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 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=~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
--
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. 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.‘= (‘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. 0.: Mah. ‘I‘. C. W.; (‘ban, K. S. l,/rq. C‘/r/,i,. A