP)(CO) is used as the catalyst the carbene CH proton can be observed by ‘H NMR spectroscopy at 13.23 ppm.“’ Carbene intermediates have also been proposed in the ruthenium porphyrin-catalyzed insertion of the CHC02Et fragment into the N-H and S-H bonds of amines and thiols. “ji

D. Hydride and Dihydrogen

Complexes

A ruthenium porphyrin hydride complex was first prepared by protonation of the dianion. [Ru(TTP)]‘- in THF using benzoic acid or water as the proton source. The diamagnetic complex. formulated as the anionic Ru(II) hydride [ Ru(TTP)(H)(THF)]-, showed by ‘H NMR spectroscopy that the two faces of the porphyrin were not equivalent. and the hydride resonance appeared dramatically shifted upfield to -57.04 ppm. The hydride ligand in the osmium analogue reswith excess benzoic onates at -66.06 ppm.“’ Reaction of [Ru(TTP)(H)(THF)]acid led to loss of the hydride Ii&and and formation of Ru(TTP)(THF),. More details were elucidated by a study of the osmium OEP analogue. The anionic hydride [Os(OEP)(H)(THF)] (0‘-55.6) was protonated by benzoic acid to give 21 new complex containing two hydrogen atoms observed at (S -30.00 in the ‘H NMR spectrum. The deuterium substituted complex showed ‘JHr) = I2 Hz and T’ = I IO f 8 ms at 20 C. consistent with an rl’-H1 complex, Os(OEP)(H1)(THF). The dihydrogen ligand can be deprotonated using lithium diisopropylamide. The corresponding dihydrogen complex was more difficult to observe for ruthenium. although preparation of [Ru(OEP)(H)(THF)]from Ru(OEP)(THF)? with Hz and KOH was evidence for hydride formation through heterolytic activation of A ruthenium porphyrin dihydrogen an intermediate dihydrogen complex.““.“’ complex with a 2:1 Ru:H? ratio was observed using the cofacial diporphyrin Ru?(DPB), which coordinates the Hz ligand in the pocket between the two ruthcnium centers. “’ Osmium binds Hz more tightly than ruthenium. and as a result the osmium $-Hz complexes are more stable and more hydridic than their ruthenium counterparts. Variation of the a-donor ligand in the sixth-coordination site showed that stronger a-donors (imidazole derivatives) destabilize the Hz complexes relative to weaker a-donors such as THE The osmium Hl complex is more difficult to deprotonate than its ruthenium counterpart. requiring a stronger base to effect this (lithium diisopropylamide vs OH-). Considerable attention was paid to the ability of this system to achieve H/D exchange between Hz and D20 as this is

279

Transition Metal Porphyrin Complexes

an important

criterion

the anionic The

hydride

protonation

plex.

Rh(Por)H,

The dered bridge)

readily with

sterically cofacial

ands linked

with

which

in equilibrium

either

to release

contrasts

the isolectronic undergoes

by protonation rhodium

ruthenium

porphyrin

complex

Ru(DPAHM)

are extremely

/II~.YO position

reactive

complexes

are sufficiently

electron

deficient

vents

such as benzene

or toluene,

tion or ;IS solids.

In addition,

aromatic

hydride

Hz elimination,

complex

ot con-

and in fact

containing that

Ru(TMP)

(two

and cntnlyze

appear

HI/D?

slowly

and in the absence

a hinlig-

by an anthracene

14electron

they

and

trimesitylporphyrin

each porphyrin

on

the complexes

solvents,

or by oxidation.

[Rh(Por)12.‘X0

hindered

They

from

and the behavior porphyrin

bimolecular

H? and the dimer

the fourth

can be released

Hz is not bimolecular,

bisporphyrin through

deuterated

17’) Hydrogen

actvity.

[Ru(Por)(H)(THF)j-

reaction

IRu(Por)(H)] exists

for hydrogenase

Ru(ll)

to bind

exchange

centers.

aromatic

so-

in benrene

solu-

catalyze

exchange

of HJ into

of solvent,

exchange

01‘ D2 into

CHJ.‘“’

VI COBALT A. Overview There The

are two predominant

first comprises

where

R is a a-bonded

donor.

Most

on

cobalt

species

adenosyl

bond

of B~J, and interesting been directly

as

homolysis ;I result

initiates

(Por)Co(R)

organic

addressed

in a paper

relationship

energies by Halpern,

porphyrins

and L is il neutral

prior

in a-alkyl

coenzyme porphyrin

of continuing

functions complexes

interest, entitled

BI1‘?“‘X’ An exciting

has been their

cobalt

B12. Cobalt-

hydrogen-abstraction

intriguingly

studies

to the last decade.

interest with

in cobalt

in Vitamin

porphyrins.

and spectroscopic

of considerable

has been a focus

ligand

fragment,

established

the important

bond This

cobalt

or (Por)Co(R)(L).

were

close

for comparison.

for a-alkyl

cobalt

complexes dcvclopmcnts

A source

Co-C

types fororganometallic

or other

synthetic

has been their

not USC the porphyrin

opment

aryl,

and -arylporphyrins

been reviewed.5.7.x

porphyrin

n;lturc

alkyl,

of the important

a-alkyl

and have

structural

S- or e-coordinate

“Why recent

use as clltalysts

;Irc

and has does devcl-

for the free

radical living polymerization of alkenes. The second structural type found for organometallic cobalt porphyrins contains an organic fragment bridged between the cobalt and one pyrrolic nitrogen. Cobalt complexes

of N-alkyl-

or N-arylporphyrins

specifically

addressed

here). The bridged

the N-alkyl

group

also forms

a a-bond

arc well complexes

to cobalt.

They

established

(but will

are derivatives are also related

not be

of these where to the axially

280

PENELOPE J. BROTHERS

symmetric

carbene

complexes

sense that a carbene M(Por)

either

a-bonds.

by forming

on iron porphyrins,

a double

served,

although

complex porphyrin

migration

oxidation.

carbene

ligand

covered

in previous

only

of a a-bonded

review

contain

where

form

containing

triggered

also

by

developments theoretical

symmetric

iron

carbencs.

despite

transition

In

is ob-

a Co, N-bridged

and early

ago,

porphyrin

in the chemistry

oxidation species.

of carbene

from Co to N is

two

in the section

one-electron

an interesting

of the axially

d”. first-row

As discussed

complexes

including

cobalt(II1)

developments

arc

analysis

porphyrin

car-

the fact that both

metals.5.7.x The last decade of Co,N-bridged

has

organometallic

species.

The chemistry

of organorhodium

dressed

in

iridium)

porphyrins

separate

a

and the M(II1) a monomer,

section. centers

hydrides,

porphyrin

and -iridium

Much

around

M(Por)H.

chemistry,

where

and the hydride

dence for the existence

Neither the Co(I1)

Co(Por)H

of Co(Por)H

B. Cobalt a-Bonded

a-alkyl

of the Co(II1)

or from

the Co(I)

of these species porphyrin

dimers, Co(Por)

in

exists

but never directly are providing

intermediate

(and

[ M(Por)]l.

has :I counterpart

complex

has been implicated

will be ad-

of rhodium

of the M(II)

recent developments as a likely

derivatives

chemistry

in a variety

;I\

ob-

firmer

e\,i-

of reactions.

Alkyl and Aryl Complexes

or a-aryl

reaction

porphyrin

of the exciting the reactivity

served. This is still the case, although

Cobalt

to the metal or by forming

the bridging

over 25 years

articles.

in the

fragment

of the Fe,N-bridged

ligand

porphyrin

the occurrence

types of complexes porphyrin

chemistry,

and osmium

metalloporphyrin

a

nitrogen.

formation

Cobalt

benes vs the CoNbridged seen continuing

bond

pyrrole

a

induces

were first reported

that rationalizes

cobalt

(n + r)

ruthenium,

with

the two can be interconverted.

(and nickel)

one-electron

for iron,

CR?, can interact

one to the metal and one to

of an iron vinylidene cobalt

observed

fragment,

porphyrin

complexes

are generally

prepared

either

by

halides

anions

Co(Por)X with organolithium or Grignard reagents. with alkyl or aryl halides. a-Aryl complexes [Co(Por)]

are best prepared by the former method, utilizing a Co(II1) prccursor.s.7.x A practical drawback to the use of organolithium and Grignard reagents is their air and moisture sensitivity. Alkylation of Co(TPP)CI to produce Co(TPP)R using SnRl (R = Me, Et, i-Pr, rz-Bu) or one of a selection bis(dimcthylglyoximato) new methods species

or bipyridyl

for preparing

o-bonded

and will be discussed

ligands

of organocobalt avoids

complexes

complexes

this problem.‘x3 involve

intermediate

containing Several other Co(Por)H

in that section.

An attempt to lithiate the Co-bonded aryl ring in Co(TPP)@ChH,Br) by reaction with n-BuLi led instead to exchange of the aryl group for the butyl group. This reaction is more general, and a range giving Co(TPP)Bu as the product.‘XJ of Co(TPP)R

complexes

containing

aryl, alkyl,

styryl,

and alkynyl

groups,

when

Transition Metal Porphyrin Complexes

281

with organolithium compounds at -78 C, led either to rapid substitution of R or to an equilibrium mixture of products. Similar, but slower, exchange is observed with Grignard reagents. The process is postulated to proceed by attack of the carbanion R’- on the substrate to give an intermediate “ate” complex 01 low stability, [Co(TPP)RR’]-, which then loses whichever of R or R’ is the better leaving group. The relative leaving group ability of R and R’ determines whether complete exchange or an equilibrium mixture is observed. Evidence for the “ate” complex comes from ‘H NMR observation of [Co(TPP)(C-CPh)?jproduced when R and R’ are both alkynyl. The much reduced rrrrr7s effect of alkynyl groups (relative to simple aryl or alkyl groups) accounts for the reduced lability of this complex, which is stable in solution at 20 C.“’ Very recently, a series of trihalomcthyl cobalt porphyrin complexes Co(OEP)CX; was prepared either by the reaction of Co(OEP) with CBrCl+ CBr4 or Cl,, or by the reaction of [Co(OEP)]- with CC& or CBr+ The dihalomethyl complexes, formed in small amounts in these reactions, wcrc prepared in larger amounts from [Co(OEP)j- with CHX+‘XS In a similar fashion, R$nH reacted with Co(0EP)CI-I; or Co(OEP) to give Co(OEP)SnRx and CHq or Hl, respectively. Stannyl complexes were also prepared from R$nCI with (Co(OEP)]- (R = /r-Bu, Ph). An X-ray crystal structure of Co(OEP)SnPh3 confirmed its five-coordinate nature and exhibited a CopSn bond length of 2.5 I O(2) A (Fig. 6). This complex is very thermally stable and moderately air stable, and reacts with 12 to give Co(OEP)I and ISnPh3.‘x’ An treated

(4

(W

FIG. 6. Molecular structure\ or sclectcd organonletattic cobalt (a) Co(OEP)CH~,“”

(h) C’O(OEP)(CH~)(py).‘“”

CC) C0(TPP)CH2CH0.‘XX

porphyrin complexrs: cd) Co(OEP)SrlPh;.‘X’

PENELOPE J. BROTHERS

282 attempt

to prepare

with Me$iCI phosphoryl Two

a cobalt

in HMPA complex,

recent

N2C(C02Me)2 Co(Por)Br

give a derivative

by the reaction

to the unexpected

of &N-bridged

carbene

of [C~(OEP)(OH,)]CIOJ

(Eq. (5)). Different (Por

silyl complex

led instcad

of ICo(TPP)j-

Formation

of a cobalt

Co(TPP)P(O)(NMe,)2.“”

examples

from the reactions

porphyrin

solvent

reactivity

= OEP or TPP). which containing

complexes

have been prepared

with the diazoalkanes

N2CHSiMe3

is seen for the Co(lll)

reacts, t’or example.

halide

and

complex

with N2C(C02Me)2

a Co-0-C(OMe)=C(COJMe)-N

bridged

to

complex

(Eq. (6)).““.‘“’

(5) OMe 0

Only

LI small

phyrin in Table been

number

complexes V.“‘.“’

have

01‘ structurally

characterized

been reported.

and selected

In a recent

probed

by

Co(OEP)(CHj)(py),

the Co-N(py) plexes ofthe recorded.

of

structural the

and Co(OEP)(py).

2.0 18( 12) r\, respectively. the six-coordinate

study.

;I comparison

distance

fcaturcs

molecular

This

in this complex

type Co(Por)(X)(py),

bond

(2.2 14(c)) A) longer methyl

Co-N

ofthcir

normal

to the porphyrin ring current effect. The extent ot‘the upfield the distance of the nucleus in question from the macrocycle, ligands, the largest a-protons exhibiting complexes anomalous

distances

complexes have been discussed structures RI 2. ‘W Representative

diamagnetic

upfield

in

with

than that in other conlongest

NMR

observed

and

are longer

influence,

axial

arc usually

have

are I .973(h)

bonds

base-oft’ and base-on models of coenryme cobalt alkyl complexes arc shown in Fig. 6. In diamagnetic porphyrin complexes the ‘H and ‘jC ligands

bond

Co(OEP)CH3,

to the t,ur~

and in fact is one ofthe

The live- and six-coordinate

of

lengths

pot-=

are collected

of the Co-C

and Co-N(py)

has been attributed

cobalt

for these

structures

The Co-C

and both the Co-C

complex.

organometallic data

chemical

shifts position

as of fordue

shift usually reelects so for r?-alkyl axial

uptield shift is ohscrved in the order (a > p > y, with the the largest upfield shift. This is observed for simple rl-alkyl

of Rh(lIl) porphyrins. for example, but cobalt n-alkyl porphyrins arc with the a-proton resonance broadened and appearing downfield of the

Transition Metal Porphyrin Complexes

283

M-C Bond LUlgthiA m -Ronded complexes Co(TPP)CH2CH0 Co(0EPK.H;” co(OEPKl~~(‘rl7 C‘o(OEP)(CH;)(py) WTPP)CH2U0)CH; WOEC)Ph ICo(OEC)Ph](‘lO, Ni(TPP){/r-(Ni.N)-CHCOzEt} Stflrzrlyl c011zplex Co(Ol:P)SnPll,

?.OX(3) I .937(3) I .970(7) 1.005(1)

I .938(1) I .X56(3) I .X-t’)ts) I .o I h( 3 )”

co-Sn. 2.510(2)

I .966(5 1

0. I4 O.OW(3) 0.105(3) 0. IO1 co-c-c. I l4.?5lIJ) 0.00x ( IO\Lard p) I 0. I I 0. I x5 0. IfIS 0.1’) Ni.. .N. 2.010(3) k 0.077

b-protons. Various reasons have been proposed for this phenomenon, including a suggestion that an agostic interaction between cobalt and the fi-hydrogens brings them into closer proximity to the porphyrin. and hence upfield of the a-protons.‘“’ A more detailed analysis finds that this is not the case,“’ based in part on an X-ray structure of Co(OEP)CH&JHj which exhibits a Co-C bond of I .988(2) (very similar to that observed for Co(OEP)CH3’““) and a Co-C-C angle of 1 14.25( 14) , inconsistent with a Co-b-H agostic interaction.l”’ The broadening of the a-proton resonance in the ‘H NMR spectrum and reversal of its position relative to the b-protons is attributed to coupling to the quadrupolar ‘“Co nucleus (I = 7/2), and a paramagnetic contact shift arising from a low-lying triplet state. In Co(OEP)CHj the methyl resonance exhibits anti-Curie behavior. consistent with a contact shift mechanism. Coordination of pyridine to Co(Por)(/z-alkyl) complexes causes the w-protons to shift upfield and the p-protons to shift downfield. The pyridine ligand increases the energy difference between the ground state and the low-lying triplet state and decreases the size of the contact shifts.‘“’

Investigations of the cobalt-carbon bond energies in organometallic cobalt porphyrins continue to attract interest, originally because of their similarity to coenzyme B 12,and more recently because of their role in the catalysis of free radical

IXX IO0 192 IO0 IX9 201 701 2X8 IX5

284

PENELOPE J. BROTHERS

living polymerization of alkcnca. Bond energies have been measured from both kinetic and thermodynamic (equilibrium) studies. In the kinetic method. rates ol Co-C bond homolysis are measured usin g TEMPO as a radical trap. The kinetic data can be used to calculate the Co-C bond energy atter allowing for the diffusioncontrolled Co-C recombination reaction (Eqs. (7) and (8) and the rate expression in Eq. (Y)).‘“’ One particular study used this method to investigate the effect on the Co-C bond energy in Co(OEP)(CH,Ph)(PRj) by varying the pK,, and size Co’n(Por)R 5

R. + TEMPO L

k

Co”(Por) + R.

(7)

R-TEMPO

(8)

k, k:[TEMPO] (“x = kk,[Co(Por)R] + kl[TEMPO]

(9)

(cone angle) ofthe phosphine ligand. PR;. Ix2 The reason for this is that the vitamin Blz coenzyme contains a cobalt corrin complex. in which the puckered con-in ring. although closely related to a porphyrin, can adopt variable conformations. These changes in conformation affect the Co-C bond energy for the Co-5’-adenosyl group. and can trigger Co-C bond homolysis. Variation ofthe steric and electronic properties of the phosphine ligand in the cobalt porphyrin study modeled this process. The Co-C bond energies (in the range 24-30 kcal mol-‘) wcrc found to be dependent on the phosphine pKi, values but independent of the size of the phosphine ligands. It was proposed that the porphyrin ligand is not sufficiently flexible. relative to a corrin. to transmit the steric effect of the bulky axial ligand to the Co-C bond. In other words. the porphyrin acts as a rigid barrier shielding the Co-CH?Ph group from steric perturbations, and this has been postulated as ;I reason nature does not use the porphyrin ring in vitamin BI~.‘~~ The importance of steric effects in vitamin Bl, was further supported by a vibrational study on a series of complexes Co(Por)R, where Por = OEP. TPP or TMP. and R = CHj ot CD?. FT Raman data for VC+C showed an isotopic shift for each pair ofCH?/CD: complexes of ca. 30 cm-‘. For Co(OEP)CH3 and Co(TPP)CH3, UC~,-~was very similar (ca. SO0 cm ‘) but for the much more crowded Co(TMP)CHx a big shift to lower energy. with v~+-(‘ = 459 cm --I, illustrating the steric effects on the Co--C bond. ‘W NMR line broadening is a suitable kinetic method for determining activation parameters for Co-C bond homolysis. and gave AH’ values in the range 1% 22.5 kcal mol-’ tor ’ a selection of Co(Por)R complexes containing secondary ot tertiary alkyl groups.‘“’ Bond dissociation enthalpies and entropies for several

Transition Metal Porphyrin Complexes

285

complexes Co(Por)R and their singly oxidized products [Co(Por)R]+ (formed by chemical oxidation) were studied in a stopped flow kinetic study. The Co--C bonds in the oxidized products are weaker than in the neutral complexes.‘“” Equilibrium studies on Co-C bond dissociation energetics were investigated through a study on the reactions of the cobalt(ll) radical complex Co(TAP). with organic radicals, C(CH3)(R)CN, in the presence ofalkenes. Fast abstraction of H. from the organic radicals by Co(TAP). formed an intermediate hydride Co(TAP)H (not observed) which added rapidly to alkenes to form organocobalt complexes. Equilibrium concentrations of the solution species present once the organic radical species had achieved steady-state concentrations allowed evaluation of the equilibrium constants for Co-C bond homolysis. For example, AH values for Co-C bond homolysis in (TAP)Co-C(CH&CN and (TAP)Co-CH(CH3)ChH5 were determined directly by this method to be 17.8 i 0.5 and 19.6 & (1.6 kcal IllOl -‘, respectively. The value for (TAP)&--C~HO was measured indirectly by competition studies and found to be 30.9 kcal mol ‘. I’)’ In tertns of relative Co-C bond energies, those in the trihalomethyl complexes Co(OEP)CX3 arc observed to be qualitatively weaker than in Co-alkyl porphyrin complexes. The high thermal stability of the cobalt porphyrin stannyl complexes was interpreted as an indication that, surprisingly, the Co-Sn bond is stronger than the Co-C bond in Co(Por)(alkyl) complexes.‘x5

Organocobalt porphyrin complexes have been investigated by electrochemi%try, and earlier studies are summarized in review articles.7.x Briefly, oxidation of Co(Por)R led to migration of R from cobalt to a porphyrin nitrogen atom, giving a Co(II) complex of an N-alkyl porphyrin, [Co(Por-N-R)]t.‘“X Reduction led to [Co(Por)] or [Co(Por)R] , with the exact nature of the product dependent on the solvent, the scan rate, and the nature of R. In more recent developments. the initial site of electron transfer was elucidated in an electrochemical study on Co(TPP)R (R = CHj, C~HS or CHCI,) and Co(TPP)(ClH5)(py). Each complex undergoes up to two reductions and two oxidations, each of which occurs at the porphyrin n-system rather than at the cobalt center. giving Co(II1) porphyrin anions and cations. respectively.‘“’ The oxidation ofCo(TPP)R and Co(TPP)(R)(L) (R = CH;, CIHS. CJH~ or CbH5; L = MeCN or a substituted pyridine) was investigated in more detail.‘“” One- or two-electron oxidation of the cobalt complexes was achieved using [Fe(phen)3]3’ as the oxidant. and the products of the initial oxidation were characterized by EPR and electronic spectroscopy and stopped-flow kinetics. The initial singly oxidized products have some d5 Co(W) character for the six-coordinate complexes [Co(TPP)(R)(L)]+, while the five-coordinate complexes [Co(TPP)R]+ are best described as Co(llI) porphyrin r-cation radicals. After

286

PENELOPE

two-electron phyrin

initial

nitrogen

product

oxidation,

Chemical

migration

is observed.

was the Co(III)

of the R group

and the kinetics

N-substituted of vinyl-

from

of this process

porphyrin

or aryl-cobalt

complex

cobalt

measured.

to a porThe

[ Co(TPP-N-R)

by [ ArjN.

]’ to

was investigated

and aryl groups

ing that both the Co-to-N

porphyrins.

Losing chiral

and the reverse

for example

final

]?+, I”’

[SbCl6] -. also inducts the migration of the o-bonded group from cobalt nitrogen.“” The stereochemistry of the reversible metal-to-nitrogen transfer alkyl

oxidation

J. BROTHERS

cobalt(lII)

migrations

porphyrins.

take place

of

indicat-

by intramolecular

routes.‘“” A transient

Co(IV)

aryl migration reported

species

process.

(and indeed

corrole

bond

two cu-pyrrolic

form.

is more effective

states. Recently

prepared

atoms

corrole

contains

Co(OEC) using

with

Co(IV).

was prepared

PhMgBr.

aqueous

iron

neatly

plane

The by a

charge

in its

high oxidation

;I number

Co(OEC)Ph.

of uw which

of the Co(Il1)

complex

was further oxidized in CH$ZIz as the oxidant. giving [Co(OEC)Ph]CIOa

solution

and [Co(OEC)Ph]+, exist

show

complex

01

replaced

Co(OEC)Ph

perchlorate

into the corrole

Both complexes

complexes

by the reaction

was tnore stable than its neutral precursor. plexes were determined. and show Co-C A for Co(OEC)Ph

are known).

at stabilizing

(OEC)

alkyl

have not been

a ?-

and bearing

than a porphyrin

usual features. X’ The cobalt octaethylcorrolc formally

complexes

but with one /Iz(J.so-carbon

carbon

organocobalt

in the Co-to-N

porphyrin

Co( IV) complexes

to a porphyrin

similar

between

deprotonated

to bc important

stable Co(lV)

few stable non-porphyrin

macrocycle.

direct

is believed

although

The molecular bond

in the oxidiLcd

in the solid

lengths

~espectivcly.

state as X-K

complex. dimers

structures of I .937(j)

The with with

cobalt shorter

which

of both comand atom

I .970(7) tits more

Co-N

the two corrole

bonds. planes

ca. 3.5 A apart. EPR data and magnetic measurements indicate that Co(OEC)Ph can be described as a d” Co(W) complex. with one mnpaired electron in a tl orbital oriented

toward

the corrole

r-cation

radical

character.

plex

in which

unusual

NMR

Co(TPP)

the corrole behavior,

the complex

some

was formulated

as a Co( 111) conand as such exhibits

is doubly

oxidized.

Co(II1)

corrole

a paramagnetic ring current.“” to act as ;I catalyst for the electrocarboxylation

as intermediates (the latter detected by spectroscopy) in the of free R or R., which then reacted directly with CO?.202.203

precipitated of organic

giving

and butyl bromide with CO?. to give PhCH2C(O)OCH2Ph and respectively. The proposed mechanism involved Co(TPP)R

and [Co(TPP-N-R)]+ catalytic production nation

macrocyclc including

has been demonstrated

of benzyl chloride BuOC(O)C(O)OBu.

Co(TPP)

nitrogens.

[ Co(OEC)Ph]CIOa

on graphite

halides,

including

foil has been successfully used for the determiDDT and I ,3-,3,4,5,6-hexachlorocyclohexane

(lindane). to sub-ppm level in aqueous solution. Deoxygenation of the solutions is not required. and the technique is moderately insensitive to the ionic composition 204 of the solution.

Transition Metal Porphyrin Complexes

C. The Search for Cobalt Porphyrin In contrast a central

to the rhodium

role in many

Hydride Complexes

porphyrin

hydride

of the important

istry. the corresponding as reaction

cobalt

intermediates

287

complexes,

developtnents

porphyrin

in a variety

hydride

Rh(Por)H,

in rhodium complexes

of’ processes,

which

porphyrin

play chen-

have been itnplicated

but a stable,

isolable

exatnple

has yet to be achieved. Cobult( trolled

II) complexes

potential

porphyrin posited

electrolytic

complexes as filtns

production

reaction

transfer

a variety

of’H20

directly water

Reduction

two

Co(Por)H

units.

The

or were dewas followed

intermediate.

Although

problems

carbon.

to [Co(Por)]-

of’ Him on Co(Por)H.

practical

Ihr the con-

acid solution.

on glassy

to give the hydride

by attack

was demonstrated,

are catalysts

to H1 in aqueous

adsorbed

of methods.

with

either

requiring

porphyrins

Hydrogen

or by a disproportionthe overall

including

lcasibility

of’

the rate of’ electron

still riced to bc ovet-cotne.205.~0”

Co(OEP)

reacted

benr.enelmethanol

with

process

ucts were generated. ;I secondary

nlkyl

celerated

was proposed t-c&chemistry

with

resulted highly

by the addition

of

an

the Co-C

bond

alkenes

through

be explained

(R = Ph or

alhylcobalt

and 7,-heptene

at the ?-position.

an intermediate

hydroperoxide. hydride,

of the stability

prod-

each gave

and cyclopen-

and -cyclohexyl

products.

did not rcuct. The reactions

such as r-butyl

in terms

in oxygenated

R)=CH,

alkync.

I-pcntcnc.

in the cobalt-cyclopentyl oxidant

or I -hexync

Co(OEP)C(

in place of’thc

I -hexene,

substituted

to proceed could

complexes

usin g an alkene

complex

More

and phcnylacetylene

the \ inyl

For example.

and cyclohexene

rcspcctivoly.

NaBHl

lo give

Bu). In a similar

tent

either

reaction

then occurs

this process

reduction

wcrc

using

hy a nucleophilic ation

of three water-soluble

were ;IC-

The reaction

Co(OEP)H, of‘ the organic

and the radicals

c
competing

elimination

an unsaturated

molecule

of’ H?.“”

The transient

(as above)

cobalt

or. altcrnativcly,

hydride

c;ttt formally

the hydride

can

react

288 with

PENELOPE an organic

substrate

product.

Several

the sane

conditions

by hydrogen

(using

14 for the case where NaBH+

Co(OEP).

OCH(Me)CHO droperoxide

is added.

from a variety ilarity

to generate

ofaldehydea.

Although

with

alkene.

ofacyl

generated

radicals

conditions

In the above strates

with

in a radical

by the reaction

from

AIBN

or VAZO-S2.“‘.“’

ical and an alkene, CO(TAP)CH(CHJ)X

through

intermediate.

hy-

cleanly

overall

sim-

it has been Co(OEP)H,

by Co(OEP)

trapping

with the aldehydes.“‘“.~”

to achieve

These

the intramolecular

with

tertiary

commercially

CH?=CHX,

then

cycliza-

organic

or alkyne,

by NaBHJ

with

as the source radicals.

diazo

Co(TAP) HC=CX

or Co(TAP)C(X)=CH?,

reacted

organic

by H.. An alternative

radicals

available

In chloroform,

was generated

which attack

is to use organic

of Co(TAP)

produced

is produced

have an apparent

Co(OEP)H

precursor.

mechanism

selves

abstraction If t-butyl

that a hydride of‘t-BuO.

the transient

porphyrin

of Co(Por)H

hydrogen radicals.

are produced

are

an alkene.“”

examples

of a Co(lIl)

generation

from reaction

products

ether substrates,

products)

under

as shown

and Co(OEP)

and cyclic

have also been exploited

tion of an aldehyde

duction

these reactions

that in the cast of’the aldehydes The ucyl (and other

nonselective

Co(OEP)C(O)R

alkync.

is not involved. reaction

from

three

(33%).

and a-(f’ormyl)alkyl

then the acyl product

to the reactions

concluded

acyl

oxidant)

as the substrate.

Co(OEP)CH(Me)CHO

(I 9%) (Eq. ( IO)), arising

the aldehyde

a new organocobalt were metallated

Oz. or an added 20X is the substrate.

THF

(I 8%).

ethers

NaBHI.

01, and propanal

Co(OEP)C(O)Et

to form

ring cyclic

Co(OEP).

With

from

elimination

five- and six-membered

in Scheme observed,

J. BROTHERS

reacts

with

to give alkyl

respectively.

method

fol

of’ the hydride.

C(Me)(R)CN.

radical

resub-

them-

initiators

such

the organic or vinyl

Reactions

as rad-

products,

ol‘Co(TAP)

and C(Me)&?N with either alkyl halide or epoxide substrates occurred in DMF, giving alkyl or 2-hydroxyalkyl products. The reactions were conveniently t’ollowed by ‘H NMR spectroscopy, observing tion of’ the organocobalt(II1) products. This the preparation Co(OEP), synthesis,""

of over

Co(TMP), 1.2”

The products

33 organocobah

and cobalt

of the above

derivatives.

phthalocyanine,

reactions

the loss of’ Co(TAP) and l’ormaprocess, which was exploited fol and which

has been dubbed

are consistent

with

also

work\

“tertiary

Markovnikov

for

radical addition

of’ transient Co(Por)H to the unsaturated alkene or alkyne substrate. The regiochemistry is determined by formation of the most stable organic radical. which

289

Transition Metal Porphyrin Complexes

tends to produce secondary rather than primary alkyls, and thus the products are kinetically rather than thermodynamically favored. The rate of the reaction with alkenes matched the rate of radical production from the initiator. Yields were quantitative for very stable organocobalt products like Co(Por)CH(Me)CN or Co(Por)CH(Me)COzEt formed from acrylonitrile or ethyl acrylate, respectively. Yields dropped as the Co-C bond strength decreased as a result of competition with Co-C bond homolysis. For alkyne substrates, the kinetic product forms at short reaction times or low temperatures, with the thermodynamic product appearing after longer times (Eq. (I I)). For example, HC=CCH20H initially gives Co(TAP)C(CHzOH)=CH:. with CoCH(Me)CHO appearing at longer times as the result of a 13hydrogen shift and keto-enol tautomerization.

(II)

The corresponding reactions oftransient Co(OEP)H with alkyl halides and epoxides in DMF has been proposed to proceed by an ionic rather than a radical mechanism. with loss of H- from Co(OEP)H to give [Co(TAP)I-, and products arising from nucleophilic attack on the substrates.“‘.“’ Overall, a general kinetic model for the reaction of cobalt porphyrins with alkenes under free radical conditions has been developed.“3 Cobalt porphyrin hydride complexes are also important as intermediates in the cobalt porphyrin-catalyzed chain transfer polymerization of alkenes (see below). D. Cobalt Porphyrins

as Catalysts

for the Polymerization

of Alkenes

The definition of a living polymerization process is one where each polymer unit contains an active site where chain growth occurs indefinitely without termnation or chain transfer reactions. Living radical polymerization can be achieved using a combination of one radical that initiates polymerization, and a second that binds reversibly to the growing polymer radical. The use of Co(TMP)R to initiate and control the polymerization of acrylates to form hompolymers and block copolymers was first reported in 1994.““.“5 Indications of a living radical polymerization process were a linear increase in the number average molecular weight with monomer conversion, and relatively small polydispersities. Co(TMP)CH2CMe3 or Co(TMP)CH(Me)COzMe were used to initiate the formation of polymethylacrylate at 60 C in benzene under argon, with a ratio of methyl acrylate monomer

290

PENELOPE J. BROTHERS Co(TMP)R

-

Co(TMP).

R. + CH&ZIIX

-+

+ R.

RCH>CHX.

RCH>CHX.

+ Co(TMP)-

e

RCH2CHXCo(TMP)

RCH2CHX.

+ (n + I)CHr=CHX

3 RCH~CHX(CHzCHXKII,CHX

RCHfZHX(CHLZHX),CH~CHX.

+ Co(TMP)

s

C11~CIIX(CH~CHX),CH~CHXCo(TMP)

S<‘HI:\II.

to cobalt

porphyrin

formation

of Co(TMP){

of 2500: 1. When

2. etc., was observed process

is shown

reversibly

hy ‘H NMR

is not fully

living.

is self-rcgulatin

Cobalt

Co(Por)H.

then initiates

was limited

to 50: I, sequential

atom from

a growing atom

a new propagating R is the polymer

polymer

+ CH?=C(

termination

transfer

+ Mc)X +

+ (11 + l)(CH2=C(Me)X)

chain.

which

the proces\

events

transfer

catalysis

radical.

do occur.

catalysis occurs

of the

by abstrac-

in this case by Co(Por) to ;L new monomet-,

The reaction

X is CN),

for this

effect.““.“’

in the chain

poly’ner

chain.

Although

radical

is then transferred

+ .C(R)(Mc)X

(Por)CoH

is Co(TMP).

Chain

II = 0. I,

sequence

is R. and the radical

radical

are involved

reaction

radical

the persistent

ofacrylates.

units with

The

chain

some bimolecular

complexes

(Por)Co

C(Me)?X

polymer

The hydrogen

Eqs. 12 (where

spectroscopy.

g through

polymerization

tion of a hydrogen form

because

porphyrin

ratio

IS. The initiating

to the growing

the system free-radical

this

CH(C02Me)CH~},,CH(C02Me)CH~

in Scheme

binds

l-5.

to

which

steps are shown

in

( 13). and ( 14).‘”

(PorKoH --, (Por)Co

+ CH?=C(R)X

(12)

+ C(Me)?X

(13)

X(Me),C(CHlC(Me)X),,CH2C(Me)X. ( 14)

This ration

is closely

related

of orgmocobalt

to the “tertiary porphyrins.

radical

in which

of Co(Por)H instead of creating a new radical form a tertiary cobalt alkyl then polymerization is observed.“‘.“’

The

in part by competition chain transfer catalysis

kinetics

synthesis”

alkenes

for this process

insert

scheme

for the prepa-

into the Co-H

bond

as in Ey. ( I?). If the alkene would rather than cobalt-alkyl formation have been

investigated

studies involving two different alkenes. process, where two alkenes (monomer

in detail.

This mimics and oligomers

the OI

291

Transition Metal Porphyrin Complexes

the alkene ing

formed

deuterated

from

methyl

than 3. indicating the catalytic

the radical methacrylate-(18

that hydrogen

cycle.“”

on the degree

are present.‘”

showed

atom

transfer

The dependence

of polymerization

f‘cr polymerization

initiator)

a kinetic occurs

methacrylate

isotope

studies

eff’ect

propagation

us-

greater

in the rate-limiting

of’ free-radical

in the cobalt

of methyl

Isotope

step of’

rate constants

porphyrin-catalyzed

chain

and methacrylonitrile

has

trans-

also

been

investigated.“’

E. Reactions The

of Cobalt(lll)

interaction

19X6. with cluding

of’ alkynes

the reaction

ethyne

reactions

were

N-C(R)=C(R)-N

an

with

niacrocycle.“x cationic

cobalt

workup

bearing

between that time.

containin

gave

substituent

Co(OEP)-CH=CH-N-(0EP)H apparently

disparate

TPor = OEP or TPP). brown

to green

IJV-visible porphyrin excess formally

ethyne cthyne

reactions

This reaction

and is reversible,

spectroscopy.

Co(lII)

These

adduct.

showed

of alkynes in CH2CII between

FeCIj

complex

followed

by

as its HC104

in CHICI?, Reaction

I’ollowed

by

the HCIO, ligand

aalt),

;I

an

vinyl

words

by a closer

by a color behavior

suggested

a

change when

of the adduct with

had sonic

invcsti-

and ethyne from

f’ollowed

the formation

to be paramagnetic,

[Co(Por)(H,0)2]+

in other

[Co(Por)(H20)2]C101

isosbcstic

spectroscopy

with

gave

on cobalt.“’

was accompanied

observations

’

of’ ethyne

in CH$Zl2

be tied together

can

in the por-

[Co(OEP)-CH=CH-N(C7HU)1

between

showing

‘H NMR

the complex

precursor

with

OEP

as the axial

of the interaction

atoms

(R = C02Mc)

of’ this complex

(a

N-vinyl-OEP

prod-

containing

Co-C(R)=C(R)-N,

and [ Co(OEP)(H~0)21CI04

containing of the nature

RC=CR

on the p-carbon.“’

of’H,(OEP)

in in-

unravclled.

to [Co(OEP)(H~O):]CIO~

complex These

nitrogen

bridge,

complex

The ultimate

of’ the interactions

have been gradually

vinyl

reported

of alkynes.

porphyrins.

adjacent

with

first

a series

as oxidant.

the N”,N”-etheno-bridged

of ethyne

mixture

was

with

the details

Oxidation

complex

(ration

two

g an etheno

the cationic

gave

a pyridinium

cquimolar

bridge

nitrogen.

Addition

2.6lutidine.

porphyrins

of Fe(C104)3

of [Co(OEP)(H20)1]CI04

and a pyrrolic

and Alkynes

the N~‘.N”-ctlieno-bridged

porphyrins

gave a product

an acidic \alt~““.“ll

cobalt(lII)

Since

cobalt(lI1)

The reaction rapidly

with

with Alkenes

of ICo(OEP)(H20)2]CIO~

itself’, in the presence

uct~ of’ these phyrin

Porphyrins

by

of’ a cobalt

in the presence

C, symmetry.“’

Co(II)

red-

porphyrin

01‘ The

radical

cation character. Two possible structures can bc proposed for the ethync adduct: ;I Co(Il) porphyrin radical cation rr-ethyne complex and a Co( III) complex containing

a cationic

to nucleophilic N-etheno-bridged

rr-vinyl

ligand.

The P-carbon

atom

in the latter

attack. Intramolecular attack by a pyrrolic product. while intermolecular attack by

nitrogen ;I nitrogen

form

is subject

the Co. nuclcophile,

gave

292

PENELOPE J. BROTHERS

HC=CH

r

HCFCH

I :H

-!

either 2.6-lutidine or a free-base porphyrin, gave the cobalt-vinyl-pyridinium and Co.N-etheno-bridged bisporphyrin, respectively. These reactions are summarized in Scheme I 6.223 The OEP and TPP complexes show some difTerences in reactivity. Reaction of ethync with [C~(TPP)(H~O),]CIOJ in CHzC12. followed by addition of aqueous NaX (X = Cl. SCN) gave the biscobalt(ll) hisporphyrin XCo(TPP-N-CH=CH-N-TPP)CoX, which could be demetallated to give freebase N,N’-etheno-linked bisporphyrin (Scheme 16).“‘.“3 Further reaction of the free-base bisporphyrin with [Co(Por)(H10)2]+ and ethync gave tri- and tetraporphyrins, (Por)Co-R-(NPorN)-R-(NPor) and (Por)Co-R-(NPorN)-R-(NPorN)R-Co(Por), where each -R- group is a -CH=CHetheno bridge, and (NPorN) is a porphyrin linked through two adjacent nitrogens to an etheno bridge. The different reactivity of OEP and TPP could be exploited to create different combinations of home- and heteroporphyrin oligomers. Oxidatively induced Co-to-N migration of the vinyl group can produce further variations in the bridge linkages.“’ The hetero-bisporphyrin complexes containing one cobalt and one fret-base porphyrin display switching of the cobalt between the two porphyrin ligands during the course of den~etallation/n~ctallation sequences, and the transformation 01‘an

Transition Metal Porphyrin Complexes

293

asymmetric, unsaturated N-CH=C--N”‘,N” linkage to a symmetric, saturated N”.N”-CH-CH--N”‘,N”” ,’In k,age was determined from an X-ray crystal structure of the free-base bisporphyrin containing the latter bridge.“’ The electronic structure of’cobalt(lll) porphyrins depends on the nature of the axial ligand and the solvent. The simple halide complexes Co(Por)X are diamagnetic cl” Co(lII) complexes in both methanol and CH$ZI~. However, the aqua complex is also ;I diamagnetic d” Co(II1) species in methanol, but in CH$ZI? the axial ligands are lost and the species is best formulated as a (1’Co(I1) porphyrin n-cation radical.“” As described above, [Co(Por)(H,0)2] ’ in C’H$ZII reacts with substituted ethynes, RC=CR, via an intermediate n-complex to give an intramolecular Co-C(R)=C(R)-N bridge if’no other nucleophile is present. Different reactivity is observed for Co(Por)CI (Por = OEP or TPP) which reacts with alkynes (HC=CR. R = H, COzMe or CHlOH) to give the /3-chloro-vinyl product containing the alkyne inserted into the Co-Cl bond. For example, ethyne itself reacts with Co(TPP)CI to generate Co(TPP)CH=CHCI. In the special case of MeO$ZC=CC02Me, the product of its reaction with Co(OEP)CI is an unusual Co(lI1) porphyrin complex where the intramolecular etheno bridge is between cobalt and a Inrso-carbon atom of’the macrocycle.“” Silyl enol ethers react with Co(Por)X (Por = OEP or TPP. X = halide) to yield stable c~-alkyl cobalt porphyrins. For example. HIC=C(R)OSiMe3 reacted with Co(TPP)CI with net loss of Me$iCl to give Co(TPP)CH$Z(O)R (R == Ph, OEl or vinyl). The reactions were lhster in CHLCI, than in MeOH, and faster lor the weaker Co-X bonds (F > Cl > Br) reflecting the role of’ the SiMe3 group in abstracting the halide. The butadiene derivative CH2=CHCH=CHOSiMej reacted with Co(Por)CI to give only the primary alkyl product, Co(Por)CH$ZH==CHCHO. which could be identified by spectroscopy but was too labile to isolate.“’

VII RHODlUMANDlRlDlUM

A. Overview Structural types for organometallic rhodium and iridium porphyrins mostly comprise five- or six-coordinate complexes (Por)M(R) or (Por)M(R)(L), where R is a a-bonded alkyl, aryl. or other organic fragment, and L is a neutral donor. Most examples contain rhodium. and the chemistry of the corresponding iridium porphyrins is much more scarce. The classical methods of preparation of these complexes involves either reaction of Rh(Il1) halides Rh(Por)X with organolithium or Grignard reagents, or reaction of’ Rh(1) anions [Rh(Por)]- with alkyl or aryl halides. In this sense the chemistry parallels that of iron and cobalt porphyrins.

PENELOPE J. BROTHERS

294 However,

the significant

the Rh(II)

dimer,

It undergoes Rh(Por),

key difference

[Rh(Por)]z,

homolytic

which

dissociation

Rh(Por)H

of’the

dimcr,

(Eq. (16)), driven

dimer of’the

low Rh-Rh

in equilibrium complex

Rh(Por).

with

the monomer. with the hy-

can exhibit

monomer

formed

of’

bond strength.

can also exist in equilibrium

and thus the hydride

by f’ormation

arises from the chemistry

a relatively

and exists

(Eq. ( IS)). The rhodium

dride

for rhodium

exhibits

the chemistry as in Eqs. ( IS)

and ( 16). [ Rh(Por)]?

2Rh(Por)H The

rhodium(I1)

can initiate rr-bonded port

monomer with

organometallic

01‘ CO

chemistry.

the hydride

shown

mechanism,

the chain

with

and (16).

bond

further

developed

useful

by Halpcrn carryin

The key to this rcaction

RI-H

strengths,

and refined

dimer.

instead

odd-electron

report

bond in gcner-

as the insertion

in classical

apparently

lacked

insertion

reactions.

01‘

organomctallic the cis coordiThe reaction

clt a/. in 1985”” to procccd by ;I radical chain g Rh(OEP) fragment formed as in Eqs. (15) is the balance

betwcen

Dada. Another porphyrin

the Rh-Rh.

years Wayland’s

TMP.

and thus nlononleric

Rh-C

research

xncl

group

has

of this type. and assembled

iniportant which

Kh(TMP)

of’ relyin g LII)O~ the equilibriun1

rhodium(

and

to give

the Rh-H This

chemists

the scope of‘reuctions

has been the LW of’ the bulky directly,

Rh(OEP)H for migratory

and in the intervening

array of’thern~ochcmical

of’ the rhodium

organometullic

species

substrates

of this type was the I-Cinto

Rh(OEP)CHO.“”

had not been observed

to be essential

was subsequently

complex

among

bond

(16)

OF organic reaction

the f’ormyl

Furthermore.

variety

The seminal

excitement

site believed

+ Hz

c/ rrl. of’ the insertion

CO into a metal-hydride nation

(IS)

Rh( Por) is an odd-electron

;I wide

products.

to produce

2Rh(Por),

[ Rh(Por)&

reactions

in 198 1 by Wayland

ated considerahlc

+

porphyrin

radical

Rh(OEP)H

+

development does

;I

in thi$ field

no1 allow

formation

can be prcparcd

and LNXI

in Eq. ( IS) as the sourcc

of’ the

II) monomer.

A key step proposed

in the radical

chain

mechanism

for the I‘ormation

01‘ the

lorniyl complex is the coordination of’ CO to the Rh(OEP). monomer. to give an intcrn~cdiate carbonyl coniplex. Rh(OEP)(CO). which then abstracts hydride front Rh(OEP)H

lo give the formyl

product.“g

This

nlcchanisln

was proposed

w,ithout

direct evidence for the CO complex, and since then, again from the research group of Wnyland, various Rh(I1) porphyrin CO complexes, Rh(Por)(CO),. have been observed bridging While

spectroscopically

along

with

further

carbonyl and diketonate complexes. ~netalloporphyrin carbenc complexes

and osmium. they are less well known carbene intermediates were implicated

reaction

products

are well established

which

include

Ihr ruthenium

for rhodium. Cationic rhodium porphyrin et al. in which in a report by Callot

295

Transition Metal Porphyrin Complexes rhodium(II1) transfer

porphyrins

catalyzed

of the ethoxycarbonyl

clopropane

products.‘“”

observed

The

in reactions

by its potential There

in organic

articles.7.x

recent

The only

[Rh(OEP)]z

similar

to rhodium

porphyrin

in three review have

dimers

For example,

Although

and Ir(Por)H

there

parallel

alkyl

of

The

reaction

of Rh(lll) alkyl This

halides

the

halide parallels

RCHzX.

for this

by radical

has lagged

porphyrin

be-

Selected

complexes

in Fig. 7.‘jJ

arc col-

“’

[Rh(Por)(MeNHZ)2]’

reaction dimerize

or attack

elimination

However,

to form

in a-alkyl

was one-electron

and Fe(I1) porphyrins

reactions.

and

of [Ir(Por)lz

quite closely.‘3’~‘33

the latter step involving ofCo(ll)

rhodium

cs-alkyl

are summarized

has been utilired

This can either

the reactions

benzyl

to give

chemistry

complex

halides

proposed

Rh(Por)..

also occur

are shown

rhodium

complexes.

and reactions

congeners

Rh(lll) alkyl

to give methods

surprises

and iridium

cationic with

synthetic

ofthe

n-bonded

and alkynes porphyrin

few

examples

scheme

to form

which

been

rhodium

by reaction

Rh(Por)X

involve

reactions

bromide

recent

of the

syntheses

benzyl

of iridium

have

VI, and several

followed

X~.‘37.‘3x

for iridium.

have been

of rhodium

those of the rhodium

Electroreduction

atom ofthe

to occur

01

reaction

characterization

variety alkenes

More

data for u-bonded

products.

with

the development

in Table

duction

by

reactivity

and (Por)M(R)(L)

with RX. In addition.

reacts

respectively.

(Por)M(R)

5 ‘.’ The classical

monosubstituted

that of rhodium,

CH$YI,

show

the seminal

has not been observed

led to a wide

[Rh(OEP)]l and with

products,

lected

review

is that the insertion

perhaps

and electrochemical

articles:

and iridium

structural

porphyrins

and ketones

porphyrins

species,

complexes

and [Rh(Por)]-

o-vinyl

iridium

spurred

rt ~1.“’

in previous

of aldehydes

;I key difference

chemistry,

with RLi or RMgBr,

con~plcxcs.

of iridium

arc covered

activation

although

and spectroscopic

and iridium

summarized

in the chemistry

cy-

usually

and Iridium (T -Bonded Alkyl and Aryl Complexes

syntheses

rhodium

by Kodadek

to give the formyl

porphyrin

6. Rhodium

hind

of this reaction,

concerns

than

was undertaken

In gcncral.

porphyrins, bond

in organometallic

below.

Further

development

and

to produce

was higher

and electrochemistry

report

diazoacetate

alkenes

of .v~~:cc/zt; products

synthesis,

and [Ir(OEP)]2.

CO into the RhpH

of ethyl

to substituted

have been very few developments Synthesis

The

ratio

of this type.

utility

over the last decade. both

the decomposition fragment

re-

the carbon

of either M(Por)

the results

X. OI with

of a recent

electrochemical study in DMSO su ggest that the Rh(Il) porphyrin is ;I special cast because in the polar solvents required for electrochemistry, the Rh(Por). monoma disproportionates to Rh(lII) and Rh(I) species. and the resulting [Rh(Por)] anion then attacks the alkyl halide in a classical SN2 reaction to give Rh(Por)R and X ~.“‘).2J0A

similarprocess

ctrochcmical

reduction

is implicated of Rh(lII)

in the Formation

porphyrins

ofRh(Por)H

in the presence

from theele-

of Br@nsted

acids.‘“’

Transition Metal Porphyrin Complexes

297

(a)

Cd)

FI(~. 7. M<>lecular \tl-uctwcs plexe\: (a) Rh(OEP)CH1.‘3’.‘X”

ol’ selected organomct;dlic rhodium and il-idium porphyrin con(b) Rl~(OEP)ln(OEP),‘X3 (c) Rh(OEP)C(0)NH(2.6-(_hHtMe2).?“3 (d) Ir(OEP)(CIHx)(PPh3).??‘IRh(TPP)(=C(NHR)~)(CNR)l’ (cr (R=CHI Ph).““(f) Rh(OEP)SiEt3.‘“”

Radiolytic reduction has been investigated as a means of producing transient Rh(I1) porphyrin products. and as in the above study, the observed products were strongly dependent on pH and solvent. Radiolytic reduction of Rh(TMP)CI in alcohol formed transient Rh(TMP). which was prevented from dimerization by the bulky TMP ligand. In alkaline 2-propanol the product is [Rh(TMP)l-, in weakly acidic 2-propanol the hydride Rh(TMP)H is formed, and in strongly acidic 2-propanol the alkylated rhodium(II1) porphyrins Rh(TMP)CHj and Rh(TMP) (C(CH3)zOH) are observed. The alkyl products result from reaction of Rh(TMP). with CHI. and C(CHj)?OH formed by radiolysis of the 2-propanol solvent.‘47

298

PENELOPE J. BROTHERS

The

electrochemistry

where

been studied rhodium

(n =

in detail,

tion or reduction singly

of a series

R = C,,Hl,,+,

reduced

species

donor

ligand.‘J1

can then undergo

Radiolytic

while

of metal hydrides metal

and thermodynamic

effects

the rhodium

porphyrin

mochemical

aspects

OT 25-30

‘. M-H

addition

unfavorable.

with

[Rh(OEP)J,

reactions

paper mediated

the

formed

or, in some cases where bond

intact.“j

A similar

containing

;I neutral

also leads to initial

multiple of many

reduc-

particularly

M-C

bond energies bonds

respectively. which

by Rh(OEP).

2Rh-H

G==

Rh-Kh

Rh-Rh

e

ZRh-

Rh(L)

Rh+L

G=-

EITHER

Rh(L).

+ Rh-H

OR

Rh(L)

+ Rh-Rh

proposed

are usually

(Scheme

arc typically

25-30

to CO or simple

to form reaction were

proceed

(L = CO, CHz=CHPh)

e

Rh-L-Rh

SC‘HtMt.

t 7.

is thcrRh(OEP)of styrcne

rationalized

-1. Hq

RhLH

stronger,

by radical

l7).“”

z

and

in the range

hydrocarbons

(CH?=CHPh)

they

kinetic

the ther715 energics.

kcal rnol-’

and the related that

Both

of these reactions.

in terms of bond

bond energies

with CO or styrene

is a fundamental

in understanding

to give (OEP)Rh-CH&‘H(Ph)-Rh(OEP). in 1985

bonds

substrates.

in the success

has been important

of M-CH

ofRh(OEP)H

or C-O

reactions

are important

or Rh(OEP)CH-CHIPh,

a landmark

oxida-

than either

the initially

of Rh(TPP)R(L)

to C-C

catalyzed

elements.

modynamically The reaction

cleavage the Rh-C

of Rh(TMP)CHl

of these proccsses,

and as a result,

CHO

ring rather

of reduction,

6). has

reversible

Porphyrin Dimer and Rhodium(lll)

chemistry

for first-row

kcal mol

Rh(TPP)R,

ring.2JZ

step in the transition

For example,

Rh-C

retaining

reduction

C. Reactions of the Rhodium(ll) Porphyrin Hydride The addition

In the case

the electrochemistry

tion at the porphyrin

porphyrins,

to be at the porphyrin

ligand.

loss of halide

has investigated

rhodium

(X = Cl. Br, I; II = 3 -

and in each case the site of the initial.

or the alkyl

study

of n-alkyl

6) or (CH2),,X

was concluded

center

R = (CHz),,X,

I -

+ Rh

+ Rh- (L = CHz=CHPh)

in chain

299

Transition Metal Porphyrin Complexes

The key to understanding these reactions is appreciating the relative Rh-Rh. Rh-C. Rh-H, and Rh-0 bond energies, and these have been developed by a series of studies from Wayland’s research group.“’ Overall, the driving force for the radical chain process is the relatively weak Rh-Rh bond and the unusually strong Rh-C bond. This is nicely illustrated by looking at the formation of the formyl complex. For the overall reaction shown in Eq. ( 17). the enthalpy change AH is related to the sulns of the bond energies broken and formed (Eq. 18). Inserting the values for (C=O) - (C=O) = 70 kcal mopi and (C-H) = 97 kcal mom ’ (for an aldehyde) gives the overall expression shown in Eq. ( 19). In other words, the enthalpy change for Eq. ( 17) will be negative when the M-H bond energy is less than 17 kcal mom’ larger than the M-C bond energy. Given that M-H bond energies are Z-30 kcal mom-’ stronger than M-C bond energies. it is easy to see why formyl formation is visually thermodynamically unfavorable. Including an estimate for the entropy term (at 25% K) results in an even more stringent condition, in which AG will bc negative only when the M-H bond energy exceeds the M-C bond energy by no more than 9 kcal mol ‘.2”5 M-H

AH

= (M-H) AH

+ CO + M-CHO

+ ((30)

= (M-H)

- (M-C) - (M-C)

(17)

- (C=O) - (C-H)

- I7

heal

mol

’

(IX) (I’))

In the specific example involving the rhodium porphyrin hydride and formyl complexes. Rh(OEP)H and Rh(OEP)CHO. the Rh-H and Rh-C bond energies (62 and 58 kcal mol-‘. respectively) have been determined by equilibrium mcasurements. This is an unusual example where the Rh-H bond energy is in normal range but the Rh-C bond energy is unusually large. As a result the reaction to form the formyl complex is thermodynamically favorable and the difference in Rh-H and Rh-C bond energies is less than 9 kcal mol-‘. Addition of Rh(OEP)H to formaldehyde, ethene. and ethyne are also thermodynalnically favorable. The Rh-Rh bond dissociation energy in [Rh(OEP)], (16.5 kcal mol -‘) has been estimated from kinetic studies based on ‘H NMR line broadening. The Rh-Rh bond dissociation energy is relatively weak, permitting facile bond homolysis to generate the Rh(OEP). radical. This also has a favorable thermodynamic effect on the addition reactions of [Rh(OEP)], with CO and alkenes.‘J’ Electronic effects on the reactions of [Rh(Por)]l dimers and hydrides were probed by varying the porphyrin macrocycle. OEP and TPP vary considerably in their properties, with OEP being one of the strongest and TPP one of the weakest n-donors among porphyrin derivatives. However. [ Rh(Por)]?, Rh(Por)H, and [Rh(Por)]- showed the same reactivity in a variety of reactions for both OEP and TPP, indicating that electronic effects relating to the porphyrin ligand have

300

PENELOPE J. BROTHERS

little influence.“” A more dramatic electronic effect was achieved by using the octaethyltetraazaporphyrin macrocycle OETAP (in which the III~JSOCH groups of OEP have been replaced by nitrogen atoms). which is both a strongero-donor and ;L strongern-acceptor than OEP. A comparison ofthe reactions of[Rh(OETAP)], and IRh(OEP)]2 showed that both reacted with cthene, CHJ, CNMe, and P(OMej),j, but only (Rh(OEP)j? reacted with Hz. HZ/CO. CHICHO. and CH3ChH5. Equilibrium studies indicated that the Rh-Rh dissociation enthalpy of [ Rh(OETAP)Il is larger than that of [Rh(OEP)]?, although it is not easy to rationalize this with the different electronic properties of the two macrocycles,’ Both the [ Rh(OEP)]J and [Ir(OEP)]z dimers reacted with thea-CH bonds in aldchydes and ketones. This is unusual because the stronger alkyl C-H bond reacted in preference to the weaker aldehydic C-H bond. For example. 2-methylpropanal reacts with [ Rh(OEP)]? to give the P-formyl complex as the kinetic product. although this rearranged to the acyl complex which is the thermodynamic product (Ey. (20)). An explanation for this is that the dimers react initially with the enol tautomcrs of the aldehydes or ketones to give a bridged intermediate. M-CR?-CR(OH)-M (analogous to the reaction of the dimers with alkcnes) which then dissociates (Gvc the P-carbonyl dcrivativc with hydrogen migration from the OH group to ,= M-CR,C(O)R together with M(OEP)H.‘JX [Rh(OEP)j2 + Me?CHCHO + (OEP)Rh-CMe,CHO + (OEP)Rh-C(0)CHMel

(20)

Diol dehydratase is an enzyme which functions together with coenzyme Blz to catalyze the dehydration of vicinal dials to aldehydcs. A cobalt- 13dihydroxyalkyl intermediate has been proposed to occur in this process, but has never been directly observed in either the cobalamin or model cobalt porphyrin systems. A consequence of the strong Rh-C bond is that cu-hydroxyalkyl complexes have been observed to form from the reaction of Rh(Por)H with aldehydes (Eq. 21). This reaction has been studied using glycoaldehyde as a model for diol dehydratase, producing Rh(OEP)CH(OH)CH70H (characterized by ‘H NMR) which slowly dehydrates to form Rh(OEP)CH$HO.“” Rh(Por)H + RCHO + Rh(Por)CH(OH)R

(21)

The radical Rh(Por). generated from homolytic dissociation of [ Rh(Por)]z rcacts with alkenes CH,=CHX to produce an intermediate metaltoorganic radical (Por)RhCH$HX.. which then reacts with [Rh(Por)ll to produce the dinuclear complexes (Por)Rh-CH&H(X)-Rh(Por) (Eqs. 22-24). If the intermediate metalloorganic radical (Por)RhCHzCHX. is intercepted by the alkene rather than by the rhodium dimer. then the result could be alkene dimers, oligomers, or polymers. This possibility was investigated for acrylate substrates, CH?=CH(CO?X) (X = H, CH3, CHICHI). With IRh(OEP)j2, the two-carbon bridged product

Transition Metal Porphyrin Complexes

301

tHX I (23) w

+ H,C=CHX

G====-=

(OEP)RhCH$H(CO2X)Rh(OEP) is formed. Two stereoisomers were observed, resulting from inhibition of rotation about the CH-COlX bond. The bulkier conplex Rh(TMP). inhibits formation of the two-carbon bridged product, and a fourcarbon bridged compound, (TMP)RhCH$H(CO~X)CH(CO~X)CH~Rh(TMP), results from head-to-head dimerization ofacrylate and contains two chiral centres. The Rh(I1) monomers Rh(Por). do not initiate thermal polymerization ofacrylates. However. Rh(TMP). does catalyze a photopromoted polymerization of acrylates that has living character, with NMR evidence observed for one Rh(TMP) unit attached to an oligomer of up to 15 methyl acrylate units.“” Alkyl radicals R. can initiate alkene polymerization to form a new radical RCH$ZH, since formation of a strong C--C bond (85 kcal mol ‘) more than compensates for loss of the alkene n-bond. However, even though (Por)Rh-C bonds are unusually strong, (Rh-CHI z 58, Rh-CHZR 5 50, Rh-CHR? (40 kcal mol-‘). reaction of Rh(Por). with ethene to form (Por)RhCH2CHz. will still be thermodynamically unfavorable. The initial product of the reaction of Rh(Por). with the alkene. [(Por)Rh(CH2=CHX)1’. was described as a metalloradical-alkene complex, which either underwent attack by a second Rh(Por) unit or dimerised, forming the two- or four-carbon bridged product, respectively. (Por)RhCH$H,. does not behave as a true carbon-centerd radical, and although (OEP)RhCH,CHX. can form from Rh-C bond homolysis of the two-carbon bridged product, it cannot initiate alkene polymerization. However, photochemically induced Rh-C bond homolysis of the four-carbon bridged product (formed from Rh(TMP). with CH?=CHX) produces (TMP)RhCH$ZH(C02X)CH(C02X)CHZ. which does have carbon-centered radical character, and can thus initiate the polymerization process. as observed experimentally.250 Using the very bulky rhodium porphyrins Rh(TTEPP). and Rh(TTiPP). (which contain triethylphenyl and triisopropylphenyl groups), neither of which can dimerire. direct evidence for an alkene adduct and its subsequent dimerization to the fourcarbon bridged product has been obtained. Reaction of Rh(TTEPP). with ethene

302

PENELOPE J. BROTHERS

in benzene ethene

gives quantitative

adduct

(S =

l/L))

bridged

and slowly

product.

C-H

proximately

activation

:tmounts

and isopropyl

benzene

ucts bearing

the Rh(OEP)

the alkyl

products

substituted

is further

[Rh(OEP)?]. and

species, bonds

in alkyl

C-H

action

:ttom.

The

[Rh(OEP)lj

itnportance

Unactivated homolysis quirements strength. might

Ltlkancs

times

to a lesh

at the benzylic

fitils to react

Rh(OEP).

’ weaker

C-H

than aryl or unactivated

stron, (T Rh-C bond makes the realcohols PhCH(OH)R also react

Benzyl to give which

with

as the attacking

Rh(OEP)H

and an intcrtnediate

lhcn eliminates

RC(O)Ph

and pro-

of‘ Rh(OEP)H.“” did not react because

but do not weaken

be feasible.

Rhodium

(tetraxylylporphyrin)

with

this aim. The

I2 kcal mol -‘) plex. Rh(TMP). reversibly

Rh(Por)CHj

dimer

the Rh-C complexes and T M P

of the energy

with

and Rh(Por)H

(Fig. 8). This synchronizes mation ot’ the new Rh-C

an essential

bond.

coat 01‘ Rh-Rh

activation

of stronger

of two sterically

encumbered

(tetramesitylporphyrin).

[ Rh(TXP)I?

has a smaller

than the OEP congencr. while . that does not dinicrize.‘5’.‘5i methane

at modest

its products.

together with equilibrium constant anistn involvingatritnolccular.4centered,

new bonds

procl-

on the basis that benzylic

kcal mol

C-H

kinetic at longer

bonded

reaction

ap-

benzene

bond

in the dimer [Rh(OEP)Jz (ca. I6 kcal mop’). By introducing stcric reon the periphery of the porphyrin ligand that reduce the Rh-Rh bond

TXP

reacted

to give

rhodium

to involve

of the relatively

at the benzylic

Ethyl

although

with

is explained

favorable.“’

molecule

position

of Ihe initial

is proposed

to produce

Rh(OEP)H.

at the a-position,

(OEP)Rh-CR(OH)Ph

duces ;I further

hotno-

was first rc-

toluene

by the fact that t-butylbenzenc

Formation

thermodynamically

with

and

to the compounds

the regioselectivity

a-hydroxyalkyl.

require

by [ Rh(OEP)z]

reacts

react at the benzylic

substituent

mechanistn

bonds.

four-carbon

as this would

aromatics

[Rh(OEP),]

(8.5 kcal m o m ‘) ;trc cit. IS-20

alkyl with

both

illustrated

The

the analogous

solution

bond?

of’ Rh(OEP)CH,Ph

rearrange

cat-bon

position

Rh-CH,

For cxatnple,

equal

to give

are not observed.

The

by EPR in frozen

by Rhodium Porphyrins

bond

in l98S.‘5’

in solution

oligotncrs

strong

Activation

BenLylic ported

of (TTEPP)Rh-(CH2)4-Rh(TTEPP). can be observed

ditnerizes

Higher

ysis of the relatively

D. C-H

formation

Rh(TTiPP)(CHz=CHz).

breaking (57 kcal

TMP

were

Rh-Rh

bond

I‘orms ;I stable

C-H

bonds

porphyrins, investigated strength Rh(l1)

(ca. con-

Both IRh(TXP)I, and Rh(TMP). temperatures and pressure\ to give

Observation

of a large kinetic

measuretnenla were IincLtrtl-ansition

consistent state Rh.

isotope with .C.

effect

a mcch.H. .Rh

of the C-H bond (I05 kcal molmm’) with lot-molt’) and Rh-H (60 kcal mol -‘) bonds.

feature when the bond being broken is stronger than each of the being formed. Aromatic C-H bonds do not react with [Rh(TXP)]z ot

Transition Metal Porphyrin Complexes

303

Rh(TMP). under these conditions, and in fact the selective activation of methane in benzene solution is a distinctive and unusual feature of this system, given that aryl C-H activation ought to be thermodynamically favored over alkyl C-H activation. The proposed linear transition state proposed in Fig. 8 is the key to this different reactivity. The corresponding trimolecular transition state for an arene would be expected to be bent, and this would be precluded by the bulky TMP ligands.‘5’.‘5J The activation of the benzylic C-H bond in toluene is believed to occur through ;I similar transition state. as is the reaction of Rh(TMP). with Hz to produce Rh(TMP)H.‘55 The proposed mechanism was further tested by the synthesis of a new, dinucleal porphyrin containing two mrso-trimesitylporphyrin groups. each linked through the fourth porphyrin IIWSO position by a C~,HJO(CH~)~,OC~,HJgroup. This new porphyrin behaves essentially as two, covalently linked TMP units, and forms a diradical containing two Rh” centers, abbreviated as Rh(PorO(CH,)hOPor)Rh. that is prccludcd from dimerization. Linking ofthe two porphyrins improves the entropy term required to achieve the linear, 4-centered transition state. Activation of CHd proceeds with only intramolecular formation of CH3Rh(PorO(CH?)(,OPor)RhH, and with faster kinetics than either [Rh(TXP)]? or Rh(TMP)-.“” In classical mechanisms for C-H bond activation either C-H a-bond donation or cyclic, J-centered transition states are important, but these are precluded in the porphyrin systems and the mechanism proposed for activation of CH.$, toluene. and Hz by the Rh” porphyrin radicals is a new mechanistic possibility.

E. Activation

of CO and lsocyanide

by Rhodium

Porphyrins

One step of the mechanism determined for the reaction of Rh(OEP)H with CO to give the formyl complex Rh(OEP)CHO involved the coordination of CO to the chain-carrying Rh(II) porphyrin Rh(OEP)., although there had been no direct evidence observed for this species. “‘) Since that time, Wayland has systematically developed the chemistry of Rh(Il) porphyrins coordinated to CO, and the chemistry is now well understood. The investigation began with the observation that two species could be observed by NMR and IR spectroscopy in solutions of [ Rh(OEP)]z in toluene-cl8 exposed to CO. The first. which forms immediately, has 11~0= 2094 cm-’ and a broad peak

304

PENELOPE

at 1X0 ppm

in the ‘“C NMR

[Rh(OEP)],(CO). I733 cn1-l

kcal

pressures

product.

an AA’XX’

double

depends

driving

force

5 kcal mop’

steric

arrangement. unfavorable

product)

the increased

arrangement. distance

introduced

The

with

is likely

to have a 20&30 hypothesis

S =

and “CO

observed

I /2 and coupling coupling

ligand.

dimerization

suggest about

ol

product

from

product

carbon

Lu-diketone

I : I adduct. constant

unit.

to the dimetal Rh(TTiPP)CO.,

occurs.

Equilibrium

more

a-diketone.

demanding

with

solution

with CO permitted

the

by EPR spectroscopy,

““Rh

and “CO.

The g value is delocalized

the loss of axial

symmetry

in solution. the Rh(TMP)CO, In the even more sterically deCO adduct

is stable

and dissociation

linked

Ii-

a-diketone

for the CO adduct

of dimerization

but

porphyrin

the dimetal

have allowed

The two covalently

degree

favorable

on Ru(TMP)CO

ment of the enthalpies

a

insertion

unit is not planar

that the odd electron

a-diketone.‘5”.‘“’ the paramagnetic

dimetal

cr-diketone.‘5”

a

ot in

bond.‘“”

At low temperature

studies

(the double

allow

Rh(TMP)CO,,

toluenc

results

for the dimetal

sterically

indicate

proximity

atom

rings and the added bond

observed

of the odd electron

increase

more favorable

a

the close

ketone

the C-C

The thermodynamic

is the estimated

that the diketone

usin g a more

and in frozen

a bent Rh-CO

species dimerizes manding complex

proportion

with

of a paramagnetic

the CO

I’(‘() values

rotation

and the relative

CO (I atm, _98 K) to give The reaction of Rh(TMP), product.‘“”

reacts

hypertine

suggested

two

simulation,

was tested

[Rh(TXP)]?

observation

onto

structure

and

bond, arising

the C-C

at

and single

the porphyrin

around

for the diketone

CO adduct.

and pressure.

insertion

between

and

CO insertion consistent

are observed

In the dimetal

by rotation

arrangenient.“x

as the only

CO

temperatures

as the double

(the dimer,

Rh-C

’) and an entropy

lower

shift ofthe

insertion

ofthe

(ca. 50 mom ’).

multiplet

a

in equilibrium,

double

bonds

( I6 kcal

chemical

and the .s$ hybridized

together This

ofthe

and

four-line

as

temperature,

In the single rings

sterically of freedom

exist

in the strength

the two porphyrin

Rh-C

bond

using

IJC‘() stretches

on the porphyrin,

spectrum,

The ‘jC NMR and appears

Two

products)

strong

was identified

All four compounds

for formation

ofca.

with

species

adduct,

has t’(~() =

In thermodynamic

of the Rh-Rh

investigation.

at 165.5 ppm.

spin system.

slowly.

from three to two (72 kcal mol

of CO, a third

CO insertion

products

gand.

of sufficiently

On further

1782 and 1770 cm-‘.“”

steric

formation

bond order

occurs

more

= 44 Hz) in the ‘?C NMR

(OEP)Rh-C(0)-C(O)-Rh(OEP).LiX

new product

to be ;I simple

evolved

(OEP)Rh-C(O)-Rh(OEP).

for cleavage

(7.5 kcal moF’).‘57

higher

with

requires

of the C-O

which

at I I6 ppm (‘.JR~-(,

’) to compensate

reduction term

and was proposed

species,

to a dimetallaketone,

this reaction mol

spectrum.

second

and a triplet

was assigned terms,

The

J. BROTHERS

rhodium(l1)

porphyrins

in the C-H activation studies described above), .Rh(PorO(CH2)bOPor)Rh.. with CO to produce the tethered diradical .(OC)Rh(PorO(CH,)(,OPor)Rh(CO). which intramolecular coupling to form the diketone was also observed.“’

and no

measurcfor the (as used react for

Transition Metal Porphyrin Complexes

305

In the TMP system the monomer Rh(TMP)CO and dimer (TMP)RhC(O)C(O)Rh(TMP) are in equilibrium. When this mixture is treated with styrene and repressurized with CO the styrene insertion product (TMP)RhC(O)CH2CHtPh)C(O)Rh(TMP) is observed by ‘H and ‘jC NMR. As expected, this compound has two chemically different CO groups.“” When CO is added to a mixture of Rh(TMP), and Rh(TMP)H, the products consist of a mixture of the hydride, the monomeric carbonyl adduct, and the cu-diketone dimer. but no formyl complex is observed. This is interesting because hydride abstraction from Rh(OEP)H by the carbonyl complex Rh(OEP)CO. is proposed as a step in formation of the lormyl product in the OEP system (Scheme 17). The increased steric bulk of the TMP ligand in Rh(TMP)H must preclude this step, but Rh(TMP)CO. will react with less steritally demanding hydride sources (HSnBui or Hz) to produce the formyl complex Rh(TMP)CHO.“” The tethered diradical .(OC)Rh(PorO(CH2)~0Por)Rh(CO). reacts with water, ethanol and Hz to form HRh(PorO(CH7)(,0Por)RhCH0, H(O)CRh (PorO(CH7)(,0Por)RhC(0)OEt, and H(0)CRh(PorO(CH2)(,0Por)RhCH0, respectively.‘“’ Overall, the chemical reactivity of Rh(TMP)CO. is likened to that of the acyl radical, CH&O.. and represents an unusual example of a 17-electron metal carbonyl complex which exhibits carbon-centered rather than metal-centered radical reactivity.“’ The formal relationship between CO and isocyanide ligands. CNR, apurkcd a comparative study of the reactions of CNR with Rh(OEP)H, [Rh(OEP)]z and Rh(TMP).‘“j As with CO, the initial reaction of [Rh(OEP)]z with CNR (R = Me, Et) leads to a 2: 1 adduct, [Rh(OEP)]$CNR). although the equilibrium constant fat formation of the CNR adduct (- IO’ at 29X K) is much larger than that corrcsponding to formation of the CO adduct (-4X at 29X K). Subsequent chemistry is different as the CNR adduct slowly transforms in solution to a mixture of Rh(OEP)R and Rh(OEP)(CN)(CNR), driven by CN-R bond cleavage. No evidence is seen for a bridging imine or diimine. When an aryl isocyanide is used. CN-R bond cleavage does not occur and reversible formation of the adduct occurs cleanly. The reaction of Rh(TMP). with CNR (R = Me, rl-Bu) gave the I: I adduct, Rh(TMP)(CNR). although CN-R bond cleavage is also a problem. No evidence was seen for a bridging iminc or diimine complexes, probably a result of the increased steric requirements of an isocyanide relative to CO.‘“3 Rh(OEP)H reacts with CNR (R = MC, rr-Bu.) to give the adduct Rh(OEP)(H)CNR (which has no parallel in CO chemistry) which then slowly transforms to the formimidoyl insertion product, Rh(OEP)C(H)=NR. The dimer [ Rh(OEP)]? reacts with CNAr (Ar = 2,6-Cc,H3Me2) in aqueous benzene to give the carbamoyl product. Rh(OEP)C(O)NHAr (characterized by an X-ray crystal structure) together with the hydride, which itself reacts further with the isocyanide. This is suggested to form via a cationic carbene intermediate. formed by attack of HZ9 on coordinated CNAr in concert with disproportionation to Rh(lll) and Rh(l).‘“’

306

PENELOPE J. BROTHERS

F. Reactions Aryl

of Rh(lll) and Rh(l) Porphyrins

C-H

activation

in the reaction Anisole,

by cationic

of Rh(OEP)CI

toluene, phenyl

derivatives.

mechanism

ofthis

process

electrophile

is the [Rh(OEP)]+

cate that the [Rh(OEP)]’

When

the highly

responding

substituted

by coordination

at the a-CH [ Rh(OEP)]j enol

the enol oxygen aldol

cnol with

of Rh(OEP)CI

bonded

condensation. center ketones

appended enolization.

but rather

the aldol

rather

bonded

reactions

provide

containin wa\

porphyrin carbon

bonded

an example

base (pyridyl

com-

reacted

acidic direct11

or aryl alcohol) base assists

ring-opening

reactions

products

than the carbonyl

toward

the Lewis

intramolecular

induced

The

is believed

/-carbony

where

g a mild The

with

formed.

does not show any activity

to give organomctallic rather

that the

reaction

product

Rh(OEP)CI

used.

ketones

reacts with

an olpanorhoclium

formation.‘“’

[Rh(OEP)]

ring lactoncs

to the alkoxide

linked

the vacant

indicates

’ . and the intermediate

than the Rh--C

wl~en a porphyrin

to the IIKJSO position 26X Rh(l)

acetone

and an initial

condensation

prepared.

enolate

The anionic

with

reacts with

The regiochemistry

by [Rh(OEP)]

enolatc

These

Ag+)

For example,

arc involved.

is used to promote

4- and S-membered

polymer.

group

with

products.

The latter. when indepcndcntly

Rh(II1)

was used, the cor-

In the case of cyclohexanone,

is catalyzed

to be the Rh-0

with RhCl.;.xH?O

and Rh(Por)(,n-C,HICN).l”

of OIW Rh-CnH&N

than the ketones

was proposed.

condensation

pound.

nitrogen

aryls indi-

to electrophilic

as a coordination

crystallized

by reaction

was not observed,

product

(60%)

that the where the

to that of NOZ1.‘“’

of HJPor (Por = OEP, TTP)

of Rh(Por)CI

to give fi-carbonyl

rather

similar

was also attributed

to give (OEP)RhCH?C(O)CH;.

tautomcrs

substitution,

rhodium.‘“”

(formed position

constant

the /U/Y-

indicatea

tctramesityloctaphenylporphyrin

of the CN

axial site on an adjacent

reaction

on ;I series ofsubstitutcd

activation

product

Rh(OEP)C6H5.

exclusively

aromatic

Studies

gave

giving ofthe

has a Hammet

C-H

mixture

a

organometallic

[Rh(OEP)]+

cation.

The reaction

gave

has also been established which

react similarly,

is allied to elcctrophilic

arenc

substitution.

in benzonitrile

porphyrins in benzene

The regiochemistry

cation

unexpected

aromatic

Ag+

and chlorobenzcne

substituted

Similarly,

Rh(II1)

with

with Organic Substrates

with with

with the rhodium

carbon.‘“”

The chemistry of [Rh(OEP)]l in bcnzcne i\ dominated by Rh-Rh bond homoysis to give the reactive Rh(I1) radical Rh(OEP)-. This contrasts with the reactivity of [Rh(OEP)]? in pyridine. which the thermodynamically favorable with

the Rh(1)

NMR

chemical

anion,

[Rh(OEP)]-

shift changes

promotes Rh(III),

disproportionation via the formation ot rl” complex [Rh(OEP)(py)?]+ togethel

.27” The

in pyridine

hydride

consistent

forming Rh(OEP)H(py). Overall. solutions an equimolar mixture of [Rh(OEP)(py),]+and

complex

Rh(OEP)H

with coordination

of [ Rh(OEP)]l (Rh(OEP)]-.

shows

of pyridinc.

in pyridine behave a5 For example, reaction

307

Transition Metal Porphyrin Complexes

of this solution with Hz produces Rh(OEP)H, an unusual example of heterolytic activation of dihydrogen’77 where H+ and HP react with a metal anion and cation. respectively, to give the same product. Despite the different formulation of the species in solution, the overall reactivity of [Rh(OEP)]z in benzene and pyridine is remarkably similar. with ]Rh(OEP)(py),]+ and [Rh(OEP)]- in pyridine reacting with H?/CO or H,O/CO to give the formyl complex Rh(OEP)(CHO)(py). In this case activation of CO is proposed to occur through the metalloanion [ Rh(OEP)]-.“” G. Rhodium Porphyrin Carbene Complexes and the Cyclopropanation of Alkenes Catalyzed by Rhodium Porphyrins

In 1980 and 1982. Callot and co-workers reported that Rh(Por)I catalyzed the reaction between alkenes and ethyl diazoacetate to give .SJYIcyclopropoanes as the major products (Eq. 2.5).‘“” This was unusual as most transition metal catalysts for this reaction give the anti isomers as the predominant products. Kodadek and coworkers273 followed up this early report and put considerable effort into trying to improve the .sy7/m7ti ratios and enantioselectivity using porphyrins with chit-al substituents.

+

N,CHCO,Et

(25) w

anfi CHCO,Et

Details of the mechanism of the cyclopropanation reaction were elucidated by a careful study of the reactions of Rh(TTP)I and Rh(TTP)CHj (which can also act as a catalyst) with ethyl diazoacetate in the presence and absence of an alkene, to give the overall process shown in Scheme IS.““-“” Species which have been observed directly by spectroscopy are the alkyl diazonium and iodoalkyl complexes ](TTP)Rh-CH(N?)CO,Et]+ (at -40 ‘C) and (TTP)Rh-CH(I)C02Et. The latter species was determined to be the actual catalytic species participating in the cycle, as shown in Scheme I 8.273The cyclopropanation event occurs by transfer of a carbene fragment from a rhodium carbene complex (not directly observed) to the alkene substrate. The stereochemistry of the resulting cyclopropane product (.SJXvs crjrti) was rationalized from a kinetic study which implicated an early transition state with no detectable intermediates. Approach of the alkene substrate perpendicular to the proposed carbene intermediate occurs with the largest alkene substituent opposite the carbene ester group. This is followed by rotation of the alkene as the new C-C bonds begin to form. The steric effect of the alkene substituent determines

308

PENELOPE J. BROTHERS

+

Rh+

Sc~llthlt:

IX

whether clockwise or anticlockwise rotation occurs, depending on whether porphyrin/substituent or ester/substituent interactions predominate. leading to either a .SJHor anti product.“’ Attempts to improve the syrdunti ratio and enantioselectivity were made by appending bulky binaphthyl or ort!zo-pyrenylnaphthyl groups to the nzeso porphyrin sites, creating a “chiral wall” or even bulkier “chiral fortress” porphyrin, respectively. Although in each case relatively good swdmti ratios (in the range 2-8) were obtained for a variety of alkenes, enantiomeric excess values (ee) remained only modest, in the approximate range 1040%, with the mti products generally exhibiting better ee values than the .SJYZ products.‘7’m’77

Transition Metal Porphyrin Complexes

309

Rh(Por)l (Por = OEP. TPP, TMP) also acts as a catalyst for the insertion of carbene fragments into the O-H bonds of alcohols, again using ethyl diazoacetate as the carbene source. A rhodium porphyrin carbene intermediate was proposed in the reaction, which is more effective for primary than secondary or tertiary alcohols, and with the bulky TMP ligand providing the most selectivity.‘7x Both rhodium and osmium porphyrins are active for the cyclopropanation of alkenes. The higher activity of the rhodium porphyrin catalysts can possibly be attributed to a more reactive, cationic carbene intermediate, which so far has defied isolation. The neutral osmium carbene complexes are less active as catalysts but the mono- and bis-carbene complexes can be isolated as a result. Although rhodium porphyrin carbene species are believed to be the key intermediates in the alkene cyclopropanation reactions, few examples of rhodium porphyrin carbenes have been fully characterized. Nucleophilic attack on coordinated isocyanide ligands to give carbene ligands is well known, but not well explored for porphyrin systems. [Rh(Por)(CNR)z]+ (Por = OEP. TPP; R := CHzPh. />-C(,HJ) reacts with methanol (as the nucleophile) although the carbene products are formulated as [(Por)Rh=C(NHR)2]i. Minor products from these reactions arc the methoxycarbonyl and amide complexes (Por)Rh-C(0)OCH3 and (Por)Rh-C(O)NHR, presumed to result from hydrolysis reactions producing the free amine, H1NHR. which then ends up as a substituent on the carbene ligand. An X-ray crystal structure of [(TPP)Rh=C(NHCH,Ph),(CNCH2Ph)]PFc, shows it to contain an isocyanide ligand in the position tn~rs to the carbene (Fig. 7). Both the Rh-C(carbene) and Rh-C(isocyanide) bond lengths, 2.030( I I) and 2.064( 13) A. respectively, are long compared to non-porphyrin rhodium carbene and isocyanide distances. and are presumed to reflect a tr-cry influence. “” In fact, both these distances are not significantly shorter than Rh-C single bonds in a-bonded Rh(Por)R complexes, for example I .970(4) and 2.0 I3(6) for the Rh-C bond lengths in two different determinations of Rh(OEP)CH+lXO The electrochemistry of the carbene complex [(TPP)Rh=C(NHCH2Ph)2(CNCH2Ph)]PFc, has been investigated.‘x’

H. Heterobimetallic

Rhodium

Porphyrin

Complexes

A number of the reactions by which organometallic rhodium porphyrin complexes are prepared have parallel reactions with inorganic substrates. giving rise to “inorganometallic” rhodium porphyrin complexes. ]Rh(OEP)]? reacts with a variety of silanes and stannanes, including Et$iH, PhSiH, n-BuSnH, and PhSnH to give the rhodium silyl and stannyl complexes Rh(OEP)SiR? (R = Et. Ph) and Rh(OEP)SnR3 (R = rz-Bu, Ph) together with elimination of H2.76LlAn alternative synthesis of a rhodium silyl utilizes [Rh(TPP)]- with Me+SiCl, giving Rh(TPP)SiMei.‘*’ Three complexes, Rh(OEP)SiEt;,‘“” Rh(OEP)SiMe~,2X’ and Rh(TPP)SnC13,2X3have been characterized by X-ray crystallography, and exhibit

310

PENELOPE J. BROTHERS

Rh-Si or Rh-Sn bond lengths of 2.32( I ). 3.035(2) and 2.450( 1) A, respectively (Fig. 7). [Rh(OEP)]- reacts with In(OEP)CI in THF to give the heterobimetallic diporphyrin complex (OEP)Rh-In(OEP), which has a Rh-In bond length of2.584(2) A. 3 slightly shorter than the sum of the covalent radii (2.62 A) of rhodium and iridium (Fig. 7). This compound reacts with CHJI to give Rh(OEP)CHj and In(OEP)I, and with acids HX to give Rh(OEP)H and In(OEP)X, but showed no activity toward many of the reagents that react with [ Rh(OEP)]l under similar conditions (H?/CO. slyrene or acrylonitrile). Furthermore. the compound shows no tendency to coordinate donor ligands (CNBu. H?O or P(OEt)l) at the rhodiutn center. On the basis of its chemical reactivity the complex is considered to be a donor-acceptor conplex, with rhodium retaining its Rh(1) anion character with a tilled r/,2 orbital, and indium its In(II1) character.“” A selection of other derivatives (Por)Rh-In(Por) containing different porphyrins have been prepared, as have the thallium analogucs (Por)Rh-Tl(Por) which show similar reactivity.‘x5m’x7

VIII THE LATE TRANSITION

METALS

(GROUPS

10, 11, AND 12)

A. Overview

Organometallic porphyrin complexes containing the late transition elements (from the nickel, copper. or zinc triads) are exceedingly few. In all of the known examples. either the porphyrin has been modifed in some way or the metal is coordinated to fewer than four of the pyrrole nitrogens. For nickel, copper, and zinc the +2 oxidation state predominates, and the simple M”(Por) complexes are stable and resist oxidation or modification. thus on valence grounds alone it is easy to understand why there are few organometallic examples. The exceptions. which exist for nickel, palladium, and possibly zinc, arc outlined below. Little evidence has been reported for stable organometallic porphyrin complexes of the other late transision elements.

B. Nickel

Nickel porphyrin complexes containing a bridging carbene ligand have been known for some 25 years. Ni(TPP){/L-(Ni,N)-CHC02Et) was prepared by the reaction of the nickel(B) N-alkyl porphyrin [Ni(TPP-NCH$ZO?Et)]+ with base, and has been characterized by crystallography (selected data are given in Table V). The nickel is bonded to only three of the pyrrole nitrogens, with a long Ni. .N

Transition Metal Porphyrin Complexes

311

distance (2.610(3) A) to the alkylated pyrrole.“” A related vinylidene porphyrin, Ni(TPP){ kl-(Ni,N)--C=CAr?} (Al- = p-C6H~CI). was prepared by the reaction of the N,N-vinylidene-bridged free-base porphyrin with Ni(CO)+‘“” In each of these complexes, the carbene fragment has alkylated one pyrrole nitrogen, reducing the charge on the porphyrin ligand to - I, and thus the Ni” center can form a bond to the carbene carbon to achieve a neutral complex. This principle has also been demonstrated for an N-alkyl porphyrin. Ni(TPP-NMe)CI (containing the N-methyl TPP ligand) reacted with PhMgBr at -70 C to give a complex assigned by ‘H NMR and EPR spectroscopy to be Ni(TPP-NMe)Ph. The complex is paramagnetic (S= I), in contrast to the diamagnetic bridging carbene nickel complexes. A thiaporphyrin H(SPor), in which one pyrrole NH group ia replaced by a sulfur atom, thus forming a monoanionic N3S donor ligand. behaves similarly. forming Ni(SPor)Ph from Ni(SPor)CI and PhMgBr at -70 C, again detected by spectroscopy. Both Ni(SPor)Ph and Ni(TPP-NMe)Ph decompose upon warming above -70 C.‘“’ A diaoxaporphyrin (O?Por). in which two pyrrole NH groups are replaced by oxygen atoms, is a neutral N?Oz donor ligand. At -70 C. Ni(O~Por)Cl~ reacts with one or two equivalents of PhMgBr to give Ni(02Por)PhCl or Ni(O,Por) Phz.‘“’ Finally. the unusual porphyrin isomer in which one pyrrole ring i\ inverted. with the nitrogen atom on the periphery of the ring and a CH group pointing into the cavity forms both Ni(II) and Ni(ll1) complexes containing an Ni-C bond to the carbon in the inverted pyrrole ring.“”

C. Palladium

Until very recently, metalloporphyrin n-ally1 complexes were unknown, but this has changed with the report of one example containing palladiurn.‘y3 Like the organometallic nickel porphyrins, N-alkylation of the porphyrin is a feature of this new complex. In this case, the free-base porphyrin (TPP-NN) bears an N”. N”-etheno bridge, in which a PhC=CPh group bridges between two adjacent pyrrole nitrogens. The etheno-bridged porphyrin (TPP-NN) coordinates as a neutral Ii&and, forming a complex with B PdCl2 fragment in which the palladium atom lies considerably out of the porphyrin plane and is coordinated only to the two non- alkylated pyrrole nitrogen atoms. Pd(TPP-NN)CI: reacted with AgCIOl followed by the allyltin reagent, CHz=CHCH$nBu3. to give the cationic ~-ally1 complex [Pd(TPP-NN)(q3-C,H5)] ‘. Two isomers were identiiied by ‘H NMR spectroscopy, presumed to differ in the orientation of the ir-ally1 ligand with respect to the palladiuln porphyrin fragment. One isomer was characterized by X-ray crystallography. and showed Pd-C distances (2.085(7) and 2.125(7) A) similar IO those observed in related n-ally1 palladium bipyridine complex. Thus in this case, the porphyrin is behaving essentially as a neutral, bidentate nitrogen donor ligand.‘”

312

PENELOPE J. BROTHERS

D. Zinc

‘H NMR data has been reported for the ethylzinc complex, Zn(TPP-NMe)Et. formed from the reaction of free-base N-methyl porphyrin H(TPP-NMe) with ZnEt,. The ethyl proton chemical shifts are observed upfield, evidence that the ethyl group is coordinated to zinc near the center of the porphyrin. The complex is stable under Nz in the dark, but decomposed by a radical mechanism in visible light.‘“J The complex reacted with hindered phenols (HOAr) when irradiated with visible light to give ethane and the aryloxo complexes Zn(TPP-NMe)OAr. The reaction of Zn(TPP-NMe)Et, a secondary amine (HNEt?) and CO, gave zinc carbamate complexes, for example Zn(TPP-NMc)OlCNEtz.‘C)5

IX

NON-COVALENT

INTERACTIONS BETWEEN METALLOPORPHYRINS AND ORGANIC MOLECULES

An important development in the 1990s has been the growth in supramolecular chemistry, including the recognition that non-covalent interactions have an important role to play in all facets of chemistry. Chemical systems featuring these once occurred only in the realm of serendipity, but can now be achieved through careful design and synthesis. Non-covalent interactions involving metalloporphyrins, particularly where there is an interaction between an organic substrate and the metal center, form one extreme of :I continuum of organometallic bonding types spanning non-covalent interactions. agostic bonding, coordination of a-bonds (H-H or C-H), ?r-coordination, n-donor bonds, and fully covalent a-bonds. Close approaches of arene solvents to metalloporphyrins have been observed by crystallography. For example. Mn(TPP) crystallizes as a toluene solvate with a toluene solvent molecule lying on either side of the porphyrin plane. The dihedral angle between the porphyrin plane and toluene plane is 10.7 (reduced to 6.7 for one of the pyrrole rings). The average perpendicular distance between the toluene ring and the mean 24-atom plane of the porphyrin is 3.30 r\. One aromatic C-C bond of toluene approximately eclipses one N-Mn-N axis, with Mn. .C distances of3.05 and 3.25 A.196 There has been considerable effort invested in the preparation of a “bare” [Fe(Por)]+ cation, requiring a “lcast coordinating anion” as the counterion. Similar close approaches of arene solvates are seen in two examples. [Fe(TPP)]SbF(,C,HSF contains a Huorobenzene solvate with a dihedral angle between the porphyrin and arene planes of 7 . and average separation between the two planes of 3.30 p\.297The closest Fe. C(arcne) distance is 3.34 A. A complex of [Fe(TPP)]+ containing an even more weakly coordinating anion.

Transition Metal Porphyrin Complexes

313

[Ag(Br&B I 1H&contains a p-xylene molecule on each side of the porphyrin plane with dihedral angles of I3 and 5 The closest approach of a p-xylene atom to the mean plane of the porphyrin is 2.89 .&, and the closest Fe. C(p-xylene) distance is 2.94 A, about 0.2 A shorter than the sum of the covalent radii.2”x These examples blur the distinction between ligand and solvate, and in the two examples involving the [Fe(TPP)]+ cations, the closely approaching arene molecules may be playing a role in compensating for the positive charge on the cations. However. whether the M(Por)/arene interaction is driven by metal/arene “coordination” or porphyin/arene n/r interactions is still an open question. In one further example involving an iron porphyrin there is good structural evidence for heptane C-H coordination to iron.‘“” The complex Fe(DAP).heptane contains an elaborated “double A-frame” porphyrin, in which opposite pairs of phenyl rings in TPP are linked through the orthn positions by NHC(O)-I,4C6HJ-C(CFj)z- I ,4-C6HJ-C(O)NH straps, creating cavities above and below the porphyrin core. Each heptane molecule spans between two cavities on adjacent molecules, with close contacts between the iron atoms and the terminal methyl groups on the heptane molecules. The iron atom is displaced 0.26 A from the mean NJ plane toward the heptane, which is an indicator for five-coordination at iron. The Fe. C(heptane) distances are 2.5 and 2.8 r\, well within the 2.5-3.0 A range accepted for M. C agostic interactions. The structural data were supported by density functional theory calculations which gave Fe. C distances of 2.6X-2.70 A. This example is remarkable first because of the alkane coordination to iron( and second because it involves a fret alkane, not one covalently tethered to the molecule as is usually observed for agostic interactions.‘“’ Finally. a series of co-crystallates of fullercnes (C h,, and CT,)) with both freebase and metalloporphyrins show unusually short porphyrin/fullerene contacts (2.7-3.0 A) compared with typical rr-n interactions (3.0-3.5 A).““’ The fact that these close approaches are observed for both free-base and metalloporphyrins indicates that r-r interactions rather than metal/fullerene interactions are important in these examples. For example, H~TPPC~,(1~3tolucnc crystallizes in zig-zag chains of alternating porphyrin and fullerene molecules, with an electron rich 65 ring juncture lying over the center of the porphyrin ring. The closest porphyrin plane-fullerene interaction is 2.72 r\. The two metalloporphyrin cocrystallates are ZnTPPC71, and NiTTP.2C7,,.2toluene, which contain side-on C7() molecules with a carbon atom from three fused &membered rings lying closest to the pot-phyrin. The shortest Zn, ,C and Ni. .C distances in these structures are 2.X9 and 2.85 A. NMR evidence indicates that the interaction persists in solution. Overall, the interactions of the planar porphyrins with the curved fullerenes are important because they demonstrate supramolecular recognition without the need for matching a concave host with a complementary convex guest. These structures help to explain the function of the TPP-appended silica stationary phases used for the chromatographic separation of fullerenes: 700

314

PENELOPE

J. BROTHERS

( I ) Smith. K. M. (Ed.) ~c’oqdfwirf.r c/w/ Mrrtr//ol,r,~/,/~\,~.;~~~: Elsevier: New York. 1975. (2) Dolphin, D. (Ed.) T/w Porphyri~/$: Academic: New York, 1979; Volumes l-7. (3) Man\uy. D.; Lnnge. M.; Chottard. J. C.: Guerin, P.: Morlierc. P.: Brault. I).; Rougee. M. ./. C’/rc,ul. sot,., C/rrw. Co/rwrlfrl. 1977, 638. (4) Mansuy, I).; Lange. M.: Chottard. J. C.: Bartdi, J. F.: Chevrict-. B.; Wei\a. R. Aqq?ll: C/rt,nr., Iut. Ed. EqJ/. 1978, /7, 7x I. (5) Brother\. P. J.: Collman. J. P. Aw. f‘lwrr. Kc,\. 1986. 19. 209. (6) Setune, J. I.: Dolphin, D. (‘uu. J. C‘/wm. 1987, 65, ISO. (7) Guilard, R.: Lecomte, C.: Kadish. K. M. ,Sfw~~f. Ro~r~l. 1987, 64, 205. (X) Guilxd. R.: Kadi\h. K. M. Clwrv. Kcl: 1988, iiX, I I??I. (9) Kndish, K. M.: Smith, K. M.: Guilard. R. (Ed\.) T/w /Jo~~dr~~~i~~Htrd/x~~~X; Academic: San Diego. 1999: Volume 3. ( 10) Cheng. I,.: Chcn. L.: Chunf. H. S.: Khan. M. A.: Richter-A&k). G. B. f~,:~or~o,lruto//;[,\ 1998, (I I) ( I?) ( 13) I 14) ( IS) ( 16) (17) ( IX) ( 19) (20) (71 ) (2) (23) (21) (25) (26) (27) (2X)

Senfc. M. 0. /Ir~,yc,,r: Clw~., /pi. I+/. EII,~/. lYY6, 3.5 1013. Fehlner. 7: P. (Ed.) /r/o/actrro,l?c,/tr//j(, Chrrlri\/ry: f’h~um: New Ywh. IYK. Watanabe. Y.: Grow\. J. T. In E~r:ww.$ .j,r/ rd: Sigman II. S. Ed.: Academic: San Diego. I %I?_. Manwy. D. /‘((I-<, /~/J/I/. C7wrr. lY90, 62, 73 I. Meunier. B. (‘/w/u. Kw. lY92, Y2, I I II Sayer. P: Goutermun, M.: Connrll, C. R. ./. /\uI. f‘lrcw~. So<. 1982, /5, 73. Belcher. W. J.: Boyd. I! D. W.: Brothcra. P. J.: I.iddell. M. J.; Richard, C. E. F. ./. AUI. C/wr~. SW. 1994, I lh. X116. Belches-. W. J.: Breede. M: Brothel-s, P. J.: Richat-d. C. E. F. A,~,qcw. C‘hcwr.. Ijrr. /
(29)

Buchler. J. W.: De Cian, A.; Fixher. J.: Ilammel-~chmltt, P.: Wu\s, R. Clrcvrr. Hc,,: 1991. /21. IO5 I. (30) Ryu. S.: Whang. D.: Kim. H. J.: Kim. K.: Ywhida. M.: Hahimoto. K.: Tctwmi, K. /mq. C‘lrwu. 1997, .vL -lhO7. (3 I ) Srwchok. M. G.; Haud~altel-, R. C.; Mrrolu, J. S. Iraq. C’/zi/w i\c,ro 198X, I-l-!, 47. (32) Arnold. J.: Hoft’man. C. C. J. hr. C‘hr. Snc~. 1990, I /2. X620. (33) Arnold. J.: Hofl‘mon. C. G.: Dawwn. D. Y.: Hollander. F. J. OIXc//ro,,rc,ttr//i~..\ 19Y3, 12, 3615. (34) Schavericn. C. J.: Orpen. A. G. Irwq. C‘hru~. 1991, 30. 396X. (3.5) Schawrien. C. J. .I. (‘hew. Sot., CIICIII. Corr7mo7. lYY1, 4%. (36) Woo. Ia K.: Hays. J. A.; Jacobsen, R. A.: Day. C. L. f~r;~trr~~~,rier~~//ic~.s 1991, 10, 2 107. (37) Woo. L. K.: Hay\. A. J : Young, V. G. J.; Day, C. L.: Caron. C.: D-Sowa. F.: Kadish, K. M. (3X) Wang. X.: Gray. S. D.: Chen. .I.; Woo. L. K. /no,;q. c‘/w,u. IYYX, .<7. 5.

Transition

(3’)) (40) (4 I ) (12) (43) (54) (45) (46)

(47) (48) (39) (SO) (51) (52) (53) (54) (55) (56) (57) (58) (59) (60) (6 I ) (62) (63) (64) (65) (66) (67) (68) (69) (70)

Metal

Porphyrin

315

Complexes

Woo, L. K.; Hays, J. A. Irwr,q. Chew. 1993, .?2, 222X. Hays. J. A.; Day. C. L.: Youn,, ~7 V. G. J.: Woo, L. K. //nq. Chrrtr. 1996, .!S, 760 I. Gray. S. D.; Thorman. J. L.; Berreau. L. M.: Woo. L. K. Irrwq. C’lnw. 1997, 36. 278. Gray, S. D.; Thorman, J. L.; Adamian. V. A.: Kadi\h. K. M.: Woo. L. K. /r)or;g. C‘hwr. 1998, 37. I. Wang. X. T.: Woo, L. K. J. Org. Clwn. 1998, h.?. 356. Shibata. K.; Aida. T.: Inoue. S. Chern. Le/t. 1992, 1171. Kim, H. J.: Whang, D.: Kim, K.: Do, Y. Irwrq. Chwr. 1993, .<2. 360. Brand, H.; Arnold, J. J. Am. Chrm SK. 1992, I/4, 2266. Huhmann, J. L.; Corey. J. Y.; Rath. N. P.: Campana. C. F. J. O~gr~wrrw/. C/ton. 1996, 5/3. 17. Brand. H.: Arnold, J. O~~clno,rlc,rtr//ic,s 1993, 12, 3655. Ryu. S.: Whang. D.; Kim. J.: Yeo. W.: Kim. K. J. Cherr). Sot., /Itr/ro~ ‘7)w)r. 1993, 205. Ryu, S.; Kim, J.: Yeo, H.: Kim, K. /wig. Cllirn. Aml 1995, 22X. 233. Arnold, J. J. Am. Chrm. Sock. 1992, I/J. 3996. Kim. H. J.; Jung. S.: Jeon. Y.M.: Whang. D.: Kim, K. Clwrn. c‘own~n. 1999, 10.11. Brand, H.: Capriotti. J.: Arnold. J. O~xtr,~orllrttr/(i~s 1994, 1.j. 346’). Brand. H.: Arnold, J. Augew. C‘/rr~~~../,~r. Ed .!+,~I. 1994, 33, 95. Kim. H. J.: Juns. S.: Jean. Y. M.; Whang. D.: Kim, K. Chrrn. Co~rwt~~~~.1997, 2201. Shibata. K.; Aida. T.: Inoue. S. 7cr~tr/wdwn Lrtt. 1992, 3.3. 1077. Dawson. D. Y.: Brand. H.: Arnold. J. J. Am Chcm. Sot. 1994, /I(,, Y7Y7. Toscano, P. J.: Brand. H.: DiMauro, P. T. O~gc~nor~~etr~//ic~.r1993, I-?, 30. Colin. J.: Chewier, B. O/~trr?or,lcttr//ic,.\ 1985, 3. 1090. De Cian. A.; Colin, J.: Schappacher. M.: Rtcard. L.: Weisr. R. ./. Aw. Clzcwr. ,SOC, 1981, /03, IXSO. Collman. J. P.; Barnes. C. E.: Woo, L. K. Prw. /VU/. Actrtl. Sc;. USA 1983, X0, 7684. Collman. J. P.; Garner. J. M.: Woo, L. K. J. Am. Clwm. Sot. 1989, 111, XI-II.

(73) (74)

Tatwmi, K.: Hoffman, R.; Templeton. J. L. /~w,q. Clrcvn. 1982, 2/. 466. Berreau. 1,. M.: Young, V. G.. Jr.: Woo, L. K. /wt;q Chrrn. 1995, .?J, 34X.5. Jones. T. K.: McPherson, C.: Chen, H. L.; Kendrick. M. J. /wq. C/ri,n. Ar,to 1993, 206, 5. Brothers, P. J.: Roper, W. R. Chrw. Krt: 1988, XX, 129.1. Tatsumi. K.: Hoffmann. R. Inorg. Chern. 1981, 20, 377 I. Shin. K.: Yu. B. S.: Goff. H. M. frtorg. Chrnr. 1990, 2Y, 889. Balch. A. L.; Hart, R. L.; Latos-Graiynaki, L.: Traylor. T. G. J. Am C/wm Sot. 1990, 112, 7382. Arasasinpham. R. D.: Balch, A. L.; Olmatead. M. M.; Phillips. S. L. /wr,v. C/t;nt A&) 1997, 263. IhI. Balch, A. L.: Lam\-Gra%yhski. L.: Nell. B. C.: Phillips, S. L. Irtorg. C/tern. 1993, .12, 1124. Setsune. J. I,: Ishimaru. Y.; Sera, A. .I. Chrrrr. Sot.. Chem. Cmrn~~r,~. 1992, 32X. Jame\, C. A.: Woodruff, W. Irqq. C/ti)n. Amr 1995, 22Y, 9. Takeuchi. M.: Kano. K. Oy~trrlor,~rrtr//ic~s 1993, 12. 2059.

(75)

Guilard.

(71) (72)

R.; Lagrange.

G.: Tabard, A.; Lanqon.

D.; Kadish,

K. M. /rw,y.

Chrrn. 1985, 24, 3649.

(76) Lexa, D.: SavCant. J. M.: Wang, D. L. O,~~trr~~,~rlrtc~//i~,s1986, 5. 1428. (77) Gueutin. C.; Lexa. D.; Saw%nn. J. M.: Wang. D. L. O~~“““‘nc,/tr//ics 1989, 8, 1607. (78) Lexa, D.; Sov&mt. J. M.; Su, K. B.: Wang. D. L. ./. Afn. Chrrn. SOC,. 1988, I IO. 76 17.

(79) I,exa. (80)

D.; Sav&mt. J. M.: Su, K. B.: Wang, D. I.. J. Am. C/m~. ,5x. 1987, /OY, f~465. Lexa, D.: SavCant. J. M.: Schafer. H. J.: Su, K. B.; Vering. B.: Wang, D. L. ./. Am. C/w~r. SOCK.

(81) (82)

DeSilva. C.; Czarnecki. K.: Ryan, M. D. I~,x. Arasasingham, R. D.; Balch, A. L.; Cornman,

1990,112. 6162. Ch;rn. A~cl 1994,226, C. R.: Latos-Grajynakj,

1989,111.4357. (83)

Li. Z.: Gaff. H. M. Irrrq.

C/nwr. 1992, 3/,

1547.

195. L. J, A,,,. c/,~w~.

,k.

316

PENELOPE

J. BROTHERS

(84) B&h. A. I,.: Rcnner. M. W. /IIC~. C/IC~I. 1Y86, 2.5, 303. (X5) Guilard, R.: B6i\aelier-Cocolio\. 6.: Tahard, A.: Cocolio\. P.: Simonet. B. /juq. C‘/wrt~. 1Y85. 24, 250’). (X6) Lanpn, I).: Cocolio\. I’.: Ciuilard. R.: Kadish. K. M. .I A/u. C‘Iwu. .SOC. 1984, /Oh, 4177. (X7) Batch. A. I,.: Cornman. c‘. R.: Sd’nri. N.; I,ato\~(;rai4ri~hi. L. O~%ccf~o/lrcr~~//i~,.\1990, (1. 7120. (881 Tahiri, M.: Dopprlt. P.: Fiwhcr, J.: Weir. R. /~w;s. (‘/w/u. 1988, 27, 2X97. (X9) Tahard. A.: Cocolio~. P.: Lqrange. G.: Get-al-din. R.: Hubxh, .I.; I.ccomte. C.: %xcmhow~itch. J.: Guilwd. R. I~rrq. C/w,rr. lY88, 27. I IO. (90) Kadish, K. M.; Tatxwd. A.: L re, W.: I.iu. Y. H.: Ratti. C.: Guilard. R. /uoJ:~, (‘/wx 1Y91, .iCl. 1542. (Y I) Kndi~h, K. M.: D’Sowa, F.: Van Cacmelhecke, l;.; Villas-d. A.: Lee. J. I>.: Tabard. A.: Guilard. R. /,wq. (‘lw,7. 1993, -12. 3 17’1. (92) Kadish. K. M.: Van Carmclbcche. E.; G~elctii. ti.: Fukwmni. S.: Miyamoto. K.; Suenohu. ‘f.; Tahard. ,A.: Guilartl. R. Iuo,;q~ C/wu~. 19Y8, .{7. 1759. (93) Kadish. K. M.: D’Sou~a. F.; Van Caemelhcchc. E.: Bwla\. P.: Vogel, E.: Auhauloo. A. M.: Guild. R. /uo~;~. C’lwur. 1994, .13. 4474. (94) Kadish. K. M.: Tahard. A.: Van Carmelhcckc. E.: Adauloo. A. M.: Richat-d. P.: Cuilard, R. hrorq. C‘hr. 1998, .<7. 6 16X. (95) Kadish. K. M.: Van Caemelheckc. E.: D’Sou/n. F.: Medtorth. c‘. J.: Smith. K. M.: T;lhard, A.: Guilard, R. Or;~~~,~oi~rrto//;~,\ 1993. 12, 24 I I. (96) Kadiyh. K.: Van Carmelhccke. E.: D‘Sowa. F,: Medt’wth. C. J.: Smith. K. M.: ‘l%nt-d. A.: Guilard. R. /uoI:$. C‘/w~u. 1995, .<-1. 2983. A. X.: Wiegharth. (97) Vogel. E.: Will. S.: Tillin,. (7 A. S.: Nrumann. I..: lxx. J.: Bill. E.: Trautacin. K. Ail,pew. C/IPII/.. /I?/. f?/. t‘,,y/. 1994. .j.?. 73 I, (OX) Van Caemelhecke. E.: Will. S.: Autret. M.: Adamian. V. A.: Lex. J.: Gisselhl-echt. J. P.: Gross. M.: Vofel. E.: Kadlah. K. IIIOI;~. (‘lww. 1996, 35, I X-1. (99) Doppelt. P. //ro,;i’. C/ww. 1984, 2.3. 4009. (100) Balch. A. L.: Olm\teatl, M. M.: Snl’ari. N.: St Clam!. ‘1. N. Ifrcq. Clwr. lYY4, .(.i. 2815. (101) Olmstcad. M. M.: Chrng, R. J.: Batch. A. L. //ror~. (‘lrcw. 1982, 2/. 3 133. (102) Chcvricr. B.: Wei\\. R.: lx~ge. M.: Matlwy. D.: C’hottard, J. C. ./. ,1/n. Circv~r. SOC,. 1981, /(Ii. 2800. ( 103) Bdch. A. L.: Rcnner. M. W. ./. Aur. (‘/I~I. .Sor,. 1986, /OK. 603. ( 104) Belch. A. L.: La Mar. G. N.: Latos-Grniyri\hi. L.: Renner. M. W. /rw;q. C/wu~. 1985, 24. 7432. (105) Late\-Gratyriaki, L.: Wyslouch. A. /rw;q. C/ri/u. Adu 1990, 171. 205. 1985. 24. ll4.i: th) Lavnllw. ( 106) (a) Kuila. I).: Kopclow, A. B.: Lavallee. 1). K. //ro/:+C/w,~. D. K. T/w C%Cu~i.t/q trd Biodrerui.strv of N-.Sdurir~c~d Porph~~-ir~v: VCH Verlapagc\ellschaft: Weinheim. 1987. (107) Song. B.; GolT, H. M. Iwr;~. C/rim. krtr 1994, 226. 23 I. ( 108) Riordan, C. G.: Halpern. J. /u~q. Clriw. A&r 1996, 2-13. IO. ( 109) Bnlch, A. I.. /,wg C/?i,u. Ar,rn 1992, IYX-200. 297. (I IO) Araaahingham. R. D.: Belch, A. L.: Latos-Graiyr’hhi, I,. .I. A/u. C/~/II. SOC. lY87, IOY, 5816. (I I I) Araaasingham. R. L).: Cornman. C. R.; Balch. A. L. .I. Au?. C‘l~rru. 5x1 1989, I I I, 7800. (I 12) Al-aasinpham. R. D.: Bulch. A. L.: Hart. R. L.: I.atos-Gt-a/:yri\ki. L. J. Am. Chew. Sm. 1990, I/2. 7566. ( I 13) Cocolio. P.: Laviron. E.: Guilard. R. ./. O~;~trww~/. C‘hcwr. 1982, 228. C?Y. (I 14) Arafa. 1. A.: Shin. I<.: Gaff, H. M. .I Aw. Clwru. .Eoc,. lY88, /IO. 5228. (I IS) Gueutin. C’.: Lexa, D.: Momcnteau. M.: SavCunt. J. M. ./. Am. Clrrrx SW. 1990, I I2. 1874. ( I 16) Hammouche. M.: Lcxa. D.: Momenteau. M.: Sav&mt. J. M. J. A m Clrcw. Sot,. 1991, / 13. X355. (I 17) (a) Bhugun, 1.: Lexa. D.: SavCant. J. M. .I. Asr. C/w/u SOC,. 1994, I/h, 501.5. (b) Bhugun. I.: Lena. D.: Saw&t. ./. M. ./. Am. C‘lrrm. Sot. 1996, I IX. I76Y.

Transition

( I IX) (I I’)) ( 11-0) ( 171 ) (I 22) (123) ( 123) ( 125) (I 26) ( 127) ( 128) ( 129) ( 130) ( I3 I ) ( 132) ( 133) (I 33) ( 135) ( 1%) (137) ( 138) ( 139) ( 110) ( I3 I 1 ( I-l?-) ( 143) (I 14) ( I-15) (1%) ( 147) (14X) (139) ( 150) ( IS I) ( 152) ( 153) ( 154) ( 15% (1%)

Metal

Porphyrin

317

Complexes

Kim, Y. 0.: Gaff. H. M. J. Am. C/xw. Sot. 1988, / 10. 8706. Song. B.: Gaff. H. M. /rw/;~. Clwrl. 1994, 33. S979. Beck, W.: Knauer. W.: R&l. C. Ayyw, Chrm.. Ior. Ed. 01gl. 1990, 2Y, 3 IX. Manly. D.: Lecomte. J. P.: Chottard, J. C.; Ba~~oli. J. F. Inor,~. C/w~z. 1981, 20. 3 I 19. Goedken. V. L.; Deakin. M. R.: BottomIcy. I*. A. J. C/xw. Sock., C‘lrcw~. Com/rr~m 1982, 607. Kienaat. A.: Bruhn. C.: Homhor g, H. Z. Anor: A//g. C/MI. 1997, 62.1. 967. Kiena\t, A.: Homborg. H. Z. AIM: A//,q. Clrcm 1998, 624, 107. Galich. L.; Kienaht. A.: Hiickstiidt. H.: Hornborg, H. Z. Aw1: A//g. Chew. 1998, h2J. 1235. Rcwi, C.: Gocdken. V. L.: Ercolani. C. ./. C/I~I. Sot... C/~/U. C‘~UI/~~I/I. 1988, 36. Ercolani. C.; Gurdini. M.: Goedken. V. L.: Pennesi. G.; Roasi. G.: Ku\w, U.; Zanonato. P. Irloq. Clwrn. 1989, 2x. 3097. Ziegler. C. J.: Su\lick. K. S. J. AUI. Chem. Sm. 1996, I IH. 53Oh. Ziegler. C. J.: Suvlick, K. S. J. Or~curorrw/. Chrr. 1997, 528, X3. Balch. A. L.: Ghan. Y. W.: Olmstead. M. M.: Renner. M. W. .I. OI-,q. (‘/~/II. 1986, .5/, -165 I. Manuy. D.; Battioni. J. P.: Lavaller, D.: Fischer, J.: We& R. Irroyg. Clrrw. 1988, 27. 1051. Balch. A. L.: Chan. Y. W.: La Mnr, G. N.: Lntos-Graiyriski. L.: Renner. M. W. /~ror~. Clw~r. 1985,24. 1437. Balch. A. L.: Cheng. R. J.: Ian Mar. G. N.: I,ato+Gt-aiyli\hi. L. Irwq. C‘lrw. 1985. 24. 265 I. Artnud, I.: Gregoire, N.: Battioni. J. P.: Dupre. D.: M;mwy. D. ./. AIU. C‘/~UII. .Soc, 1988, I II). 8711. Artaud. 1.: Gregoire. N.: Leduc. P.: Mansuy, D. J. Am Ckm. Sock. 1990, 112. 689c). Sctwne, J. 1.; lida, 1:: Kitao. T. ~r~thrtlwr~ L?!r. 1988, 29, 5677. Wolf. J. R.: Hamaker. C. G.: D,jukic. J. P.; Kodadek, T.; Woo. L. K. ./. A~II. C‘lrcv~~.So<,. 1995. l/7,9193. Simmoneaux, G.: Hindre, F.; Le Plowennec. M. Irwr;~. C/wr~. 1989, 28. 823. C&e. C.: Legrand, N.: Bondon, A.: Simmoneaux, G. /w,;y. Chi,rr. Acftr 1992, 1Y.i 73. Walker. F. A.: Nasri, H.: Turowka-Tyrk. I.: Mohnnrao, K.: Watson, C. T.: Shohhireb. N. V.: Debrunner. P. G.: Scheidt. W. R. J. Am. C/rem. Sk. 1996, I IX. I2 109. Camenrind. M. J.: James, B. R.: Dolphin, D. ./. C’/~IU. S’w.. Chc~r. C‘~~IUIIUJI. 1986, l 137. C‘ollman. J. P.: Brother\. P. J.; McElwee-White. I,.: Row. E.: Wright, L. J. ./. AJII. (‘/w~l. .Soc~. 19x5, 107. 4570. Collman. J. P.: Brothers, P.J.: Mc-Elwee Whltc, L.: Robe, E. J. Am. Clrcw. .W. 1985, 107. 6 I IO. Collman. J. P.: Prodolliet. J. W.; Leidner. C. R. ./. Am. L‘hr. Sot. 1986, /OR, 29 16. CoIlman. J. P.; McElwee-White, L.: Brothers. P. J.; Rose. E. J. Am. Chrm. SK. 1986, /OX. 1332. Camewind. M. J.: J;rmc\. B. R.; Dolphin, D.: Spurapany. J. W.: Ibers. J. A. Irrog. c‘lww. 1988, 27. 3054. Sishtn. C.: Ke, M.: James, B. R.; Dolphin, D. J. C/W~I. Sock.. C/wrn. ~‘o~w~~u~ 1986, 787. Kc, M.: Sishta. C.; Jame\, B. R.; Dolphin, D.: Sparapany. J. W. /IIO,-~. C/w~r~. 1991, .1(). 476h. Scylcr. J. W.; Safford, L. K.; Leidner, C. R. Inoq. Chew. 1992, .(I, 4300. I,eung, W. H.: Hun. T. S. M.: Wang, K. Y.: Wang, W. T. ./. C/ww. So<,.. /)tr/rort ‘rw~,\. 1994, 2713. Ke. M.: Rettig, S. J.; Jnmes, B. R.: Dolphin. D. J. C/tcw. SW.. C/WUI. C~~WW~L 1987. I I I(). Alexander. C. S.: Rettip. S. J.; James, B. R. Or,~o,~r,,,~rttr//i~~,\ 1994, I-3, 2532. Seyler. J. W.; Leidner. C. R. J. Chw. Sot,., C/wu. C~~~~IWI. 1989, I793. Seylcr, J. W.; Leidner. C. R. Irwr-g. C‘hrw. 1990, 2Y. 3636. CoIlman, J. P.; Rose. E.: Venburg. G. D. J, Chrm Sot.. Chew. Cmmw~ 1994, I I Collman, J. P.: Ha. Y.: Wagenknccht, P. S.; Lopez. M. A.: Guilnrd. R. ./. ,Aw. C/ww. ,~w. 1993,

(157) Scylcr. J. W.; Fanwick, P. E.: Lcidner. (1.58) Seyler, J. W.: Safford, L. K.: Fanwick.

C. K. //ror,y. Chrr~. 1990, 2Y, 1021. P. E.: Leidner. C. R. /wt;q. C/wr~. 1992,.
1545.

318

PENELOPE

J. BROTHERS

( I SY) Hedge. S. J.: Wrrnf. I,. S.: Khan. M. A.: YOU,. (7 V. G. J.; Richter-.Addo.

G. B. (‘//
1996,22X3. (160) ( I6 I) ( 162) ( 161) ( 16-I)

( 166) ( 167) (I 68) ( 169) (170) ( I7 I ) t 172) ( 173) t 17-t) ( 175) ( 176)

Seyler. J. W.: Fanwick, P. E.: Lcidnrr. C. R. /r~o,;q. (‘hc~rr. 1992, .i/. 3699. Rajapukx, N.: Jama. B. R.: Dolphin. D. Cox ./. C//rf~t. 1990, hS. 2274. Maruyama. H.: Fu,jiaara. M.: Tanaka. K. C‘hv~r. f.c,/r. 1998, 805. Collman. J. P.: ROSC. E.: Venhurg. G. D. ./. C/I<,/,,. So<... C‘hr,,r. C~,,~r,,~rr,r. 1993, 934. Galardtrn. E.: Le Mnux. P.: Toupet, L.: Simmoneaux. G. O,~~tr,fo,,rc,trr//;[,,\ 1998, 17. S6S. Balch. A. L.: Ghan. Y. W.: Olm\tead. M. M.: Renncr. M W.: Wood. F. E. ./. AJU. C‘/rr~r~. .%x. 1988, 110, 3x97. Woo. 1,. K.: Smith. D. A. O,~trr~or,,rrr,/lic,\ 1992, I/. 2313. Woo. 1.. K.: Smith. D. A.: Younf. V. G. O,n~,r~~,r,,ct~,//;(,\ 1991, 10. 1977. Djuklc. J. P.: Smith, 1). A.; Young. V. G.: Woo. L. K. O,~~c/rl~,rlrc,ttr//j~.,\ 1994, 1.f. 3020. D,jukic. J. P.; Young. V. C. J.: Woo, L. K. Ol;~i~,ro,rlc,/cl//i~.\ 1994, 13. 39% Smith, D. A.: Reynolds. D. N.; Woo. I.. K. ./. ,4frr. (‘hr~~. Srx,. 1993, l/S. 2.51 I. Gala-don. E.: Lcmauu. P.: Simonneaux. G. C/I<,UI. C‘~,/nrn~n. 1997. 927. Galardon. E.: Roue. S.: Lcmaux. P.: Simonneaurc. G. Tc,tvtr/r~t/,n~ Lrtt. 1998, .?Y. 2333. Lo. W. C.: Chr. C. M.: Chenf.. K. F.: Mah. T. c‘. I+‘. Chc,,rr. C’o~,r,,r~/r. 1997. 1205. Frauenkron, M.: Berkcsvzl. A. ~>~u/I~
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Brothel-\. P. J. PuI,~. /mq. Collmnn. J. P.; Hutchison.

(179)

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(IX()) (181) ( 182) ( 183) ( I X4) ( 185) ( 186) (187) ( 188) ( I X9) ( 190) (I9 I ) (192) t 193) (lY3) (195) (196) (197) (198) (199) (200)

Che,~. 1981, 2K. I. J. E.; Wagenknecht. P. S.: Lewis, N. S.: Lope/.

M A.; Guilard.

R. ./.

Transition

Metal

(20 I) Will. S.: Lex. J.: Vogel. E.: Adami;rn,

Porphyrin

319

Complexes

V. A.: Van Cacdbrcke.

E.: Kadish.

K. M. Iwi;q.

C‘lrcw~.

1996,35. ss17.

(221 ) (221) (223)

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(22-I)

Sctwne.

(203) (203) (205) (206) (207) (20X) (209) (2 IO) (?I I) (2 13) (2 13) (2 I-+) (215) (2 16) t2 17) (21 X) (2 19) (720)

J.: Tcheda. H.: Ito. S.: S;I~IO, Y.: I\hinlnr-n,

Y.: Fuhuhara.

K.: Kitao. T.: Adachi.

1‘. /wry.

(725) (3%) (127) (228) (2’7% (130) (23 I ) 1131) (133)

Schune. J.; T;\hcda. H.: Katakanu, Y. C/wi. Le/r. 1998, 527. Setwne. J. I.: Saito, Y.: I\hitnaru, Y.: Ike&. M.: Kitao, 1‘. Hi,//. Clrcw. Sock. .//,,I. 1992. c’I.i, 639. Watanube. J.: Serwne. J. O,go/to/rlcttr//;~‘\ 1997, lh. 3679. Wayland, B. B.; Woods. B. A. .I. (‘lrcwr. Socc. Chriir. C‘o/rw~rr,/. 1981, 700. P;tone\u R. S.: Thomas. N. C.: Halpern. J. J. Am Chrm. 5’0~. 1985, 107. 1333. Callot, Ii. J.; Metr, F.: Piechoki. C. ~~/dc~du~r~ 1982, 7365. Del Row, K. J.; Wayland. B. B. ./. (‘hcwr. SOCK..C/w,,i. C‘o/~u~~~rr~. 1986, 1653. C’trrnillon. J. L.: Anderwn. J. E.: Swihtah. C.; Kadid~. K. M. J. Am. Clrru~. SOC,.1986, /Oh’, 7631. Kadi\h. K. M.: C’omillon. J. L.: Mitaine. I’.; Dwg. Y. J.: Korp. J. D. Iuor;q. C/~OI. 1989. 28. 2354. (73-1) T;lhcnah;l. A.: Syal. S. K.; S;IU&I. Y.; Omura. ‘T’.: Ogwhl. H.: Ywhida, Z. I. /\u~I (‘rv.r/. 1976, (23% (236) (237) (23X) (9-39) (240) (211)

I’lei\cher. Iliich\tidt. Andcl-hon. Anrler~on, Gra\\. V.; Lexn. I).: (;ra\\, V.:

E. B.: Lavdlee. D. J. Am. C’lw~~r. SOC,.1967, 89. 7 132. H.; Hornborg. H. Z. Awr: A//g. Chu. 1998, 624. 980. J. E.; Yao, C. L.: Kadi\h, K. M. /w/;q. C/wn. 1986, 25, 718. J. E.: Yao, C. L.: Kadidl. K. M. J. A/jr. C/wm SW. 1987, 100. IlO6. Lexa. D.; Momcnteau, M.: .S:n@ant, J. M. J. Am. (‘km. .k. 1997, I/Y, 3.536. Gas\. V.; Sa\&nt, J. M. O,~tr,,or,rrrtr//;~~.\ 1998, 17, 2673. Lexa. D.: SavC;wt, J. M. J. Am. C‘lrcr~r. Sm.. 1997, //Y. 75X.

320 (242) (143) (244) (245) (736) (247) (24X) (249) (250) (25 I 1 (2.52) (253) (2541 (255) (2%) (257) (158) (2SY) 1260) (261) (262) (263) (764) (265) (266) (267) (76X) (26’)) (270) (27 I) (272) (273) (27-l) (27S) (276) (277) (378) 1170) (280) (281) (2X1) (283) (2841 (285) (2X6) (2X7) (28X) (2X0) (290) (29 I )

PENELOPE

J. BROTHERS

Grodkowski, J.: Neta. C: Abdallah. Y.: Hnmbrighl. P. ./. P/III\. Clww. lYY6, 100, Anderwn. J. E.: I.iu. Y. H.: Kadish, K. M. /rwt;v. (‘/w/n. 1987, 26, 4 I 73. Kadihh. K. M.: Arwllo. C.; Yao. C. I.. O,;~ci~,o~,rrrct//;~,\ lY88, 7. ISXj. Wayland. B. B. &/v/w/w/ lY88, 7. 1545. Waylnnd. B. B.; Van Voorhees. S. L: Wilher, c‘. /~I~~~~~:. (‘/IPIJI. 1986, 25, 4039. Ni. Y.: Fivgcrald. J. P.; Cxroll, P.: Wayland. Ii. B. /~~q. C‘hcw. lYy4, .1.?, 202Y. Del Ro\ri. K. J.: %han f. X. X.: Wavland, B. B. .I. O/;~curo,,rrt. C‘lwr,r. lYY5, 50-1. 47. Wayland, B. B.: Van Voorhecs, S. f>.; Del Roei, K. J J. Am. ('k/r/. .k. 19x7, /(N, hS 1.3. Wayland. B. B.: Powmk. G. O~Xtr,~o,,rrt~,//;~~, lYY2, I/. 3534. Bunn. A. G.: Wayland. 13. B. ./. A,i,. Clrur~. S,w. IY92, I I-I. 6917. Del Ros\i, K. J.; Wayl:md. B. B. J. Am. (‘lrrm. Srw. 1985, 107. 7Wl. Sherry, A f-I.: Wayland. B. B. J. 4111. C'/w~~~..Sw IYYO, //2, 1250. Wayland. B. B.: Ba, S.: Sherry. A. f!. ./. /I/II. C/wu~. .SOC.IYYI, 113. 5305. Wayland. B. B.; Ba. S.: Sherry. A. E. /utq C’/rc/r~. lYY2, .i/. 14X. Zhang. X. X.: Wayland. B. B. J. Am. ~'lrcw. .SOC IYY4, l/h. 7x07. Wayland. B. B : Woods, B. A.; Coltln. f3. I_. Ol;~ri,,r,,frcr~r/lic , 1986, 5, 105’). Coffin, V. L.; Brenncn. W.; Waylaid. B. B. .I. ,Iur. Chew. .Sw 1988, /IO. 6063. Waylund, B. B.: Sherl-y. A. E.; Povmih. G.: Bunn. ,A. C;. ./. Au,. C/ww. SOC. lY92, 114. 1673. Wayland. B. B.: Shcrl-y. A. b.: Coffin, V. 1.. ./. (7w1u. .SCIC,.,(%OUI. Co~~w~uu. lY89, 662. Sherry. A. E.: Wayl;md. B. B. J. Am. ~‘/rw~. .SCK. 1989, 111. 5010. Zhang. X. X.: Park\. G. F.; Wayland. B. B. J ,4m. C/NI~. SOC,. lY97, I/Y, 793X. Povmih. Ci.; Carroll, P. J.; Wayland. B. B. O~:rcoro,,lc,rci//~~,., 19Y3, 12, 13 IO. Aoyamcr. Y.: Yoqhida, T.: Sahurai. K. I : Ogoahi, I I O,:i’~~,~r,,lic,ro//;~,,\ 1986, i. 1(,X. Zhou. X.: I>i. 0.: Mah. ‘I‘. C. W.; (‘ban, K. S. l,/rq. C‘/r/,i,. A<‘/(/ 1998, 270. SSI. Zhou. X.: Wang. R. J.: Xuc. F.; Mah. T. (‘. W.: C‘han. K. S. J. O~~~c~m~wr. C‘hw. 1999, &SO, 22 Aoynma. I’.: Tanaha. Y.: Ywhlda, T.; TOI. tl.: Ogo\hi. Ii. J. f~~~~~~~wrwt.C‘hrr. 1987, .?ZY. 25 I Aoyama. Y.: Yamagishi, A.: Tanaha. Y.: Toi. H.; Ogo\hi. H ./. A,rr. C’lw~~. Sw. 1987, IOY, 4735 Mi/utani. T.; Ueaha. T.: Opshi, H. O,~~[~/~l,,l~rttr//;[,\ lYY5, 14. 341. Wayland. B. B.: Balhu\. K. J.: Farno\. M. D. O,.i’cl/ro,,~crr~//ic,.\ 1989, Y, 950 Maxwell, J.: Kodadeh. T. O/~~/,rr,,r?crft//~~..\ 1991, II), 4. Maxucll. J. L.: Brown. K. C.: BarUq. II. W.: Kodadch, ‘I’. .S~,icu~c IYY2, 2.~6. 154-i Bwtley. f). W.: Kocladch. T. .I. ,ZUI. C‘lwu. SOC, IY93, I li. 16.56. Brown. K. C’.: Kodadch. T. .I. AUI C‘/wu. Sw IY92, 111, X336. O‘Mallcy, S.: Kodadeh, T. 7i,t /.r//. 1991, .Q ?.t4S. Maxwell. J. la.: O’Mallcy, S.: Bro~.n, K. (‘.: Kodadeh. T. O,~orlo,r,c,ttr//ic., 1992, //. 645. 0’ Mallcy, S.: Kodadch. T. O/gci,~~~,~~c/~~//i~~.v 1992, I I, 22Y9. Hayuhi. I‘.: Kate. T.: Kaneho, T.: Aw. 11; Qwhi. tt. J. Oqtrmmrt. C‘hrm. 1994, 47.1. Bowhi. I’.: I.icoccia. S : f’aolc\w. R.: ‘&liateta, f? O,~so,~c”j,rt~,//f~,,\ 1989, X. 330. Whans. I).; Kim. K. Auo C’w.\.t. IYYI, (‘47. 2547. Kadi\h. K. M.: Hu, R.; Boxhi, T.: Tagliate‘;~a. f’. /,rtu;q:. (‘IICUI. IYY3, .<2, 7Yc)h. T\e. A. K. S.: WU. B. M.: M&. 7‘. c’. W.: Ghan. K. S. ./. Oq:c/now. c‘/rt,f?r. 1998, 5&y, 157. Licocua. S.: Paolesse. R.: Boxhi. T A~tr Cf;v.,1. lYY5, CS/. X33. Jane\. N. L., Cwt-011. I? J.; Wayland. B. B. O,:y~/i~l,,j,c,to/lir.J 1986, 5. 33. Lux. D.: Dnphnomili. II.: Coutolelo\. A. G. /‘o/~/wc/n,u 1994, /3. 2367. Coutsolelo. A. G.: Lux. 11 ~o/~/rrt/,-cur lY96, /i, 705. Daphnomlli, L).: Scheidl. W. R.: Zajicch. J.: Coutwlelos. A. G. /uop C‘heur. 1998, 37, 3675. Che\I-w. B.: Weiss, R. .I. /Iru. C/w)?. Socz 1976. YX. 2YXS. Chnn. Y. W.: Renner, M. W.; Balch. A L O,~~~,r~,,/r~~,r[l//f[,.\lY83, 2. I XXX. Chmieleu\ki, P, J.: L.;lto\-Graiyti\hi. I.. //ro~:~. C‘lrco~. 19Y2, .1/, 5231. Chmielewshi, P. J.; I.aros-(;raiyti~hi. 1.. /w,;q. ~‘/w~~. 1998, -37. 1179

Transition Metal Porphyrin Complexes (292) (293) (291) (2Y5) (296) (297) (2YX) (299) (300)

321

Chmielewski, P. J.: Latos-Graiy&ki, L. Itwr.,g. Clw~. 1997, 36, X40. Takao, Y.: T:tkedn, T.; Watanabe, J. Y.; Setaune. J. 1. O~~clr~o,rtrrtr//ic,~1999. IH. 29%. Inoue. S.: Murayama, H.: Take&, N.; Ohkatw, Y. C‘lrrw. Left. 19X2, 3/7, (a) Murayama, H.: Inoue. S.; Ohkatw. Y. C/IC~I. Lcfl. 1993, 381 (h) Inoue. S.: Nukui. M.: Kojima. F. Clwn~. Lutt. 1984, 6 19. Kirner. J. F.: Reed, C. A.: Scheidt. W. R. J. Am C/rem. .'h. 1977, YY. IO93. Shelley. K.: Bartczak. T.: Scheidt, W. R.: Reed. C. A. /wr;g. Clrc,~~.1985, 24. 4325. Xie. Z.: Bau. R.; Reed. C. A. Aqw: Clro~, I/U. Ed. DI,~/. 1994, j.3, 2433. Evans. D. R.: Drcrvet\kaya. T.: Ban. R.: Reed. C. A.: Boyd. P. D. W. .I. &jr. C/~/II. Sot. 1997. I IY. 3633. Boyd, P. D. W.; Hodgwn, M. C.: Rickortl. C. E. I-.: Oliver. A. G.: Chaker. l..; Brother\, P. J.: Bolskar. R. D.; Tham. F. S.; Reed. C. A. ./. Am. C‘lw~r. Sot,. 1999, /2/.

Index A

osmium porphyrins. 273-27-l truthenium porphyrin\, 273-27-l Alkyne porphyrin\, 2?&237 Alkynyldisilane\. X AlkynylRuoro~itane. 2I Alkynylpoly\itaner medyl group addition. I2 thermolytic reaclions. Y t -Alhynyl polysilanes. h Allenc, I Altytchloro\ilunes in alkylation\

calculations. CzH4Si iwmerh. 3 Acetylcne5. M-67 Acrylatea. 290 Adamantyl group. 186 Alkene complexes cobalt pwphyrins. 2X%293 cycloprop3natioll. 263. 27G277, 307-3OY o~nium porphyrin\, 271-271 trmhcnium porphyrin\, 271-271 Alhenylsilaneh. I36 Alkylntion. ,wc’ Fricdal-Crafts alkylalion Alhyl comt~lesc~ cobalt porphyt-in5 Co-<‘ bond encrgie\. 2X3-285 I’xtureh. 282Z283 I-edox chemistry and electrochanistrq, 2X5-286 5yntht3i\ and Ireactivi~y. 2XOL282 iridium porphyrins, 2052Y8 or-ganoiron porphyrins Fe-C bond homolysi\, 255-256 Fe-to-N migxtion. 2S4P2SS 5ilyl and ~tannyl compIcxc~. 259 \midl molecule inwrtion, 2.56-2.58 \ynthcbi\ and properties. 246-254 owiiun~ porphyrin.5. 266-273 rhodium pwphyrins. 2YSP2YX ruthenium porphyrin\. 26&77i Alkylclln~ocnt-ko*yl~t~~, 7&7S Alkyl group\ in nuclcophitic carhenes, 186 wtxlitured henrenes. I61 Alhplidene porphyrin\, 262 Alhylidyne groups clea\a~e. 73 face-capped lrinuclear clusters, X6 in group h-group Y cluster\. 72 Alkyliron porphyrins, 256-2.57 Athync-hridgcd clusters, XX Atkync comptexe\ cobalt pal-phyt-ins, 29 I-2Y3 group erhylalumin~ttion. 230 with gwup h-group Y clusters, 72 cwxq, migration, I2 I Ah iuirio

somatic hydrocarbons. I SOb I :iS t’cl-I-occne. t S.% IS8 for hcnrcne poty:dkglation. IS3 Allytdichloro\ilane. IS I Allyl\il;me~, l-16-137. IIY Altyttrichloro~il;Ines. IS1 Aluminum chloride in aromatic compound alkylation. t 6S- I f)Y in hcwene nlkylation. 1.50-l SS in ferl-occnc alhy lation. IS6 in Fried;~l~Crd~~ alkylatiorls. 137-l 4X Amination, arylchloride\. 2 I S-2 IX Ani\ole, 16-t 6S Arena Fried&C~-afis alhylnlion~, 13X metnlloporphyrin inleraction, 3 I:! Aromallc compounds. alkylation. 15X-t SC). I hS- t 6s Aromatic Hyde-wnrbon~, alhylation. 150-l SS Arytamidop~~ltadiurn. 216-2 t 7 Arylhoronic acid<, 20X-2 IO Arglhromide\ aminutions, 2 I6 cro~woupling reaclim~s. 2 12-2 t 3 Al-ylchlorides amination. 2 t S-2 I X Cl.O\h-CoUplinf Kumxta rcac~mns, 2 I I-2 IS Swuhl rcacIions. 20X-2 IO Aryl-cobalt porphyrins. 286 Aryl complcw~ cohnlt porphyrin\ Co-C bond energies. 2X3-285

323

324

INDEX

c

B 13UlLLW3 alhytatlon

atkyl-wbstiwlcd henxne\, l6& t 65 M Ith altytchlorosilane\. ISOLISS with (lu-chloroalkyl)\ilanes. 177-l 7X uith (dichlot-oathyl)chloro~ilanca, t 70 with ((,,.crJ-dichloroalkyI)~itancs, I hY halogcll-suhstttuted benxncs. 11’). t S.3. I70 monosuhstltuted benoznc\, t 3’) with (trichlol-omcthyl)silnne\. I73 from decomposition reaction. I75 derivative potyalkylation. IS1 polyalhylalion, ISY~lhl Irhodium porphyrin reaction\, 306 substituted. reaclivity, IS3 tran\alkytationh. I SO Benqt chtoridc in atkylntion. IIY in ~lectrocnrboxylation. 2X6 Biphenyl. alkylation, 172. 176 I.%Bi\l I ~~~da~nantyl)imida/~~l~-2-yiidcne. I87 Bis(~yclot~~tlf~~dirnyl) complcxc\, 332

Catorlmrtrq. nuctcophilic cxhenes. IX&l XS Cal-hcne comptcw with coball porphyrins, 282 with it-on porphyrin\. 2SY%263 Iwc)anatc addition. 15~26 with wmium porphyrin, 27%27X with rhodium porphyrin\, 307~109 uilh ruthenium. t YO u ith ruthenium pot-phyrlw, 77&27X Carbon. C--C and C-N hond l’ot-mation. 20X Cwhon dioxide 111cle~lrocarboxytation. 2X6 I-educlion. 25X Carbon monoxide hydrogenation, t I.5 organoiron porphyrin inwr(ion, 3X reduclion. 25X rhodium porphyrin ncti\alion. 303-30.5 wuraled hydrocarbon ma(rices. I3 Carbon rerrachloride. in lel-roccnc alkytalion, lx~ts7 (‘arhoq Iation. in I’-donw ligand wtx~itution. 53 Carhq I f,-oup” cschange helwcen maill>, I2 I - I22 iwcyanldc dlrplacemenl. hl Ke-tlgatcd carhonyl. I22 wry-mixed metal. wc Very mixed-mcrat cxhonyt cluster\ Carhonylmetalacc anion\. 102 Carhonyl WI tide, 6 I C’alntysi\

325

INDEX

u ith nichel. I t-1 2 RCM, 207

D I>ecolllpo\iIion

(c,,-Cl~loroalkyltchlol-o\ilanes. I-IX (o-Chloroathyt )\ilanc\. 165-t 69, 177-t 7X Chlorohewenc. I63- I6S Chlorr~form. in t’errocrnr alkylation. 156-1.57 Chloromethylidync tigand. 73 ‘)-((Chlorohilyl)~tkyt)fluorene~. I76 I-Chlororoturne. 2OY Chloro/irconiuI11 comptcxeh. 237P238 Chromium porphyrin,. 242-213 Cobalt. ol-fanomrtalllc chcmi\try, 230-23 I Cobalt porphyrin\ alhene and alkyne reuctmns, 79 l-293 in alhene polymeri&on, 2X9%29 I hydride complrwx 2X7-289 ushonded alhyl and aryl complexc\ <‘(r-C bond energies, 7X3-235 fealurrs, 2X7-28.3 trcdox chemis(ry and rlectt-ochemi~try. 2X5-286

methyt(triphenylmethyl)dlchloro~ilane. 17i I-\ilaallcnc\, I X-I 9 Dehydratwn, methylcycloheualir, I I6 Diatoalhanea. 262 Ihroc~ter\. 27&277 Di-t-hulylhilylenc. 25-20 n’-Dlcar-bolidr anions, /irconium c~)mplexc\, ‘3X (Dichtoroalkyl)chloro\il~~~~~~ hcnxnr alhylation. I70 in hiphenyl alkytation. I72 (Dichlwoathyl )silnnes. I69- I73 (co.r,~~Dichloroalhyl)\ilnne\. IhY Dichlorohcnrene\. I70 Dichtorocarhcnc iron porphyl-in\. 215 ( I ,2-l)ichloroerhyl)\ilane, 176 ( I .?-l>ichlorocthyl)Irichloro~it;,n~~. I7 IPI 72 D&c>. very niixed~melal cluster wb\titution. so I>i~:thyldialtylmalonate. in nucleophilic carbcnc lC\h. 1% Dwthyl ruthenium porphyrin complex. 27 I 360-26 I Dih:docarhcne con~ple~e~. Dihydrogcn complrxe~, OS and Ru porphyrins, 27X-270 ~.S-l>ihydroilnida/ol-2-ylid~n~~. IYS Dimcri/ation heteroallrnc, 7 phenylacetylenc. 72 phenytrinylidenc. 72 Dimcthylhen/er,e. per-athytarion, t63Pt 65 Dimolybdenum~dl~ohal( cluhter. S-1 rhd~~~I~lt’ti~~c0111pkxc5. 90-9 I Dial dehytlraue. 300 Diphcnylacerylene. 7.1 Diphenyl diwttidc. 62-63 (I)iphenylmc~hyl)~ilane. 176 3.3.Diph~nylpropyn-3-01, 204 cl whitals. rr;tnilion metal porphyrin\. 2’8-229

326

INDEX

E

iron aryl pot-phqriw. 255 Iron porphyt-in\, 210 orgmocohalt porphyrins. 2X.5-2X6 o-alkyl rhodium porphyrins, 208 wry mixecl-metal cluster\. I?- I30 Electromc ahwrption. organoiron porphyl-iw 24%21Y Electronic ei’l’ccts nuclrophilic cwhene\. 18SPl 86 rhodium porphyrin dimcl-\ and hydrides, 2YY-300 Electronic structure. cohnlt porphyrin\. 2Y3 Electron transfer. metal exchange reaction\. X6 Electrophiles, very mixed-metal eluder ndditm~~. 61-67 Electroreduction it-on porphyrins. 217 Irhodium porphyrins. 2YS Energy Co-c‘ in Co porphyrin band\. 2X3-285 nuclrophilic carhene reorganwation, I X&l XY Ethoxy group. clcavqr, 73-74 Ethylalulnination. alkyncs. 210 Ethylben~cnc. 161-162 Ethyl dia~oacetnte, l’w OS carhene complex. 176-277 E~hynylniethylsilanc. I2 Extended Hiichel moIectIIu~- orbital calculation cuhane eluder\. I31 very mixed-metal clu\ters. 132-l 33

F Frnbke-Hall molecular orbital calculations. Ferrocene, alhylation. 155-l 58 Flash photolyhis, I -silaalleneh. 1% I4 Flash vacuum pyrolysis

I33

tr~~nethylailylvit~ylmcthylchloroh. I2 \ inyl\ilanc. 12-11 I~lu~~roalhynylailanr~. 17-l 8 I*luoronryl iwn octaethyltetraphenylporphyrins. 25.5 Fluorobewene alkylation. I70 nlrt;llloporphyrin interaction, 3 I3 Flt~orophq I iron porphyrin\. 2JY-30 Formaldehyde. condensation with Si. IS FricdalLC’rdi~ alkylntion wilh ~~llyl~hltrro\il~~~~r\ ;womatic hydrocarhon~. I SOL IS5 lcrr(wc’ne. ISS-IS8

G

frmnewwk linenrily. 36 synthesis and reactions. 22-Z tellurium complex. 3Y--10 I ~Germa-.~-pho~phaallenc. syntheai\, 30-i I Group 3 organomctallic complcxc\, 723-225 Group 3 porphyrins, 23 l-232 Group J olganometallic complexw, 23 Group 1 porphyrins, 23 l-232 Group 5 porphyrins. 21OL2-11 Group 6.group X-group 9 cluster\, 51-5-1 Group h+roup Y clusters, 52-53, fd-67. 72 Group &group IO clubter5. IO4

327

INDEX

Group 6 porphyrins. 240~241 Group 7 porphyrins. 240-24 I Group IO porphyrins. 3 I O-3 I2 Group I I porphyrins. 3 IO-3 12 Group 12 porphyrins. 3 I O-3 I2 Group I3 carhene analogs, 25-26 Group I4 heteroallene~ bonding models. 2-l crystal Wuctures. 3440 htwc wearch. -1344 I -germaallenes. 22-25 heteroketenimines. 25-30 hctcl-opho\phaallene\, 30&3 I NMR. 30-13 I-silnallenr\, 17-22 I-silaallene transition metal complex. I .2.3~tri5tannaallene. 32

OS and Ru porphyrins, 27X-279 rhodium(lll) porphyrin. 29X-302 Hydride migration. in Re-Pt clusters, I20- I2 I Hydrocarbon matrice\, CO-wturated. I4 Hydrodewlfuriation catalysts. 109. I I7 Hydrogenation. CO. I IS

1

32-33

H Hafnium porphyrins. 237-240 Halobenzenes. IS I Halocarbenc iron porphyrin\. 26 I Halogen\. very mixed-metal cluster wbstitution. 62-63 HDS catalysts. .YW HydrodesulfuriLation cata1y\t\ Heptane~metalloporphyrin interaction. 3 I3 Heteroallewa dimcriration, 7 group I3 bonding models, 24 crystal structures. 34-W future research. 43-44 I -germaallenes, 22-25 heterophosphaallene\. 30-3 I NMR. 4033 I-~ilaallenes, 17-22 I-\ilaallene transition metal complex. 32-33 I ,2.3-tristannaallene. 32 Heteroketenimines, 25-30 Heterometallic clu\ter\, I IS Heteropho\phaallenes. 30&3 I Hexanc. tn ferrocene alkylation, IS-l.57 i-Hexyne. 73 Homolysis. organoiron porphyrin Fe-C bond, 255-256 Hydride complexes cohnlt porphyrin\, 2X7-289

Imidazolium salts. I82 Imidazol-2~ylidene\ analog synthesis. 199-201 in &fin met:lthcsis. I9 I-l 92 preparation, I95 variou\ complexes, I X2 lodoaylbenome. 262 Iridium pal-phyrins n-bonded organo complcxea. 295%29X synthesis and mechanism. 29x-295 Iron. organometallic chemistry, 230-73 I Iron alkyl anion\. 25X Iron porphyrins carkne complexca. 259-263 oxidation catalysis. 263-264 \tlyl and stannyl complcxc\. 259 \yntheaia. 244-245 laocyanates, to group I4 cat-hene analogy. 25-26 Isocyanide~ carhonyl ligand displacement. 6 I lability, 28-29 rhodium porphyrin activation. 303-305 with cilylene, 27-2X

K Ketones, rhodium porphyrin reactiona. 306 Kinetic\, Fe-C bond homolysi\, 2% Kumada reactions, 21 l-215

L Lanthanides porphyrins. 23 l-232 Late transition metal porphyrins with nickel, 3 I O-3 I I with palladium. 3 I I with zinc. 3 I3 Ligand addition. wry mixed-metal clusters. 64-67 Ligand Ruxionality. very mixed-metal cluwr~. 116~124

328

INDEX

Ligand suhrtitution.

very mixed-meted carbonyl

cIusters other ligand\, SW33 P-donor lipnds, 49-58 Ligand t~an~formationr, wry cluax!, C-donor ligands, V-76 peral. 67-W other ligantls. 7679 Lithnrtion. cobalt porphyrin\. Lutetium porphyrin\. 235

mixed-metal

2X0-2X I

M Magnetic behavior. vwy mixed-metal clu\tcrs, 13lbl.12 Manganese porphyrin\. 233 Mesitylene. peralkylation. 164 Mesityl group. to alkynylpoly~ilane. I2 Metal carhonyl anion\. metal exchange reaction\, X0-90 Metal carbonyl hydride\. metal exchange reactions, X9-W Metal clusters Huxionality studies, I I7 phouphine rcactmn\. IO3 Metal exchange intcrmolecula ligated exchange, I23 in vcrg mlxed-metal cluster\. 6 I. 7%90 Mctallacarhoranc cluster\. expamion. I04 Metalloporphyrin oxo specie\. in oxidation chemiwy. 226 Metalloporphyrins organic molecule interactions. 3 12-3 I3 systematic chcmi\try. 224 Metals carhonyl exchange. I2 I-I 72 li-nmework rearrangcmcnt. 122-l 23 Methylcyclohexane. dehydration. I 16 Methylenc chloride. in Itrroccne alkylation, 156-157 Methyl(tl-iphcnyltnethyl)dichloro\ilan~. 175 Middle tranition element porphyrinr with chromium. molyhdenum, and tungsten. 242-243 developments. 240-241 with manganese. 243 with tantalum. 23 l-242 bligration alkynr group. I2 I

Ee-to-N. 111organoiron porphyrins, 254-255 hydride. W C Hydride migration 111organocohalt porphyrins. 286 Mlxed-metal clwtws, Huxionality studie\. I I7 MO calculation\. .,re Molecular orbital c;IIculations Model\ carbenc fence\. 19% ICII cytochrome P4SO. 262 voup I-1 heteroallene bonding, 21 Ecry mlxed-metal cluster catulyai\. I Oh-IOC) Molecular ol-bital calculationr, very mixed-met: cluster\. l?2-13.5 Molybdenum complexe\ elcctrochcmical behavior. I27 metal exchange reaction\. I K-104 Molyhdenuln~palladium catalysts. I I6 Molybdenum porphyl-ins. 232-247 Monoalkylhen/cne\ ;Ilkylntlon. IS2 l~(~lcalhylation. 161-163 Mononuclear metal complexes, core expansion. 01l-0 I

N Nickel calaly\ts with \ilacyclobutenes. I I-12 in thermoly\is. 9-10 Nickel complexe\, metal exchange reactions, 10s IO4 Nickel porphyrin%, 3 I O-3 I I Nitric oxide, into organoiron porphyrin\. 2% Nitrilcr. very mixed-metal cluster substitution. 59 Nttrtrgen, C-N hond formation. 208 Nilro\yl ligmd\. in Ku and O\ porphyrin complexes. 26X-339 Nuclear magnetic resonance cobalt pwphyrin\, 2X2-283 wwp I-l hrteroallcnes, 3Ob-13 cc lront III) o-alkyl and -aryl porphyrins. 24X pal-phyrin complexes. 229-230 I-hodlum porphyl-ins, 303-304 Nuclcophllic carhews bond di~tancea. I X7- I XX bond formations. 208 calorimetric stutl~e\. 183-l XS car;~lytic aclivity. 197&19X ccntroid bond distance. IX%I90

329

INDEX

fence ITKxiels, I90- I9 I oletin metathesis. l9lL207 treorganilation energies. I XX-I X9 stability, I X3 atereoelectronic properties. 185~1 X6 Qructural studies. 183~184 thermochemistry, 183-l X4 vilriou\ complexes I X2

0 Octaethq Icorrole, 250 Octaethyltetraphenylporphyrin, 250 Octanuclear anionic clusters. I30 Octanuclear clusters, I I2 OEC. .ACCOctaethylcorrole OE:TPP. WP Octaethyltetraphenylporphyrjn Oleiin metathesis. nucleophilic carhenes, lOlL207 Organic compounds metalloporphyrin interactions. 3 12-3 I3 rhodium porphyrin reactions, 306C307 Organocohalt porphyrins, 2X5-286 Organoiron porphyrins Fc-C bond hornolysis. 255-256 Fe-to-N migration. 254-255 small molecule insertion, 256-258 cynthesia and properties, 246-254 Organolithium reagents, 17-1X Organometallic complexes group 3 and 4 metalc. 224-225 in modern chemistry. 226 Organomctallic porphyrins. 225 Organoowiium porphyrins. 269-27 I Organoruthcnium porphyrins. 269-27 I Organosilicon compounds. I67 Organosulfur compounds. IOX Ortholnetallntion. PPhj. 7X Osmium porphyrins alkenr and alkyne complcxe~, 273-271 U,ith alkylidenes, 262 carhenr complexes, 275-278 dihydrogen complexes. 27X-279 hydride complexes, 27X-279 rr-bonded alkyl and aryl complexes. 266-273 synthc\i\, 264-26.5 Oxidation cntnly\is, by iron porphyrins. 263-264 or~anocohalt porphyrins, 2X6 O*\igCV

for cobalt porphyrins, 288 into organoiron porphyrins,

2.56~257

P Palladium-containin:! metal cluatcra. phosphine reactions, I03 Palladium nuclrophilic carhenes, 1X2 Palladium porphyrin?. 3 I I P-donor ligandc. very mixed-metal substitution. 49-5x Peralkylation. dimethyl- and trimethylhenrencs. 163~165 Petroleum reformation. I OX- IO9 Phcnylacetylene, 72 Phenylboronic acid. 209 Phenyl group migration. 254-255 Phenylvinylidene, 72 Phosphines with Pd.containing metal cluhterh. I03 P-H activation. 76 Pt&hound phosphine. I22 with Pt-containing metal cluster\., I03 very mixed-metal substitution, 49%5X Pho\phinidene clusters, P-donor ligand wb\titution, 53 Phoaphites. Lery mixed-metal substitution. 49-5x Photochemistry. iron porphyrin halocarhene complexes. 26 I Photolysi\ tran5ient lL\ilaallenes, S-13 triangular clusters, 9 I 4.Picoline with 0~ carbene complex, 276 with titanium porphyrin complexca. 236-237 Platinum-hound pho\phine. I22 Platinum-containin: metal clusters, I03 Platinum-rhenium clusters, 9X%lOO Polyalkylation bcnzcnc. 159-161 bcnrene derivatives. IS4 ~nonoalkylben~ene. 161-l 63 Polychloroben~enea, 171-172 Polymeriration, alkcrw. 2X9-291 Porphyrin complexes alkyliron(lII) complexes. 256-257 wth chromium, molybdenum, and tungsten, 242-243 with cobalt

330 alkene and alkyne reactions. 29 I-293 in alkene polymeri/.ation. 2X9-29 I hydride complexes. 2X7-289 rr-bonded alkyl and aryl complexes Co-C bond energica. 283-W feature\ .i 782-2X3 Ircdox chemistry and electrochemistry, 2X5-286 aynthe\ib and reactivity. 280-2X2 hynthehis. 279-280 coordmatmn chemistry, 227 diethyl ruthenium complex, 271 with hafnium. 237-240 with iridium u-bonded organo complexes. 295-298 synthcsix and mechanism, 293-29.5 wjith iron carhene complexe5. 259-263 oxldallon catalyslr.‘, 361 264 silyl and stannyl complexes, 259 synthchis. 244-24.5 with lutetium, 235 with manganese. 243 tnetalloporphyrin complexe\, 223 with middle transition elements, 240-24 I with nickel. ilOL31 I NMR
INDEX

organic aubWate reactions, 306-307 n-bonded organo complexes, 29.5-29X \ynthesi\ and mechanivll. 293-295 with ruthenium alkene and alkyne complrxe\, 271-274 carhcne complexes, 27-1-278 tllhydrogcn complexe\. 27X-279 hydride complexe\. 27X-279 rr-bonded alkyl and aryl complcxe\. 266.-273 \ynthe\i\. 263+76S with scandium, 732-23.5 u ith tantalum, 24 l-242 with titimlum. 235-217 with yttrium, 235 with lint, 3 I2 with /.trconium. 237-240 Porphyrins. a\ supporting lipands. 22X-23 I I ,2-Propadicne. .SW Allenc Propadienc\. atomic chqcs. 4 Propanal, for cobalt porphyrins, 2XX Protonation. very mixed-metal clu\tcrh. 64-60 Pyridines with ovnium carhene%, 276 rhodium porphyrin reactions. 306 with titanium porphyrins. 236-237 Pyroly\ia. transient I-silaallene5. S-13

R RCM. W C Ring closmg metathcsi:, Rectangular cluster, core transformation, IO0 Redox chemistry or~unocohalt porphyrin?. 2X5-286 Ku aryl and alkyl porphyrin complexes, 271-273 Reorgani/-ation energy. nucleophilic carheneb, 18%IX’, Rhenium, ligated carbonyl. I22 Rhcniun+platinum cIustcr\. YX~IOO, 108-109. 120-121 Rhodium nucleophilic cnrbene\. IX2 Rhodium(ll) porphyrin dimer. 2YX-302 Rhodium(ll1) porphyrin hydride. 2YX%302 Rhodium porphyrins carbene complexes. 307-300 C-H activation. 302Z303 CO and isocyanide activation. 303-30.5 dimer and hydride reactions, 29X-302 heterohimetallic complexes. 309-3 IO

331

INDEX

organic wbstrate reactions. 306-307 n-bvndcd organ0 complexes, 295-298 hynthcsis and mechanism, 293-295 Ring closing metathesis. 207 Kuthenium allenylidene complexes. 201-206 Kuthenlum curbeneh. 191-192 Ruthenium-indenylideneimidalol-2.ylidellc complexes, 202-204 Ruthenium porphyrins alkene and alkyne complcxe~ 273-271 alkylidene. 262 al-hew complcxea. 274-278 dihydropen complexes. 278-779 hydride complexes, 27X-279 n-bonded alkyl and aryl complexes, 266-273 synthcG5, 264-765 Kuthemun-I +ilaallene complex. 32-34. 3X-39

s Scandium pot-phyrins, 232-235 Selenido-contuining clu\ters, XX rr-bonded complexes alkcne and alkyne porphyrin complexca. 773-271 cobalt porphyrin\ Co-C bond energie\. 2X3-285 feature\ ..- 7X7-2X3 redox chemistry and electrochemistry, 2X5-286 \yntheGs and reactivity. 2X0-282 iridium porphyrins, 295-298 osmium porphyrin\, 266-273 porphyrin carbenc complexes. 274-278 rhodium porphyrina, 295-298 ruthenium porphyrins, 266-273 Silaallene~. 37 I -Sila;dlene\ bond lengths. 38 decompoition. IX-1 9 l’ramwork linearity. 31 NMK \tudy. 4 I, 4.3 I-CaCtioll, I9 ruthenium complex. 3X-39 \ynthe\ih, 17-l 8, 2 I tranwnt. S-13 tranGtion metal complex. 32-34 Silacqclohutane\, IX-19 Silacyclobutcnc\, I I-12 Silac~clopropenes. 9

I -Silacyclopropenes, 7 Silaketenes, 4. 37 I-Silaketcnea. 11-15 Silaketenimines. 37-38 I -Sila-3-phosphaalletlc, 3I Silapropadienes. I3 Silica-supported catalyst. I 13-l IS Silicon. condensation with formaldchydz, IS Silicon atom, in ferrocene alhylation. 157-l 58 Silicon compounds, Fried&Crafts alkylationa. l16-IS0 Silyl complcxe~. iron porphyl-in\, 259 Silylene with isocyanidcs, 27-28 prccurwr photolysi5. I3 Silyl cnol ether\, cobalt porphyrin reactions. 293 Silylmethyl complex. u ith /irconium. 339-210 I -Silylpropyl cation, I48 Sodium borohydride. for cobalt porphyrins. 2X8 Sl)ectr(~electrochcmic~~l studies. iron porphyrins. 249 Spectl-oscopy. Iron arq I porphyrin\. 255 Spiked triangular cluster\ metal rxchangc reactions. X9-90 precursor\, I02 I-Stannahrteninline. 26-27 Stannyl iron porphyrins, 259 Stereoelectrollics. nucleophilic carhene\, IX%IX6 Slyrenr, cqcloprop~l~~~~fion. 277-278 Suh
T Tantalum porphyrins, 231-232 Telluritun-I -germaallene complex, 3930 Temperature-prol!rammed reduction. I IS Tctra-capped clusters. I27- I29 I .2.3,4-Tetl-achlorobenane. I7 l-l.72 Tetrahedral heterometallic clusters. I IS Tetranuclear cluster\, XX-X9 Thermal stability. nuclcophilic carbenes. 20 I-202

332

INDEX

Thcrnlochrmi\tt-y. nuclrophilic cam-bcnc\, 1X3-1X1 Thcl-molyG\ trnn\irnt I -silaallene~. S-1 3 very mixecl-metal clustcr~. 101 -IO? Thiophenol. reactions. IOX Titanium porphyrins, 235-237 Toluene alkylation. lS1-152 mctalloporphyrin intwxtion. 3 12-3 I3 in tran~alkylation. 176 TPK. WC Tempcl-ature-programmed reduction Tlnnsnlkylatio~~\ h~wene, I SO (diphcnylmethyl )~ilanc. I76 Trams hcnding. Glahctcnc, 37 Tr3llaformation~. we Core trnn~forma~io~~s: Llfand tran\fot-ln;~tio~~\ Transition mc~;tl carhonyl\. I 12-l I3 Transition mctd complexc~ eal-ly tranhitmn mt‘d porphoryina, 23 l-230 late trawltion metal porphoryinr. 3 IO-3 I2 middle transition Clement porphyrin\. 210-113

apihetl. metal exchange lreilctmnb. XY-90 I .2.3-Trichlorob~nrcne. I7 I - I72 (Trichlorolnethyl)\ilan~s, 173-17X Trihalomethyl cobalt porphyrins, 2X I-2X2 Trimetallic clusters. I27 Trimethylbcwentx If% I65 TrimcthylchloroGlane, I2 Trimcthyl~ilyl~inylmethylchloro~ilanc. I2 Trimethylcinyl\il:tne. I2 Trinucltxr clu\ters. 8 I. 86 Trlph~nylpho\phinc. 7X Trisalhynq I--/irconium complexes, 23%240 I .2.?-Tri\tant~aallene. 32 Tungsten complexes, metal exchange reaction\, 10s IO3 Tung~tcn~platinum catalyze. I I3 Tungsten porphyrin\. 232-243 Tun:r~trn~rhodium complexes, IO1 ‘~LIIlg\ten-triit-idiutn cluster. 5.5-56

x X-m) atructurc cvoup I4 haxoallene\. nucleophilic carhcnea. ruthenium allcnylidrne 203-7-M Xylcw. 16% I64

Yttrium

porphyrins.

3440 IY-IY7. IO%20 complexes,

235

z Zinc porphyrin\. 3 12 Zirconium alkynyl complex. 23X--23 Zirconium porphyl-in dicarboxyla~e~. 240 Zit-conium porphyrins. 237-210

Cumulative List of Contributors for Volumes 1-36 Chatt. J., 12, I Chini. P.. 14, 285 Chisholm. M. t-1.. 26, 97; 27, 31 I Chiuwli. G. P.. 17, I95 Chojinowaki, J.. 30, 243 Churchill. M. R.. 5, 93 Coates, G. E.. ‘), IYS Coilman, J. P., 7, 53 Compton, N. A., 31, Y I Connrlly, N. c;.. 23, I : 24, X7 Connolly. J. W.. 19, I23 Corey, J. Y., 13, I30 Corritl, R. J. P., 20, 365 Courtney. A.. 16, 2-11 Coutt\, R. S. P., 9, 13.5 Covillc. N. J.. 36, 9.5 Coyle. T. D.. 10, 237 Crahtree. R. H.. 28, 2Y9 Craig. P. J., I I, .I? I (‘wh, K.. 28, xs Cullen, W. R.. 4, I15 Cundy. c. s.. II, 253 Curtis. M. D.. 19. 2 I3 Durtzndxxq. D. J.. 21, 113: 22, I30 Darendxxu-g. M. Y.. 27, I Davis. S. G., 30, I Deacon. G. B.. 25, 237 de Bow, E.. 2, I IS Deeming. A. J.. 26, I Dwy, R. E., 4,167 Dickwn. R. S.. 12, 323 Dixneuf, P. H.. 29, I63 Eisch. J. J.. 16, 67 Ellir, J. E.. 31, I Enwron. G. F.. 1, I Epstein. P. s., IY, 213 Erhcr, G., 24, I r?n\t. (‘. K., IO, 79 Errmgton. R. J., 31, Y I Evan\. J.. 16, 3lY Evans. W. J.. 24, I31 Fallrr. J. W.. 16, 21 I Farrugla. L. J.. 31, 301

Ahrl. E. W., 5, I: 8, II7 Aguilti. A.. 5, 321 Akkcrman. 0. S.. 32, 117 Alhuno. V. G.. 14, 285 Alp. H.. 19, IX3 ,Ander\on, G. K.. 20, 39: 35, I Angelici. R. J., 27, 51 At-xii. A. A., 30, I X9 Armitapc. D. A.. 5, I Armor-, J. N.. 19, I Ash. C. E., 27, I A\he. A. J.. III. 30, 77 Atuell. W. H.. 4, I Bainrs. K. M.. 25, I Barone, R., 26, I65 13a\\ncr, s. L.. 28, I Behwn\. II., IX, I Bennett. M. A.. 4, 353 Bickelhaupt, F.. 32, I37 Birmingham. J., 2, 365 Blinha, T. A.. 23, I93 Bockman, T. M.. 33, 5 I Bogd:movil:, B.. 17, I OS Bottomley. F., 28, 33’) Bradley. J. s.. 22, I Lirew. S. A.. 35, I35 Brinchnun, F. E., 20, 3 I3 Brook. A. ti.. 7,95: 25, I Bowo~-. J. R.. 36, 57 Brown. Il. C., 11, I Brown. T. L., 3, 365 Bruce. M. I.. 6, 273, IO, 273: II, 447; 12, 379: 22, so Brunncr. H., 18, IS I Buhl-o. W. E.. 27, 3 I I By”-\. P. K.. 34, I Cain. M.. 8. 2 I I Cal&~-on. N.. 17, 4JY (‘allahan. K. P., 14, I15 Cay. A. J.. 34. I Cartledge, F. K.. 4, I Chalk. A. J.. 6, I I’) (‘hanon. M.. 26, I65 333

334

Cumulative

FaUlk\, s. .I., 25,237 Fehlncr. T. l?. 21,57; 30, I89 Fc\senden. J. S., 18, 275 Fcssenden. R. J.. 18, 275 Fischer. E. 0.. 14, I Ford. P. C.. 28, I3Y Fornik J.. 28, 2 I Y For\ter, II.. 17, 255 Fraw. t? J.. 12, 323 FI-icdrich. t1.. 36. 2X Frwlrich. H. H.. 33, 2.i.i Friv. H. P.. I, 73’) Fiirwwx. A.. 28, X5 I~uruha\v~~, J.. 12, X3 Fuso~~, R. C.. 1. 22 I Gallop, M. A.. 25, I? I Garrou. I? E.. 23, 0s Griper. W. E.. 23. I: 24. X7 Geoft’roy. G. I,.. 18, 207: 24, 24’): 28, I Glma~x H.. I, 80: 4, I: 7, I GladfIrer, W. L., IX, 207: 24. II Gladqw. J. A.. 20, I Gliiwcr. B. I., 28, X5 Green. M. L. l-1.. 2, 35 Grq. R. S., 33, I25 Griflilh. W. P.. 7, 2 I I Gl-ownk~i. E., Jr.. 16, 167 Gubitr, s. t?. IO, 317 Guerin, C.. 20, 765 Gyding, H.. 9, 361 Haiduc, I., IS, I Ii Halaaa. A. F.. IX. 55 Halniltw. D. G.. 28, ?YY Handwake~-. H.. 36, 22’) Hand. J. F.. 6, I IY Har1. W. P.. 21, I Hxtley. F. H.. 15, IX9 Hawrhor~~c, M. F.. 14, I45 Heck. R. F.. 4, 243 tleimbxh I?. 8 3 2Y Hetme~-. B. J., 23, lY3 Henry. P. M.. 13, 363 Heppert, J. .A.. 26, Y7 Hcrherich, G. E.. 2.5, I YY Herrmann. W. A.. 20, I SC) Hicbcr. W., 8, 1 Hill, A. F., 36, Ii I Hill, E. A.. 16, I3 I Half, C.. 19, II!.? Hoft’mcister, Ii.. 32, 227

List of Contributors

for Volumes

l-36

Hol/lneier. P., 34, 67 Honeyman, R. T.. 34, I Hw\vII/. c’. I? 23, 2 I Y Hoamwe, N. S.. 30, YY Houccrotl. C. H.. 21, 57: 33, I Hwg. Y. Z., 20, I IS Hu$r\, R. P. 31, I X3 Ibw\. J. ii.. 14, 33 I\hlha\\>i. M., I’), .5 I IUCI, s. L).. 14, .ii Join. I-.. 27, I I .? Jain. V. K.. 27, I Ii .lanm. B K.. 17, ; I Y Jwiah. c‘.. 33. 20 I Jadrdxhi. J. T. B. I(.. 35, 241 Jwch. J 32, I71 Jolt>. P. W.. 8, 2Y: 19, 257 .)oKI\. K.. 19, Y7 Jww\. M. II.. 27, 27V Jonc\. I? R.. 15, 273 Jortl;l~~, Ii. F.. 32, 335 Juhc\. A E.. 12, 2lS Jul/i. P.. 26, 2 I7 Kac~. II. r>.. 3, I Katch. I’. 32. 111: 34, ?IY Kamin\hy. W.. IX, YY Kal/. 1‘. J.. 16, 7X3 Ka\r:rhata. N.. 12, X3 Kcniliii(t, K. II. W.. 27, 279 Kcttlc. S. EA.. IO, IYY Kilwr. M., IO, I IS Kilx H. P.. 27, S I Kill;. K. R.. 2. IS7 K~ng.\tw H. M.. I I, 253 Kisch. H.. 34, 67 Kitchillg. W.. 4, 267 Koch~. J. K 33, S I Ktider, R.. 2, 257 Krcikr. c. G.. 26. 2Y7 Kriipel-. G.. 24, I Kudaroshi. R A.. 22, l2Y Kilhteill. K.. 7, 211 Kui\ il:~. H. G.. 1, 17 Kutnad:~, M.. 6, I Y: 19, 5 I Lapper(, M. I:.. 5, 225: 9, 307: 11, 2.52 14. i-15 Lawrcncc, J. P., 17, UY Le Ho/cc. H.. 29, I63 Ledor. P. W.. 14, 349 Lillforct. I,.. 32, I

Cumulative

List of Contributors

Longoni, G., 14, 285 Luijten, .I. G. A., 3, 397 Lukehal-t, C. M., 25, 35 Lupin. M. S.. 8, 2 I I McGlinchey, M. J., 34, 285 McKillop. A., 11, I47 McNnlly, J. P., 30, I Macomber. D. W.. 21, I : 25, 3 I7 Maddox. M. L.. 3, I Maguirr. J. A.. 30, 99 M;titli\, P M., 4, 95 Mann. B. E.. 12, 135; 28,397 Mnnucl. T. A., 3, IX I Mxkics, P. R.. 32, I47 Mason, R., 5, 93 Master\, C.. 17, 01 Matsutnura. Y.. 14, I X7 May. A., 32, 227 Meister. G., 35,-l I Minpw, D. M. P.. 15, I Mochel. V. D.. IS,55 Moedrit7er. K.. 6, I7 I Molloy. K. C.. 33, 171 Monteil. F., 34, 2 IO Morgan. G. L., 9, 195 Morrison, J. A., 35, 21 I Mot .I. R., 33, 735 Mrowca. J. J.. 7, IS7 Miiller. G.. 24, I Mynott. K., 19, 257 Nngy, P. L. I.. 2, 325 Nakwmura. A., 14, 24.5 Newqanov. A. N.. 10, I Nwmann. W. P., 7, 241 Norman. N. C.. 31, 9 I Ol’\tcad. E. A., 17,449 Ohst. H., 25, I99 Okawxa. R., 5, 137: 14, IX7 Olivel-. J. P.. 8, 167: 15, 235: 16, I I I Owk. T., 3, 263 Oosthuizen. H. E., 22, 209 Ot\nka. S.. 14, 24.5 Pain. G. N.. 25, 237 Par\hnll. G. W.. 7, IS7 Paul. I.. 10, 199 Pew. Y.. 32, I2 I Petrohyan, W. S., 14, 63 Pettit. R.. I, I k/, G. P.. 19, I I’oland. .I. s., 9, 397

for Volumes

l-36

Poliakoft’, M.. 25, 277 Popa, v.. 15, I I3 Pourreau, D. B.. 24, 249 Powell. P., 26, I25 Pratt. J. M.. 11, 331 Prokai. B.. 5, 225 Pruett, R. L.. 17, I Rae. G. S.. 27. I I3 Rauhenheimer, H. G.. 32, I Rauwh. M. D.. 21, I: 25.317 Reet~ 3 M. 7: 3,16 3.3 Reutov, 0. A., 14, 63 Rijkens. F.. 3, 397 Ritter, J. J.. 10, 237 Rochow. E. (2.. 9, I Rokioki. A., 28, I39 Roper. W. R.. 7,53: 25, I2 I Roundhill, D. M.. 13, 273 Rube/hov, A. Z., IO, 347 Salerno. G.. 17, 195 Salter. I. I).. 29. 249 Sat&J.. 21, 231 Schade. C.. 27. I69 Scha\ericn. c‘. J.. 36, 283 Schmitlbaul-. H., 9, 259: 14, 205 Schraurer. G. N., 2, I Schubert. IJ.. 30, IS I Schulw. D. N.. 18, SS Schumann. H., 33. 291 Schwebke. G. L., 1, X9 Seppelt. K.. 34, 207 Set/w. W. N.. 24. 3.53 Seyl’erth, D.. 14,97 Shapakin. S. Yu., 34, 149 Shen, Y. C., 20, I IS Shriver, D. F.. 23, 219 Siebert. W., 18,301: 35, IX7 Sikora. D. J.. 25. 3 I7 Silverthorn. W E.. 13, 47 .Singleton. E.. 22, 209 Sinn , H.. 18 3 99 Skinner, H. A.. 2,49 Slocum, D. W., 10, 79 Smallridge. A. J.. 30, I Smeet\, W. J. J.. .32 3 147 Smith. J. D.. 13,153 Speier, J. L., 17,407 Spck, A. L., 32, 137 Staflbrd. S. L.. 3, I Staricryk. W.. 30, 233

335

336

Cumulative

Stone. F. G. A., I, 113: 31,53: 35, 13.5 su, A. c. L.. 17,x’) Sudick. K. M.. 25, 73 S&\-Fink. G.. 35, -I I Sutin, L.. 28. i3Y Swincer. A. G.. 22, SC) Tamao. K.. 6, I Y Tale. D. P.. IS, 55 Taylor. E. (‘.. II, l-17 Templeton. J. I... 29, I Thayer. J. S.. 5, I hY; 13, I ; 20, 3 13 TheodoGtru. I.. 26, 165 Tirnms, P. I... 15, S3 T’odd. I.. J.. 8, X7 ~ouchard. D., 29, I63 l-~-awn. V. F.. 34. IlY Trrichel. I? M.. I, 113: 11,71 Twji. J.. 17. l-11 Twtwi. M.. 9, 36 I ; 16, 74 I Turncy. T. W.. 15, 53 ryfield, S. P.. 8, I I7 Ushn. R., 28, 2 I Y Vahrenkamp. H., 22, IhY ian der Kerk, G. J. M., 3, 307

List of Contributors

for Volumes

1-36

\,:,n Kwn. G.. 21, I.5 I; 35, 211 Veith. M.. 31, 26’) wey. P. N.. 15, I XY wn RquC Schleyer, P.. 24, 351; 27, 16 Vriwc. K.. 21, IS I Wad;1. RI.. 5, I37 Walton. D. R. M.. 13, 453 Wailr\. I’. c‘.. 9, I 35 Webster. D. E.... IS, I37 Welt/. E.. 25, 277 We\t. R., 5, 169: 16, I: 23, lY3 Wcl-ner. H.. 19, I.55 White. I).. 36, YS Wihq. N.. 23, I3 I : 24, I70 Wilt\. D. R.. 1 I, 207 Wilhc. G.. X, 2Y Willlnni~. R. t:.. 36, I Winter, M. J.. 29, IO I Wo,jcichi. A., II, X7: 12, i I Y;lnlanloto. /\., 34, I I I Ya\hina, N. S., 14, 63 Zirgler. K.. 6, I Zuckwrnan. J. J.. 9. 2 I Zyhill. C.. 36, 22Y

Cumulative Index for Volumes 37-46 VOL..

PAGE

10 3-l 3’)

I I75 71

39

I

46

233

338

Hampden-Smith. Hanusa, Timothy Hard. John F.. Hauhrich. Scott.

Cumulative Index for Volumes 37-46

Mnrh J.. .we W$c/ak. William A. P.. .wc Hay\. Melanie L. .wc Gauvin. Franqoi\ Power, Philip. and Twmley, I3rcndan. Illewrrrr

f)cr,wri~v\

O/

S~~.~I~~~~~)P cord Honc/i,,y in Mouo~nrc~lcc~r M~~fr,lloc~cwc~., _. _, _. _. _. _. Hemmc. Ina. .$w Klingehicl. Uue Hopkins. Michael D.. .xv Manna. Joseph Humphrey, Ma!-k G.. .,L’<’Whi~tall. Ian R. Humphrey, Mark G., ,wc Waterman. Swan M. Ihmels. Heiktr, .wc Bel~ner. Johannes .__,._..,...___....___..,, ,_,... ._...__...,, ,.,,_._ Jafarpour. Lalch. and Nolan, Steven P.. 7i-~r,f.tiriorf-Mcrcil .S\~\/e,n.\ Hwr-rug (I Nw

/“““d\ Kawachi, ALashi. w Tamao. Kohei Klingchicl. Clwe. and Hemmc. Ina. /rr~i/~o.\i/tr,~c,.ccd Kclotcd Cuu~/wwd\.- Svr/w.\/\ mrtl KPol’florl.\ Klingehtel. Uwe. .sw Bode. Katritl Klosin. July. w Jonrs. William M. Lot/, Simon. Van Rooyen. Petru\ H., and Meyer, RIU. 0, rr-Rr-i~/~sirq Li,qclut/r iis Ri,lrc~rtr//i~ o,rd 7~iwtci//ic CO,ll/h\C.\ Lucax Nigcl T.. .we Waterman. Suun M. Manna, Joseph, John. Kc\ in I>.. and Hophin\. Michael. I).. T/w Ho/rt/iyq of’Me/o/A/X\,IY/ Crm/dewr ,._,,..,,.,. ._..__.....__.....__.........__.....__.._._............_.. Manner\, Ian, Kir~,y-O/wrriu,~ tP)I~r,~c,~i~c~rio~~ o/ Mrtr~l/r~~~c~tro~~~/~~~~~~~~: A NW, Korctc~ fo Tro,~\irirui Mctoi-Bmrtl /+‘r,/wwr.\ Mathur. Pradccp. C‘hr~/~,o~:r,~-Hrit/~c,t/ Mcrr~/~C‘c/,-hofi~/ (‘~ur~/~/e\-cv McDonaph, Andrew M.. .rer Whitlall. Ian R. Meyet-, Rib, wc LOU, Simon Moss;. John R.. wc r\nderux Jo-Ann M. Newcomh, Martin xv’ <‘hatg~lialoglu. Chryswaomo Nwuher. Hubert. w Aumann. Rudolf Nolan, Stow P.. .,cc Jai’arpou~-, Laleh Opine. Hirorhi, and Tohiu. Hiromi, RCt/,qd Silderw trd C;cru~defw (‘ow /I/? rc.\ Ohwnhi. Renji, and Wc\t. Robert. C’/~e~uisf~;~rfSrtrh/r /Xvi/cwc\ _. _. Pcplow, Mark A., .sw Gibson. Susan E. Power. Philip P.. .wc BI-other-5. Penelope J. Power, Philip. wc Hautxich, Scott Ranalconjalovo. Henrl, .\vc Escutlie. Jean Piilm. Mclamc. .\cc Xlche. Reinhold

43

I

40

117

339

Cumulative Index for Volumes 37-46

13 43

197 125

3x

155

37 3x 43

I IX’) X7

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