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22 Organometallic chemistry of bi- and poly-nuclearcomplexes

By S. DOHERTYDepartment of Chemistry, Bedson Building, University of Newcastle-upon-Tyne,

Newcastle-upon-Tyne, NE1 7RU, UK

1 Introduction

This review covers developments in the organometallic chemistry of bi- and poly-nuclear complexes published in 1997. A number of issues of Dalton Trans. containPerspectives either dedicated to polynuclear organometallic chemistry or that incor-porate some aspect of this field and include: back-to-back articles1a,b that address themechanism of low-energy fluxional processes in [Fe

3(CO)

12~nLn], the second of which

re-emphasises fluxionality by libration of the Fe3

triangle within the ligand icosahed-ron, a further article that discusses the dynamics and fluxionality of small metalcarbonyl clusters1c and an extensive review of the organometallic chemistry of earlytransition-metal carbenoid complexes.1d Other relevant review articles include: selec-tive transformations of alkynes with ruthenium catalysts1e and the structure, solutiondynamics and reactivity of the new titanium imido compounds [Ti(NR)Cl

2(py)

3].1f

2 Titanium, zirconium and hafnium

The reaction between [TiF3Cp*] or [TiF

3CpA] and CaF

2gave [MTiF

3Cp*

4NCaF

2]

and [(TiF3CpA)

4CaF

2] respectively, which contain an eight-co-ordinate Ca2` located

in a crown-ether like core.2 The hexacarbonyltitanate(2[ ) [Ti(CO)6]2~ reacts with

[AuCl(PR3)] to give [Ti(CO)

6(AuPR

3)]~, which contains a seven-co-ordinate geo-

metry about Ti and which may be regarded as a structural model for the presentlyunknown [TiH(CO)

6]~.3 Reduction of [TiF

2Cp

2] with potassium affords the binuc-

lear g5 : g5-fulvalene complex [MTi(k-F)CpN2(k-g5 : g5-C

10H

8)], based on a symmetrical

Ti2F2butterfly skeleton folded along the Ti—Ti direction.4 Methyl carbanion abstrac-

tion from [TiMe3Cp*] with the potent Lewis acid [B(C

6F5)3] affords [TiMe

2Cp*(k-

Me)B(C6F5)3] which reacts with a further equivalent of [TiMe

3Cp*] to afford the

unusual methyl-bridged dimer [MTiMe2Cp*N

2(k-Me)][B(C

6F5)3Me].5 The tweezer

complexes [Ti(g1-C———CSiMe3)2Cp*

2][Mg(thf)Cl] and [Ti(g1-C———CR)

2Cp*

2]

[Mg(OEt)Cl] (R\Me, Et, Pr/, Bu/, cyclohexyl, Ph or SiMe3) catalyse the head-to-tail

dimerisation of terminal acetylenes, RC———CH, to 2,4-disubstituted but-1-en-3-ynes.6The structure of a compound previously assigned as [MTi(k-SiH

2)Cp

2N2] was shown to

be the titanocene() silyl-bridged dimer [MTi(k-H-SiH2)Cp

2N2].7 Mixtures of

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[TiCl2MeCp], thiol and base have been used to prepare new Ti—S containing aggre-

gates. For instance, thermolysis of a [TiCl2MeCp]—benzyl mercaptan—lithium hy-

droxide mixture at 80 °C gave [Ti(k3-S)

4(k

3-O)

4Cp

6] based on a pseudo-octahedral

array of TiCp fragments.8Reduction of [TiCl

2(g5-C

5Me

4SiMe

3)2] by Mg resulted in activation of a C—H

bond of one of the trimethylsilyl substituents to give the paramagnetic mixed-metalcompound [MTi[g5-C

5Me

4(SiMe

3)][g5-C

5Me

4SiMe

2(k-CH

2)](k-H)

2Mg(thf)N

2]

whereas reduction in the presence of Me3SiC———CSiMe

3gave [Ti(g5 : g1-

C5Me

4SiMe

2CH

2)(g5-C

5Me

4SiMe

3)] rather than the expected g2-alkyne complex

[Ti(g2-alkyne)Mg5-C5Me

4(SiMe

3)N

2].9 The alkenyl zirconocenes [ZrX(MeC——

CH2)Cp

2] (X\Cl or Br) react with the dialkyl zirconocene [ZrMe

2Cp

2] (R\Me, Et

or Bu/) to give the alkynyl-bridged complex [(ZrCp2)2(k-X)(k-C———CCH

3)] via a path-

way involving exchange of Bu and Br groups and b-elimination from a mononuclearp-vinyl complex.10

Alkylation, thermolysis or reduction of various thiolate derivatives of monocy-clopentadienyl titanium phenoxide complexes induces C—H activation or C—S bondcleavage. For example, thiolation of [TiClMe(OC

6H

3Pr*

2-2,6)Cp] with 1,1-

dimethylethanethiol, in the presence of base, gave [TiMe(OC6H

3Pr*

2-2,6)(SCMe

3)Cp]

while its ethyl substituted counterpart [TiMe(OC6H

3Pr*

2-2,6)(SCH

2CH

3)Cp] is un-

stable and liberates methane to give the binuclear derivative [MTi(OC6H

3Pr*

2-

2,6)Cp(k-SCHMe)N2]. Thermal elimination of (PhCH

2)2S from [Ti(OC

6H

3Pr*

2-

2,6)(SCH2Ph)

2Cp] gave the dimer [MTi(OC

6H

3Pr*

2-2,6)(k-S)CpN

2].11 Trityl tetraf-

luoroborate abstraction of a propynyl group from [Zr(g1-C———CMe)2Cp

2] 1 gave the

cation 2 [Zr(g1-C———CMe)Cp2]` which reacts with a further equivalent of [Zr(g1-

C———CMe)2Cp

2] to afford [(ZrCp

2)2(k-C———CMe)(k-MeC———C—C———CMe)]` 3, bridged by a

hexadiyne ligand that contains a planar four-co-ordinate carbon (Scheme 1). A dy-namic process involving p—n exchange of the bridging hexadiyne ligand was

ZrC

C

CC

Me

ZrC

C

Cp2ZrC

ZrCp2

C

Me

CCC

CMe

Me+

+

3

21

[CPh3][BPh4]

Me Me

Scheme 1

identified.12 Hydrogenation of the dicarbollide complex [(HfMeCp*)2(C

2B9H

11)]

gave the hydride-bridged complex [HfCp*(g5-C2B9H

11)(k-g5 : g1C

2B9H

11)-

HfCp*(H)]; the latter catalyses the hydrogenation of internal alkynes to cis-alkenes,via a mechanism thought to involve rapid insertion into a Hf—H bond of a mononuc-lear complex followed by rapid hydrogenolysis of the resulting Hf—C bond.13 Additionof carbazole to [Ti(CH

2SiMe

3)4] affords the sparingly soluble alkylidene-bridged

dimer [MTi(cb)2(k-CHSiMe

3)N

2] which reacts with 2,6-dimethylphenylisocyanide

(xyNC) to give [Ti2(cb)

3(k-xyNCCSiMe

3)MxyNCH——C(SiMe

3)C——NxyN]; the bridging

amidoalkyne and iminoacyl ligands result from coupling of an alkylidene bridge withone or two equivalents of xyNC respectively.14 Elimination of methane from the

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zirconium diene complex [ZrMe(C4H

4Me

2-2,3)Mg5-C

5H

3(SiMe

3)2-1,3N] gave the k-

g1 : g4-butadienyl bridged complex [MZr(k-g1: g4-C4H

3Me

2-2,3)[g5-C

5H

3(SiMe

3)2-

1,3]N].15

3 Vanadium, niobium and tantalum

The methyl groups Me! and Me" in the binuclear ansa bridged g5-cyclopentadienylim-ide derivative [NbMeMk-C

5H

4(CH

2)2NNMk-NCH(CH

2)2C

5H

4NNbMe!Me"] ex-

change slowly at 233K. In the proposed mechanism of exchange the stereochemicallynon-rigid niobium site undergoes a geometrical isomerisation induced by dissociationof the strained alkylideneamide ligand from the niobium atom bearing Me! and Me".The two methyl groups then exchange co-ordination positions by rotation under theansa bridge.16 The half-sandwich hydrazide(2[ ) niobium complex[MNbCl

2(NNMe

2)CpN

2] is dimeric with one hydrazide ligand bonded in a linear

monodentate manner while the second bridges both niobium atoms in a k-g1 : g2-manner. The substitution reactions of the two chloride bridges in[NbCl

2(NNMe

2)Cp] by a variety of lithium, sodium and magnesium reagents has

been explored.17 The attempted dimethylation of [VCl2MN(C

6H

3Pr*

2-2,6)NCp] results

in reductive dimerisation and formation of the k-methyl complexes [MV[N(C6H

3Pr*

2-

2,6)]Cp(k-Me)N2(k-Mg)] and [MV[k-N(C

6H

3Pr*

2-2,6)]CpN

2(k-Me)]. The formation of

these compounds was discussed in relation to the deactivation of a-olefin polymerisa-tion precatalysts.18 Reaction of N,N-diphenylformamidinate or N,N-di(tolyl)for-mamidinate with [Ta

2Cl

6(SMe

2)3] in the presence of a reducing agent gave binuclear

tantalum complexes containing NR, CNR or HCNR via C—N bond cleavage. Notably,reaction in the absence of reducing agent also results in C—N bond cleavage indicatingthat the formamidinate ligand oxidatively adds to the TaIII—TaIII bond.19 Reductivedimerisation of [VX

3(g5-C

5Me

4R)] (X\ Cl or Br; R\Me or Et) or cyclopentadienyl

transfer from [SnBu3(C

5Me

4R)] to [VX

3L3] (L \ thf or tht) gave [MV(k-Br)

2(g5-

C5Me

4R)N

2] and [MV(k-Cl)

2(g5-C

5Me

4R)N

3], both of which contain a four-legged

piano stool arrangement of ligands about the V centre. The former compound behavesas a paramagnet in the solid state while the susceptibility of the latter is moreconsistent with antiferromagnetic behaviour.20 Bottomley and co-workers used asimilar strategy to prepare [MV(k-Cl)

2Cp*N

3], which reacts with O

2and NaN

3to give

[VCl2(O)Cp*] and [MVCl(k-N)Cp*N

2].21 The triply-bridged NbII complex [Li(tmen)]

[Nb2Cl

5(tmen)

2] reacts with Li[N(3,5-Me

2C

6H

3)Ad] to give the tetravalent diamag-

netic dimer [MNbMN(3,5-Me2C

6H

3)AdN(3,5-Me

2C

6H

3)(k-NAd)N

2] involving a rare

amido C—N bond cleavage. In contrast, reaction with Li[NCy2] gave the nitrido-

bridged mixed-valence dimer [Li(tmen)][MNb(NCy)2N2(k-N)Mk

3-NLi(tmen)N], poss-

ibly via an N2

activation pathway.22 Reduction of [TaCl(S)(SCPh3)Cp*] gave the

triangular cluster [Ta3(S)

3(k

3-S

3BH)Cp*

3] which contains a TaIV, TaIV, TaV d2-

core.23

4 Chromium, molybdenum and tungsten

Trimethylamine N-oxide-promoted air oxidation of [Mo2(CO)

4(k-RC———CR@)Cp

2] af-

fords the organometallic oxo complexes [Mo2(O)

2(k-O)(k-RC———CR@)Cp

2]

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(R\ CO2Me or Ph; R@\H or Ph). In the absence of air, oxidation does not take

place, although in the presence of P(OMe)3

or Bu5NC, trimethylamine N-oxidepromotes monosubstitution of [Mo

2(CO)

4(k-RC———CR@)Cp

2] to give [Mo

2(CO)

3L(k-

RC———CR@)Cp2]. The addition of [NO][BF

4] to solutions of [Mo

2(CO)

4(k-

RC———CR@)Cp2], under conditions of air oxidation gave the nitrosyl complexes

[Mo2(CO)

3(NO)(k-RC———CR@)Cp

2][BF

4].24 The cyclotriphosphorus complex

[M(CO)2(g3-P

3)Cp] reacts with [M@

2(CO)

4Cp

2] (M \M@\ Mo or W) to afford

[MonW

2~n(CO)

4(k-g2-P

2)Cp

2] 4 and [Mo

nW

3~n(CO)

6(k

3-P)Cp

3] 5; the latter can be

oxidised by atmospheric oxygen to give [MonW

3~n(CO)

6(k

3-P——O)Cp

3] 6, which

contains a k3-P——O capping ligand,25 and by elemental sulfur to give

[MonW

3~n(CO)

6(k

3-P——S)Cp

3].26 Activation of the P

2bridge in [M

2(CO)

4(k-g2-

P2)Cp

2] (M\Mo or W) with M@OH (M@\Na or K) followed by addition of HBF

4gave high yields of [M

2(k-H)(CO)

4(k-PH

2)Cp

2].27

[O]

654

(CO)2CpMo WCp(CO)2

P P (CO)2CpMo WCp(CO)2

P

WCp(CO)2

(CO)2CpMo WCp(CO)2

P

WCp(CO)2

O

The reactivity of trans-[Mo2(CO)(CN)(k-SR)

2Cp

2]~ is largely dependent on the

nature of R. Complexes where R\Me, Pr* (syn/anti isomers) or Ph (anti isomer) areS-methylated whereas for R \Ph (syn isomer) and CF

3(syn/anti isomers) N-methyl-

ation is dominant. Substitution of electron-releasing by electron-withdrawing groupsat the bridging thiolate stabilises the HOMO and increases the gap between thisorbital and the electrophile’s LUMO which should favour charge control of thereaction, i.e. N-methylation.28 A range of fluorinated k-arylimido dimolybdenumcomplexes have been prepared to examine the extent to which steric and electroniceffects influence the structure of the [Mo

2(k-NR)

2] core. The arylimido complexes

[Mo2(O)

2(k-NR)(k-O)Cp@

2] and [MMo(O)(k-NR)Cp@

2N2] (R\C

6H

4F-2 or

C6H

4CF

3-2) have been prepared from [MMo(CO)

3Cp@

2N2] and the corresponding

nitrobenzene. In contrast, the bis(imido) complexes [MMo(O)(k-NC6H

3F2-2,6)Cp@

2N2]

were the only products of the reaction between O2NC

6H

3F2-2,6 and

[MMo(CO)3Cp@

2N2].29 Time-resolved IR spectroscopy showed that photolysis of

[MCr(CO)2Cp*N

2] affords the triply-bridged CO loss intermediate [Cr

2(k-CO)

3Cp*

2].

The reaction of this complex with CO is considerably faster than that of its ironcounterpart [Fe

2(k-CO)

3Cp

2].30

The dinuclear d3—d3 diolate complex [Mo2(NMe

2)2L2] [H

2L\ 2,2@-methyl-

enebis(6-tert-butyl-4-methylphenol)] exists as bridged and chelated isomers. Althoughthese do not interconvert even at 110 °C, addition of pyridine or MeCN results inbridge—chelate isomerisation [*H8 \[ 19(^ 1) kcalmol~1, *S8 \[ 25(^ 3) calmol~1K~1.]. In contrast, [W

2(NMe

2)6] reacts with H

2L to give [W

2(k-H)(k-

NMe2)(g2-L)(g3-L)(NMe

2)(HNMe

2)] via a reversible oxidative addition.31 Thermoly-

sis of this product under a dynamic vacuum results in elimination of HNMe2

to give[W

2(NMe

2)2(g2-L)

2] which, in the presence of neutral donor ligands, undergoes

oxidative addition of a C—H bond to the W2

centre.32 Substitution of the bridgingchloride in [Mo

2(k-Cl)(k-SMe)

3Cp

2] with HS(CH

2)nSH (n\ 2 or 3) affords the

dithiolate-bridged dimer [Mo2Mk-S(CH

2)nSHN(k-SMe)

3Cp

2]. However, while substi-

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tution of chloride for PPhH2

gave [Mo2(k-PPhH)(k-SMe)

3Cp

2], PPh

2H substitutes

the thiolate bridge trans to the chloride to give [Mo2(k-Cl)(k-PPh

2)(k-SMe)

2Cp

2].33

Potassium 1,2,4-triisopropylcyclopentadienide reacts with [Mo(CO)6] to give the

sterically hindered dimer [MMo(CO)3(g5-C

5H

2Pr*

3-1,2,4N

2].34

Decarbonylation of [Mo2(CO)

4(k-tedip)Cp

2] 7 results in oxidative addition of a

P—O bond of the bridging ligand to give the mixed phosphido—phosphonate[Mo

2(CO)

2Mk-P(OEt)

2NMk-OP(OEt)

2NCp

2] 8, which reacts rapidly and reversibly

with carbon monoxide to give [Mo2(CO)

4Mk-P(OEt)

2NMk-OP(OEt)

2NCp

2] 9 (Scheme

2). In contrast, photochemical decarbonylation of [Mo2(CO)

4(k-tedip)Cp

2] was less

987

(CO)2CpMo MoCp(CO)2

P(OEt)2(EtO)2PO P(OEt)2O

(CO)CpMoP

MoCp(CO)

P(OEt)2O

(CO)2CpMoP

MoCp(CO)2

(OEt)2 (OEt)2

–CO –CO

Scheme 2

selective and gave a mixture of [Mo2(CO)

2Mk-P(OEt)

2NMk-OP(OEt)

2NCp

2],

[Mo2(CO)

2Mk-P(OEt)

2NMk-OP(OEt)

2NCp

2] and the triply-bonded dimer [Mo

2(k-

CO)(k-tedip)Cp2], while photolysis of its tungsten counterpart gave the hy-

drido—cyclopentadienylidene complex [W2(k-H)(CO)

3(k-tedip)(k-g1: g5-C

5H

4)Cp]

together with [W2(CO)

4(k-tedip)Cp

2].35 Thermal decarbonylation of the dppm-

bridged complex [W2(CO)

4(k-dppm)Cp

2] gave the triply-bonded complex

[W2(CO)

2(k-dppm)Cp

2] 10 together with low yields of the P—CH

2bond cleavage

product [W2(CO)(O)(k-PPh

2)(k-CH

2PPh

2)Cp

2] 11. Photolytic decarbonylation also

gave the triply-bonded dimer via the hydrido—cyclopentadienylidene intermediate[W

2(k-H)(CO)

3(k-dppm)(k-g1: g5-C

5H

4)Cp] 12.36 Similarly, upon photolysis the

(CO)2W W(CO)Cp

PPh2Ph2P

H2C

HCpW WCp

PPh2Ph2PC

OC

CO

10 1211

PPh2H2C

(CO)CpWPPh2

WO

Cp

H2

mixed-metal complex [MoW(CO)4(k-dppm)Cp

2] loses carbon monoxide to afford the

C—H activated intermediate [MoW(k-H)(CO)3(k-dppm)(k-g1: g5-C

5H

4)Cp], which

readily loses another CO to give the corresponding triply-bonded dimer.37 Notably, incontrast to its tungsten counterpart, thermal decarbonylation of [Mo

2(CO)

4(k-

dppm)Cp2] gave high yields of the mixed phosphido—phosphinomethanide dimer

[Mo2(CO)(k-PPh

2)(k-CH

2PPh

2)Cp

2].38

Addition of weak nucleophiles to the dicarbenium complex [Mo2(CO)

4(k-g3: g3-

CH2C———CCH

2)fv][BF

4] occurs exclusively at the carbenium centre to generate

[Mo2(CO)

4(k-g2 : g3-CH

2C———CCH

2R)fv][BF

4] (R \OH, C

6H

4OMe or C

6H

4OH).

Subsequent reaction with NaBH4

gave the functionalised alkyne complexes[Mo

2(CO)

4(k-g2 : g2-CH

3C———CCH

2R)fv] (R\C

6H

4OMe or C

6H

4OH).39 The elec-

trochemical reduction of the carbenium cation [Mo2(CO)

4(k-g2 : g3-HC———CCR1R2)]`

has been investigated by cyclic voltammetry, controlled potential electrolysis and

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coulometry. The substituents R1 and R2 control the reduction process. Complexeswith R1\H, R2\H, Me or Et undergo an irreversible or quasi reversible one-electron reduction while those with R1\ H, R2\Fc; R1\Me, R2\Me or Phreduce in a single two-electron step. The nature of the final products, either a dimer ora k-alkyne/k-enyne bridged complex, is dependent on the nature of R1 and R2.40

Dimethylaminoethyl-substituted cyclopentadienyl ligands have been used to pre-pare the dinuclear k-sulfido molybdenum complex [MMo(k-S)(g5-C

5H

4CH

2CH

2NMe

2)N

2(k-S

2CH

2)] which readily protonates to give the water-sol-

uble dication [MMo(k-S)(g5-C5H

4CH

2CH

2NMe

2H)N

2(k-S

2CH

2)][NO

3]2.41 Substi-

tution of carbon monoxide in [W2(CO)

7(k-PPh

2)Cp

2] with a range of diphosphines

Ph2PXPPh

2(X\CH

2, C

2H

4or C

3H

7) gave [W

2(CO)

6(k-PPh

2)(Ph

2PCH

2PPh

2-

iP)Cp2], [W

2(CO)

5(k-PPh

2)(Ph

2PC

2H

4PPh

2-i2P,P@)Cp

2] and [MW

2(CO)

6(k-

PPh2)CpN

2(k-Ph

2PC

3H

6PPh

2-iP,iP)] in which the diphosphine is pendant, chelat-

ing and interbridging respectively.42Ab initio MO and density functional theory calculations show that the puckering of

the W2C

2ring in [MWL

2(k-CR)N

2] (L\H, Me, F or OH; R \H, F or Me) complexes

is largely a function of L. Electron-withdrawing n-donating ligands favour a planargeometry while p-donors prefer a puckered non-planar system. Structure—reactivityrelationships of these complexes have been discussed.43 Density functional calcula-tions have been carried out on the metathesis reaction between [W

2(OR)

6] and

alkynes. The pathways examined include reduction of the C———C bond either through aparallel interaction between the reactants to give a 1,2-ditungstacyclobutadiene or aperpendicular approach to yield a 1,3-ditungstacyclobutadiene via a tetrahedranestructure. The 1,3-ditungstacyclobutadiene intermediate was suggested to be the mostlikely, although the inclusion of relativistic effects was necessary to discriminatebetween these pathways.44

5 Manganese, technetium and rhenium

Reduction of a series of [Mn(CO)3(g5-thiophene)]` cations 13 under an atmosphere of

CO affords the dimanganese metallothiacycles [Mn2(CO)

7(k-g1 : g1 : g5-

SCRCHCHCR@)] 14 in which a Mn(CO)4

fragment has inserted into a C—S bond.Hydrogenolysis of 14 results in opening of the thiophene ring to give the thiolate-bridged dimers [Mn

2(k-H)(CO)

6(k-g2 : g2-SCRCHCHCHR@-S)] 15 (Scheme 3).45 Hy-

dodimetallation of diphenyldiazomethane with the unsaturated complex [Re2(k-

OCCO

CO

SMn(CO)4R

R′Mn

OCCO

CO(CO)3Mn Mn(CO)3

S R

H

H2+e–

13 14 15

S

Mn

R

R′

R′

Scheme 3

H)2(CO)

8] gave [Re

2(k-H)(CO)

8Mk-g1-NHN(CPh

2)N] whereas reaction with ethyl-

diazoacetate results in loss of N2

to give [Re2(k-H)(CO)

8(k-g2-CH

2CO

2Et)].46 The

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reaction between [Re2(CO)

8(NCMe)

2] and diazocyclopentadiene, in a 1: 2 molar

ratio, gave the diazo-bridged dimer [Re2(CO)

8Mk-N

2(C

5H

4)2N]. A possible mechanism

for its formation involves heterolysis of the Re—Re bond.47The homoleptic neopentoxide cluster [Re

3(k-OCH

2Bu5)

3(OCH

2Bu5)

6] reacts with

ethyne to give [Re3(OCH

2Bu5)

9(k-g2-HC———CH)] and with disubstituted alkynes

(RC———CR@) to liberate pivaldehyde (b-elimination) and give the alkenyl clusters [Re3(k-

OCH2Bu5)

3(OCH

2Bu5)

5(g1-CR——CHR@)].48 The rhenium alkoxide cluster [Re

3(k-

OPr*)3(OPr*)

6] reacts with ethylene and isobutylene to give [Re

3Et(k-OPr*)

3(OPr*)

5]

and [Re3(Bu*)(k-OPr*)

3(OPr*)

5] respectively. Both clusters reversibly b-eliminate

acetone to give [Re3(H)(R)(k-OPr*)

3(OPr*)

4] (R\Et or Bu*); thermodynamic

[*HL— \ 13.2 ( ^ 0.7) kcalmol~1, *SL \ 24.1 (^ 2.2) calmol~1K~1] and activation[*H8 \ 17.6 ( ^ 1.0) kcalmol~1, *S8 \[ 25.0 ( ^ 3.1) calmol~1K~1] parametershave been determined.49 The neopentoxide cluster reacts with ethylene, ethyne andinternal alkynes to give similar products.50 In the case of phenylacetylene, hydrometal-lation gave a mixture of p-vinyl complexes corresponding to Markovnikov andanti-Markovnikov addition. The acylate anion Li[Re

2(k-H)(k-PCy

2)MCPh(O)N(CO)

7]

eliminates PhCHO upon reaction with [XAu(PPh3)] (X \ Cl, Br or I) to give the

metallatetrahedrane [Re2(k-H)(CO)

7(k-PCy

2)MAu(PPh

3)N

2].51

Catalytic-ring opening macrocyclisation of 3,3-dimethylselenetane by[Re

2(CO)

9(SeCH

2CMe

2CH

2)] gave three new polyselenoether macrocycles via a

series of ring-opening additions similar to that recently established for thietane macro-cyclisation.52 The 3,3-dimethylthietane complex [Re

2(CO)

9(SCH

2CMe

2CH

2)] reacts

with excess 3,3-dimethylthietane at 100 °C to give low yields of 3,3,7,7,11,11-hexa-methyl-1,5,9-trithiacyclododecane, 3,3,7,7,11,11,15,15-octamethyl-1,5,9,13-tet-rathiacyclohexadecane and 3,3,7,7,11,11,15,15,19,19-decamethyl-1,5,9,13,17-pen-tathiacycloicosane. The catalytic activity is low compared to the analogous reaction ofthietane and 3-methylthietane and the bulk of the products are high molecular weightoligomers of 3,3-dimethylthietane. It appears that as the number of substituents in the3-position of the thietane increases macrocycle formation becomes progressively lessfavourable.53 The catalytic ring-opening of b-propiothiolactone by[Re

2(CO)

9(NCMe)] and [Mn

2(CO)

9(NCMe)] gave (SCH

2CH

2C——O)

npolymer as well

as a mixture of new macrocycles including 1,5,9,13-tetrathiacyclohexadecane-2,6,10,14-tetrone (SCH

2CH

2C——O)

4and 1,5,9,13,17,21-hexathiacyclotetracosane-

2,6,10,14,18,22-hexone (SCH2CH

2C——O)

6. Under similar conditions 3,3-dimethyl b-

propiothiolactone was converted into polymer only. The possibility of light-generatedmetal-based radicals was discussed.54

Two tetranuclear open chain clusters have been prepared. Reaction of [NEt4]

[Re2H(CO)

9] with the electronically unsaturated complex [Re

2(k-H)

2(CO)

8] gave

[Re4(k-H)

2(H)(CO)

17]~ while the lightly stabilised dimer [Re

2(CO)

9L] (L\ thf, H

2O

or NMe3) gave [Re

4(k-H)(CO)

18]~. The solid-state structures and NMR solution

behaviour of both compounds have been reported.55 Variable-temperature 13C and2-D EXSY experiments have been used to probe the fluxionality of the triangularcluster [Re

3(k-H)

3(k-g2-NC

5H

4)(CO)

10]~. The favoured mechanism of exchange ap-

peared to be rigid rotation of the apical [ReH2(CO)

4] moiety with respect to the

doubly-bridged basal dimetallic fragment.56The 32-electron dimer [MRe(CO)

2Cp*N

2] 16 reacts with alkynes to give the dimetal-

lacyclopentenones [Re2(CO)

4Mk-g1 : g2-CH——CR(O)NCp*

2] 17. In the case of propyne,

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low-temperature NMR studies showed that the kinetic product [Re2(CO)

4Mk-g1: g3-

CH3C——CHC(O)NCp*

2] readily isomerises to its thermodynamically more stable

isomer [Re2(CO)

4Mk-g1 : g3-CH——C(CH

3)C(O)NCp*

2]. Protonation of these metal-

lacyclopentenones results in ring-opening formation of cationic k-vinyl complexes 18(Scheme 4).57 High yields of the metal disulfido complex [MRe(k-S

2)Cl(g5-CpA)N

2] have

been isolated from the reaction of [ReCl4(g5-CpA)] and bis(trimethylsilyl)sulfide. The

disulfide ligand reacts with acetylene and ethene to afford ethenedithiolate andethanedithiolate complexes respectively.58 The k-CNxyl bridged structure of the

Re Re

CO

Cp*Cp*

CO

COCO

Re Re

CC

CO

R(H)(H)R

CO

Cp*Cp*

OCOC

RH Re ReC

CR

H

COCp*

Cp*

OCOC

HCOCF3CO2H

+

181716

Scheme 4

‘yellow’ isomer of the dirhenium salt [Re2Cl

3(CO)(CNxyl)

2(k-dppm)

2]Y (Y \Cl,

SO3CF

3, PF

6or ReO

4) was confirmed by an X-ray crystallographic study of its

one-electron reduced paramagnetic congener [Re2Cl

3(CO)(CNxyl)

2(k-dppm)

2].59

The unsaturated cluster salt [Re(CO)3(dmf)

3][Re

3H

4(CO)

9] undergoes a skeletal

transformation in chlorofrom—dmf solution to give [Re(CO)3(dmf)

3]2[Re

5H

7(CO)

15]

and [Re(CO)3(dmf)

3][Re

4H

5(CO)

12], the distribution of which depends upon the

concentration of dmf. The first of these products is a 74-electron square-based pyra-midal cluster with all hydrides edge bridging. In dichloromethane at low concentra-tions of dmf [Re(CO)

3(dmf)

3]2[Re

5H

7(CO)

15] transforms into [Re(CO)

3(dmf)

3]

[Re6H

7(CO)

18] while at moderate concentrations [Re(CO)

3(dmf)

3][Re

3H

4(CO)

9]

and [Re(CO)3(dmf)

3][Re

4H

5(CO)

12] are formed.60

6 Iron, ruthenium and osmium

Insertion of PhC———CH into cis-[Fe2(k-H)(CO)

4(k-CO)(k-PPh

2)(k-dppm)] affords cis-

[Fe2(CO)

4(k-PhC——CH

2)(k-PPh

2)(k-dppm)] and trans-[Fe

2(CO)

4(k-HC——CHPh)(k-

PPh2)(k-dppm)], which differ in the regioselectivity of alkyne insertion and the relative

orientation of the phosphido and diphosphine bridging ligands. In contrast, reactionof trans-[Fe

2(k-H)(CO)

4(k-CO)(k-PCy

2)(k-dppm)] appeared to give exclusively the

b-isomer [Fe2(CO)

4(k-HC——CHPh)(k-PCy

2)(k-dppm)], although thermolysis of the

reaction mixture gave the a,b-unsaturated acyl complex trans-[Fe2(CO)

4Mk-

O——CC(Ph)——CH2N(k-PCy

2)(k-dppm)] which was thought to form via CO insertion into

the unidentified b-substituted isomer.61 Addition of acids to the k-ethenyl complex[Fe

2(CO)

4(k-CH——CH

2)(k-PCy)

2(k-dppm)] results in loss of ethylene. When the anion

is co-ordinating subsequent attack at the diiron centre generates the halide- andcarboxylate-bridged diiron complexes [Fe

2(CO)

4(k-X)(k-PCy

2)(k-dppm)] and

[Fe2(CO)

4(k-O

2CR)(k-PCy

2)(k-dppm)] respectively. Protonation with acids of non-

co-ordinating anions results in the formation of [Fe2(CO)

6(k-PCy

2)(k-dppm)][Z]

(Z\ PF6

or BF4), the yield of which increases under a carbon monoxide atmosphere.

Detailed NMR studies showed the vinyl—hydride [Fe2(H)(CO)

4(k-CH——CH

2)(k-

PCy2)(k-dppm)][BF

4] to be an intermediate in these reactions.62 The synthesis and

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crystal structure of the diiron acetylide complexes [Fe2(CO)

4~n(Ph

2PC———CPh)

n(k-

C———CPh)(k-PPh2)(k-dppm)] (n \ 0 or 1) have been reported and compared with the

related complexes [Fe2(CO)

6~n(PPh

3)n(k-C———CPh)(k-PPh

2)] (n\ 0 or 1). There ap-

pears to be no significant change in the nature of the acetylide binding upon successivecarbonyl substitution, which suggests that other factors, namely electronic stabilisa-tion of the transition state, must influence the free energy of activation for p—n acetylidefluxionality.63

The allenyl complex [Fe2(CO)

6(k-PPh

2)Mk-g1 : g2ab-C(H)——C——CH

2N] 19 has been

synthesised and crystallographically characterised. Variable-temperature 1H and 13CNMR studies revealed a high energy exchange process that equilibrates the dias-tereotopic allenyl protons as well as two independent non-degenerate trigonal rota-tions that act to exchange the carbonyl ligands on each Fe(CO)

3unit.64 Or-

ganolithium reagents react with 19 via an unusual nucleophile—carbonyl—allenylcoupling to afford the b,c-unsaturated ketones [Fe

2(CO)

5MP(OMe)

3N(k-PPh

2)Mk-

g1 : g2-[R@C(O)CRH]C——CH2N] (R\ Me, Bun, Ph or thienyl). Alcohols react similarly

to afford the binuclear b,c-unsaturated esters [Fe2(CO)

5(k-PPh

2)Mk-g1 : g2-

[R@OC(O)CRH]C——CH2N] 20 (R——H or Ph), which contain a five-membered metalla-

cycle by virtue of co-ordination of the ester carbonyl. Trimethylphosphite substitutesthe metal-co-ordinated ester carbonyl to afford the ester-functionalised k-g1 : g2-al-kenyl complex [Fe

2(CO)

5MP(OMe)

3N(k-PPh

2)Mk-g1 : g2-[R@OC(O)CRH]C——CH

2N] 21

(R——H or Ph) (Scheme 5).65 Addition of trialkylphosphite, P(OR)3(R\Me or Et), to 19

(CO)3Fe Fe(CO)3

CCH

PPh2

CH

H

(CO)3Fe Fe

C C

PPh2

CH HH

H CO

OR′

COCO

Fe Fe(CO)3

CC

PPh2

HH CH2C(O)OR′

(MeO)3POC

OCP(OMe)3R′OH

212019

Scheme 5

gave the a,b-unsaturated phosphonate-bridged complex [Fe2(CO)

6(k-PPh

2)Mk-g1 : g2-

MeC——CH[P(O)(OR)2]N] 22, which was thought to result from an Arbuzov-type

dealkylation or direct nucleophilic attack of water at the phosphorus atom of azwitterionic phosphonium intermediate. In contrast, in the presence of PhC———CLi,P(OR)

3reacts with [Fe

2(CO)

6(k-PPh

2)Mk-g1 : g2ab-C(H)——C——CH

2N] via P—Ca bond for-

mation and 1,3-hydrogen migration to give [Fe2(CO)

6(k-PPh

2)Mk-MeC——

C[P(OR)3]N] 23.66 The binuclear allenyl complex [Ru

2(CO)

6(k-PPh

2)Mk-g1 : g2bc-

(CO)3Fe Fe(CO)3

CCMe

PPh2

(CO)3Fe Fe(CO)3

C CMe

PPh2

P(OR)3

H

P(OR)2

O

23

–

+

22

C(Ph)——C——CPh2N] reacts with dppm to afford [Ru

2(CO)

4(k-PPh

2)(k-dppm)Mk-g1: g2-

C(O)C(Ph)——C——CPh2N] containing an acylallenyl ligand, and [Ru

2(CO)

4(k-PPh

2)(k-

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dppm)Mk-g1: g2bc-C(Ph)——C——CPh2N] and with dppe to give [Ru

2(CO)

5(g1-dppe)Mg1-

C(Ph)——C——CPh2N], which contains a terminal g1-co-ordinated allenyl ligand.67

Low-temperature addition of aryllithium nucleophiles to hexacarbonylcyclooc-tatetraenediiron gave an acylate intermediate which, when treated with [Et

3O][BF

4],

gave the acylate and carbene derivatives [Fe2(CO)

6MC(O)RN(1-4-g: 5-7-g-C

8H

9)] and

[Fe2(CO)

6MC(OEt)RN(1-4-g: 5-8-g-C

8H

8)] respectively; the former probably results

from rearrangement of a hydroxycarbene intermediate.68 Stepwise treatment of anethereal solution of k-hexacarbonyl(divinylbenzene)diiron with aryllithium reagents,RLi, and [Et

3O][BF

4] affords the isomerised divinylbenzene co-ordinated alkoxycar-

bene [Fe2(CO)

6Mk-CH

2——CHC

6H

3CHCH

2[C(OEt)R]N]. Similarly, hexacarbonyl(p-

divinylbenzene)diiron reacted under the same conditions to afford the correspondingisomerised alkoxycarbene.69

Heterocyclic ligands prepared by the condensation of thiophene-2-carbaldehydeand N-methylpyrrole-2-carbaldehyde react with [Fe

2(CO)

9] to give [Fe

2(CO)

6Mk-g3-

(R)NCH2C——CC(H)——C(H)—XN] (R \ Fc, Ph or Cy; X\S or NMe) via activation of the

heterocycle b-C—H bond and 1,3-hydrogen migration to the imine carbon.70 Similarly,imines of thiophene-3-carbaldehyde or indole-3-carbaldehyde react with [Fe

2(CO)

9]

to afford the corresponding isomers [Fe2(CO)

6Mk-g3-(R)NCH

2C——C—X—C(R@)——C(RA)N]

(X\ S or NH).71 The thienyl Schiff base N-(2-thienylmethylidene)aniline reacts with[Fe

2(CO)

9] to give three products; a cyclometallated k- g1 : g2-thienyl-g1: g1(N)

methylidene aniline hexacarbonyldiiron complex 24, a hexacarbonyl complex contain-ing an organic fragment derived from the coupling of two thienyl imines and a

(CO)3Fe Fe(CO)3

N

H2CS

R

24

hydrogenation product of the original thienyl Schiff base.72 The binuclear complex[MFe(CO)

3N2L] where L\ 1,3,5,7-tetrabutyl-s-indacene, exhibits strong electron—elec-

tron coupling between the iron centres, as evidenced by a 810mV separation betweenthe first and second one-electron oxidation waves.73

The reaction of [Fe2(CO)

2(k-CO)(k-CSMe)Cp

2]` 25 with various carbon-based

nucleophiles has been examined. Addition of allylmagnesium chloride affords[Fe

2(CO)

2(k-CO)(k-CSMe)Mg4-C

5H

5(allyl)NCp] 26 and the alkylidene complex

[Fe2(CO)

2(k-CO)Mk-C(SMe)HNMg5-C

5H

4(allyl)NCp] 27 (Scheme 6). In contrast, or-

ganolithium cuprates [Li2Cu(CN)R

2] add to the bridging alkylidyne to give

[Fe2(CO)

2(k-CO)Mk-C(SMe)RNCp

2] and [Fe

2(CO)

2(k-CO)Mk-C(g2-Ph)PhNCp

2] or

the vinylidene-bridged derivative [Fe2(CO)

2(k-CO)(k-C——CH

2)Cp

2]. Reaction of

[Fe2(CO)

2(k-CO)(k-CSMe)Cp

2][CF

3SO

3] with PhC———CLi and thienyllithium gives

the novel alkylidene complexes [Fe2(CO)

2(k-CO)Mk-C(SMe)C(O)C———CPhNCp

2] and

[Fe2(CO)(k-CO)Mk-C(SMe)C(O)(2-C

4H

3S)NCp

2] 28 via carbyne—nucleophile—al-

kylidyne coupling. In the case of 2-thienyllithium carbon—carbon bond formationbetween the thienyl nucleophile and Cp ring also gave [Fe

2(CO)

2(k-CO)(k-SMe)Mg4-

C5H

5(2-C

4H

3S)NCp].74 Addition of 2-thienyllithium to the thiocarbyne complex cis-

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Fe FeC

S

CO

Cp

CO

Cp

OC

Me

Fe FeC

S

CO

CO

Cp

OC

Me

H

Fe FeC

SMe

CO

CO

Cp

OC

H

+

(allyl)MgCl

272625

Scheme 6

[Fe2(CO)

2(k-CS)(k-CSMe)Cp

2][CF

3SO

3] also results in C—C bond formation with a

co-ordinated Cp to give the neutral butadiene complex [Fe2(CO)

2(k-CS)(k-CSMe)(g5-

C5H

5)Mg4-C

5H

5(2-C

4H

3S)N] together with low yields of the acyl derivative

[Fe2(CO)MC(O)C

4H

3SN(k-CS)(k-CSMe)Cp

2]. In contrast, the aminocarbyne

[Fe2(CO)

2(k-CO)(k-CNRR1)Cp

2] (R\ R1\Me, R\ Me, R1\ CH

2Ph) reacts with

2-thienyllithium to give the acyl derivative [Fe2(CO)(k-CO)MC(O)C

4H

3SN(k-

CNRR1)Cp2] 29.75 For R DR@, C—C bond formation depends on the nature of the

carbanion. Organolithium reagents, LiR (R\Me, Bu/ or Ph), add to Cp to give[Fe

2(CO)

2(k-CO)Mk-CN(Me)RN(g4-C

5H

5R)Cp] as the sole reaction product, while

organolithium cuprates [Li2Cu(CN)R

2] and LiC———CR add to CO to give the stable

acyl derivatives [Fe2(CO)(k-CO)MC(O)RNMk-CN(Me)RNCp

2] and [Fe

2(CO)(k-

CO)MC(O)C———CRNMk-CN(Me)RNCp2] respectively.76 Addition of an excess of LiR to

the diiron k-ethynediyl complex [MFe(CO)2Cp*N

2(k-C———C)] gave the bridging al-

lenylidene complex [Fe2(CO)

2(k-CO)(k-C——C——CR1R2)Cp*

2] 30 (R1\R2\H). The

Fe Fe

CS

CO

CpCp

OC

COS

Fe FeC

CO

Cp

C

Cp

OCO S

2928

NR R

Me

same complexes have been prepared by the addition of nucleophiles to the diironk-acylvinylidene complex [Fe

2(CO)

2(k-CO)Mk-C——C(H)C(O)R1NCp*

2]. Protonation of

[Fe2(CO)

2(k-CO)(k-C——C——CR1R2)Cp*

2] 30 takes place at the b-carbon of the al-

lenylidene to give the cationic k-vinylcarbyne [Fe2(CO)

2(k-CO)Mk-

CC(H)CR1R2NCp*2]` 31 which reacts with nucleophiles at Cc to give the functional-

ised k-vinylidene complex [Fe2(CO)

2(k-CO)Mk-C——C(H)CR1R2NuNCp*

2] 32 (Scheme

7). Similar vinylidene complexes have also been prepared by addition of nucleophilesto Cc of [Fe

2(CO)

2(k-CO)(k-C——C——CR

2)Cp

2] followed by protonation at Cb.77

Fe FeC

CO

CO

Cp*

OC

Cp*Fe Fe

C

C

CO

CO

Cp*

OC

Cp*

CR1

R2H

Fe FeC

CO

CO

Cp*

OC

Cp*

30

H+ Nu–

32

+

31

H CNu

R2

R1

C

CR2R1

Scheme 7

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Oxidation of the electron-rich thiolate-bridged complex [Fe2(CO)

2(k-SEt)

2Cp*

2]

with 7,7,8,8-tetracyanoquinodimethane and tetracyanoethylene gave [Fe2(CO)

2(k-

SEt)2Cp*

2][tcnq]

2and [Fe

2(CO)

2(k-SEt)

2Cp*

2][tcne]

2respectively. The structures

of the compounds differ only in the nature of the planar polycyanohydrocarbon anion.There are no extended magnetic interactions in either salt as evidenced from variable-temperature magnetic measurements.78 The catalytic hydrogenation of [MFe(CO)(k-CO)N

2Mg5 : g5-(ind)SiMe

2Me

2Si(ind)N] gave the tetrahydroindenyl complex

[MFe(CO)(k-CO)N2Mg5 : g5-(H

4ind)SiMe

2Me

2Si(indH

4)N] as a mixture of separable cis

and trans isomers. Thermolysis of cis/trans-[MFe(CO)(k-CO)N2Mg5 :g5-(H

4ind)-

SiMe2Me

2Si(indH

4)N] gave trans/cis-[MFe(CO)

2(g5 : g1-H

4indSiMe

2)N

2], the cis(trans)

isomer giving exclusively the trans(cis) product via a pathway involving (i) pairwiseopening of the CO bridging ligands and (ii) subsequent homolysis of the Fe—Fe bondand rearrangement via a concerted or stepwise process.79 The synthesis, properties,reactivity and crystal structure of [MM(CO)(k-CO)(g5-C

5Me

4CF

3)N

2] (M\Fe or Ru)

have been compared with those of their parent iron and ruthenium counterparts. Bothcompounds crystallise as the trans isomer with bridging carbonyl ligands; the g5-C

5Me

4CF

3ligand is electronically equivalent to the C

5Me

5ligand.80 Addition of two

equivalents of LiNRH to the chloride-bridged dimer [MRuCl2(g6-C

6H

6)N

2] gave the

amido complex [RuCl(NHR)(g6-C6H

6)] while reaction with four equivalents of the

amide salt gave [MRu(NR)(g6-C6H

6)N

2], which exists as a monomer or dimer depend-

ing on the steric demands of the arene and amido ligands.81 Treatment of an aqueoussolution of [Ru(H

2O)

3(g6-C

6H

6)]2` with sodium tetrahydroborate affords the binuc-

lear cationic triply-bridged complex [Ru2H

3(g6-C

6H

6)2]` which reacts with addi-

tional NaBH4

to give [Ru2H

4(g6-C

6H

6)2] and [Ru

2H

3(BH

4)(g6-C

6H

6)2].82

The perfluorosulfanylvinyldiiron(0) complex [MFe(CO)3N2Mk-C(SMe)(CF

3)C(CF

2)N]

33 reacts with PPh3

to give a salt containing the [MFe(CO)3N2Mk-C(CF

3)C(CF

3)-

SMeN]~ anion 34, formally derived from fluoride-ion transfer, and the cation[Fe

2(CO)

5(PPh

3)Mk-C(CF

3)C(PPh

3)C(CF

3)SMeN]` 35. In contrast, reaction with

trimethyl phosphite affords the neutral dimer [MFe(CO)3N2Mk-C(F)C[P(O)(OMe)

2]

C(CF3)SMeN] 36, possibly via P—C bond formation 37, transfer of fluoride to the

phosphonium centre and elimination of methyl fluoride (Scheme 8).83Thermal rearrangement of the [MRu(CO)(k-CO)N

2(g5 : g5-C

5H

4SiMe

2Me

2SiC

5H

4)]

affords [MRu(CO)2(g5 : g1-C

5H

4SiMe

2)N

2] via metathesis of the Si—Si and Ru—Ru

bonds.84 Variable-temperature 13C and 31P NMR spectroscopic studies revealed that[Ru

2(CO)

6(k-PCy

2)2] exists as an equilibrium mixture of two isomers, one of which

has the same symmetrical conformation as that in the solid while the other results fromtranslocation of one cyclohexyl ring to an axial position.85 Cyclopentadienyl ligandeffects on enthalpies of protonation of [Ru

2(CO)

4(g5-Cp@)

2] have been examined. In all

cases protonation occurred at the Ru—Ru bond to form [Ru2(k-H)(CO)

4(g5-Cp@)

2]

[SO3CF

3] in which all of the carbonyls are terminal. The ordering of basicities was

rationalised by considering that the more strongly donating Cp@ ligands increase thebasicitiy of the Ru—Ru bond, and that dimers with bridging CO’s are substantially lessbasic than those with all terminal carbonyl ligands, for Cp@ ligands of similar donorcapacity.86 Two phases of the organometallic polymer [Ru

2(CO)

4Mk-g2-O

2PMe

2N]

nhave been structurally characterised by X-ray powder diffraction, one at 295K theother at 50K.87

Reaction of [Ru2(CO)

6(k-PPh

2)(k-g1 : g2ab-C———CC———CR)] (R\Bu5 or Ph) with

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FeFe

S

COOC CO

OCOC

OC

CC C F

FMe CF3

Fe

Fe

S

COOC CO

OCOCOC

C

C

MeCF3

CF3Fe

Fe

S

COOC CO

OCPh3P

OC

CC

Me CF3

CPPh3

CF3

Fe

Fe

S

COOC CO

OCOC

OC

CC

Me CF3

CP(OMe)3

F

F

Fe

Fe

S

COOC CO

OCOC

CO

CC

Me CF3

CP(OMe)2

F

O

–MeF

P(OMe)3

3637

+PPh3

+

35

–

3433

Scheme 8

[Pt(PPh3)2(g2-C

2H

4)] and [Ni(cod)

2] or [Ni(CO)

4] gave [Ru

2Pt(CO)

7(PPh

3)(k-

PPh2)(k-g1 : g1 : g1-C———CC———CR)] and [Ru

4Ni(CO)

12(k-PPh

2)(k

4-g1 : g1 : g4-

Bu5C———CC4C———CBu5)] which results from addition of a Pt fragment and Ni-mediated

C—C coupling reactions respectively.88Terminal acetylenes react with [ClCp*Ru(k-SPr*)

2Ru(H

2O)Cp*][OTf] to afford

the terminal vinylidene [ClCp*Ru(k-SPr*)2Ru(——C——CHR)Cp*]` 38. Hydrolysis of this

cation (R \CO2Me or COMe) gave [ClCp*Ru(k-SPr*)

2Ru(CO)Cp*]` 39 and

MeC(O)R while [ClCp*Ru(k-SPr*)2Ru(——C——CH

2)Cp*]` gave the k-acyl complex

[Cp*Ru(k-SPr*)2RuMk-C(O)MeNCp*]` 40. Both hydrolysis products appear to be the

result of nucleophilic attack of H2O at Ca of the vinylidene to give an acyl complex

(R\ H) or the k-b-ketoacetyl intermediate [Cp*Ru(k-SPr*)2(k-g1: g1-

COCH2COR@)RuCp*)]` 41 (R@\Me or OMe) which decarbonylates at the dimetal

centre via the enolate carbonyl complex [(CO)Cp*Ru(k-SPr*)2Ru(OCR@\CH

2)-

Cp*]` 42 to give [ClCp*Ru(k-SPr*)2Ru(CO)Cp*]` 39 (Scheme 9).89 The n-vinyl

carbene complex (1,3-g-1-methoxy-anti-2,3-bis(methoxycarbonyl)prop-2-ene-1-ylidene)tricarbonyliron 43 reacts with [Ru(CO)

3(cod)] to give the binuclear vinyl

carbene [FeRu(CO)6Mk-g1 : g2-C(OMe)C(CO

2Me)CH(CO

2Me)N] 44 in high yield.

Substitution with triphenylphosphine occurs selectively at the ruthenium centre andtrans to the M—M bond.90 Addition of diazoalkanes (N

2——CR1R2) to the labile methyl-

ene-bridged complex [Ru2(CO)(k-CO)(NCMe)(k-CH

2)Cp

2] results in C—C coupling

to give the bridging alkenyl complex [Ru2(k-H)(CO)

2(k-CH——CHR1)Cp

2] (R1\H) or

alkene CH2——CR1R2 (R1, R2D H) under extremely mild conditions. Labelling experi-

ments have been used to gain insight into the mechanism which was thought to involvemigratory insertion of a g1-alkylidene-k-alkylidene intermediate.91 The thermal reac-tion of [Ru

2(CO)

4(k-O

2CMe)(k-dppm)][BPh

4] with PPh

3, PPh

2Me or PEt

3affords

[Ru2(CO)

2(PR

3)2(k-O

2CMe)(k-dppm)(k-PPh

2)] and [Ph

2PCH

2PR

3][BPh

4] which

results from activation of the P—CH2

bond of dppm, and involves an intermediatewhich contains co-ordinated PPh

2and CH

2PPh

2fragments.92 Oxidative addition of

the H—Si and H—Sn bonds of hydrosilanes and hydostannanes to the bis(k-methylene)

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Cp*Ru RuCp*

PriS SPri

COO

R′

Cp*Ru RuCp*

PriS SPri

COMe

Cp*Ru RuCp*

PriS SPri

CO O

R′

Cp*Ru RuCp*

PriS SPri

COCl

Cp*Ru RuCp*CC

PriS SPri

H R

38

H2O

39

41

H2O

42

–R′C(O)Me

40

+++

++

Cl

Scheme 9

Fe

COMe

CC

CO2Me

H

CO2Me

COOCCO (CO)3Fe

Ru(CO)3C

C

C CO

OMeH

MeO2C

MeO

4443

complex [Ru2(CO)

2(NCMe)(k-CH

2)2Cp

2] gave the hydrido—k-methylene complex

[Ru2(H)(CO)(MR

3)(k-CH

2)2Cp

2] (M\Si or Sn). Intramolecular exchange between

the hydride and k-methylene hydrogens took four days to reach equilibrium. In thecase of dihydrosilane, phenylsilane and triphenylsilane one of the two methylenebridges eliminates as methane to give [Ru

2(SiR

3)(k-CH

2)(k-SiR

2)Cp

2].93

Dehydration of 1-phenylprop-2-yn-1-ol in the presence of [Fe3(CO)

12] gave the

allenylidene cluster [Fe3(CO)

9(k-CO)Mk-C——C——C(H)PhN] which reacted with methanol

‘stabiliser’ to afford the ferrole [Fe2(CO)

6MPh(H)CCCHC(OMe)ON].94Thermolysis of

[Ru3(CO)

12] in octane containing cycloocta-1,3-diene gave two structural isomers,

[Ru3H

2(CO)

9(C

8H

10)] and [Ru

3H(CO)

9(C

8H

11)], the organic ligands in each differ-

ing only in the transfer of one hydrogen atom. The organic ligand in the former isbonded in a conventional k

3-g2 manner while the latter is co-ordinated as a k

3-g3-

allenyl fragment.95 Thermolysis of [Ru3(CO)

12] with senecialdimine

[(CH3)2C——CHCH——NR] (R\Pr* or Bu5) gave [Ru

2(CO)

6M(CH

3)2C(H)CC(H)NRN],

[Ru2(CO)

6MC(H)C(CH

3)C(H)C(H)——NRN], the salt [2-MC(H)——C(CH

3)2N-4-

CH3C

5H

3N][Ru

6H(CO)

18], [Ru

3H(CO)

9M(CH

3)2C(H)CH

2C——NRN] and

[Ru2(CO)

6MC(H)C(CH

3)C(H)C——N(H)RN], the distribution of which depends on the

N-substituent and the reaction temperature.96Iodobenzene and 4-iodotoluene react with [Ru

3(CO)

12] to give the oxidative addi-

tion product [Ru3(k-I)(CO)

8(k-g1: g6-C

6H

4R)] (R\H or CH

3) whereas 1-iodonaph-

thalene and 9-iodophenanthrene react with dehydohalogenation to give the bridgedcluster [Ru

4(CO)

12(k

4-g2-L)] (where L\naphthyne or 9,10-phenanthyne).97 The

Me3NO-promoted reaction of (R)-2,2@-bis(diphenylphosphino)-1,1@-binaphthyl (L1)

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with [Ru3(CO)

12] unexpectedly gave the hydroxy-bridged cluster [Ru

3(k-

OH)2(CO)

8L1]. Two of the P—Ph bonds rotate freely while rotation of the remaining

two is restricted. In the absence of Me3NO, (R)-L1 reacts with [Ru

3(CO)

12] to give

[Ru3(k-H)(CO)

9Mk

3-(C

6H

4)PPhC

20H

12PPh

2N], the first example of an orthometal-

lated 2,2@-bis(diphenylphosphino)-1,1@-binaphthyl complex.98 Reaction of[Ru

3(CO)

12] with 1-methylpyrrole gave [Ru

3(k-H)(CO)

9(k

3-g3-C

4H

3NMe)] 45 as a

mixture of two interconverting isomers, the dynamic equilibrium involving a hydrideshift between Ru—Ru edges and a 1,2 double-bond shift within the k

3-ligand (Scheme

N

(CO)3Ru Ru(CO)3

Ru H

MeH

HH

N

(CO)3Ru Ru(CO)3

Ru

MeH

H

H

H

(CO)3(CO)3

45b45a

Scheme 10

10). Similarly, 1,2,5-trimethylpyrrole and 2,5-dimethylpyrrole react with [Ru3(CO)

12]

in refluxing thf to afford [Ru3(k-H)(CO)

9Mk

3-g3-C

4H(Me

2)NMeN] and [Ru

3(k-

H)(CO)9Mk

3-g3-C

4H(Me

2)NHN] respectively, in a single isomeric form. In refluxing

toluene 2,5-dimethylpyrrole reacts with [Ru3(CO)

12] to give [Ru

3(k-H)(CO)

9Mk

3-g3-

CH——C4H

2(Me)NN] and [Ru

3(k-H)(CO)

9(k-CO)Mk

3-g2-CHC

4H

2(Me)NN] via N—H

and C—H (methyl) activation and loss of H2.99 The first example of the reversible

activation of a triphenylphosphine C—H bond has been reported. Thermolysis of the48-electron cationic cluster [Ru

3(CO)

8(PPh

3)2(k3-ampy)]` 46 gives the phenyl deriva-

tive [Ru3(k-Ph)(CO)

7(k-PPh

2)(PPh

3)(k

3-ampy)]` 47 which readily adds CO to regen-

erate the starting material, via the 50-electron cluster [Ru3(k-Ph)(CO)

8(k-

PPh2)(PPh

3)(k

3-ampy)]` 48 (Scheme 11). Treatment of [Ru

3(k-Ph)(CO)

7(k-

PPh2)(PPh

3)(k

3-ampy)][BF

4] with [N(PPh

3)2]Cl results in migratory insertion

of CO to give the neutral acyl cluster [Ru3(CO)

5(PPh

3)Mk-C(O)PhN(k-PPh

2)(k

3-

ampy)].100Two moles of phenylacetylene react with the azavinylidene cluster [Ru

3(k-

H)(CO)10

(k-N——CPh2)] to give the binuclear derivative [Ru

2(CO)

4(k-CO)Mk-

PhC——CPhCPh——CPhNPh(C6H

4)N] via stepwise insertion of PhC———CH into Ru—N and

Ru—C bonds.101 The 48-electron cluster cations [Ru3(CO)

10(k

3-ampy)][BF

4] react

with Cl~, I~ or CH3CO

2~ to afford the neutral 50-electron species [Ru

3(CO)

9(k-

X)(k3-ampy)] while reaction with NaBH

4affords the neutral hydride derivative

[Ru3(k-H)(CO)

9(k

3-ampy)]. Condensation of [N(PPh

3)2]2[Ru

3(CO)

9(k

3-S)] with

[Ru3(CO)

10(k

3-ampy)][BF

4] gave the hexanuclear cluster [Ru

6(k-H)(CO)

17(k

4-S)(k

3-

ampy)] which contains a square planar Ru4

unit in which two opposite edges arebridged by additional ruthenium fragments.102

The reaction of ruthenium and osmium k3-g2-imidoyl clusters with alkynes has been

reported. At 70 °C, [Ru3(k-H)(CO)

9(k

3-g2-CH

3——NCH

2CH

3)] and [Ru

3(k-

H)(CO)9(k

3-g2-C——N(CH

2)3] react with but-2-yne to give [Ru

3(CO)

7(k

3-g2-g4-

C4(CH

3)4N(k-g2-CH

3C——NCH

2CH

3)Mg1-COC(CH

3)C(H)CH

3N] and [Ru

3(CO)

8Mk-g2-

C——N(CH2)3N(k-g2-CH

3C(H)——CCH

3)] respectively. Hydrometallation of but-2-yne

423Organometallic chemistry of bi- and poly-nuclear complexes

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Ru Ru

Ru

N

Ph3P

N Me

P

H

Ru Ru

Ru

N

Ph3P

N Me

P

H

Ru Ru

Ru

N

PPh3

Ph3P

N MeH

Ph2

Ph2

46

++

47

48

+

+CO

roomtemperature

heat

Scheme 11 Carbonyls omitted for clarity

with [Os3(k-H)(CO)

9(NCMe)Mk-g2-C——N(CH

2)3N] gave [Os

3(CO)

8Mk-g2-

C——N(CH2)3NMk-g2-CH

3C(H)——CCH

3N] via [Os

3(CO)

9Mk

3-g2-C——N(CH

2)3NMk-g2-

CH2C——C(H)CH

3N] and [Os

3(CO)

9Mg1-C——N(CH

2)3NMk-g2-CH

3C——C(H)CH

3N]. In the

presence of Me3NO, [Os

3(k-H)(CO)

10Mk

3-g2-C——N(CH

2)3N] reacts with but-2-yne via

alkyne—imidoyl coupling to give [Os3(CO)

8Mk

3-g6-CH

3C(H)——C(CH

3)C(CH

3)——

C(CH3)C——N(CH

2)3N].103 The reactivity and ligand dynamics of the k

3-g2-imidoyl

clusters [Ru3(k-H)(CO)

9(k

3-g2-RC——NR@)] [R\Me, R@\Et or (CH

2)3;

R\R@\ Me] have been compared with their osmium analogues. Variable-tempera-ture 13C NMR spectroscopy revealed the lowest energy exchange process to be thewindshield wiper motion while axial—radial carbonyl exchange at the nitrogen-boundruthenium atom is the second fastest process. The phosphine and isocyanide substitu-tion products [Ru

3(k-H)(CO)

8L(k

3-g2-RC——NR@)] [R\Me, R@\Et, L\ PPh

3or

MeNC; R \R@\ (CH2)3, L\PPh

3or MeNC] have been prepared via k

3-k-k

3imidoyl co-ordination.104

Two products were isolated and crystallographically characterised from the ther-molysis of [Ru

3(CO)

7(k-CO)(k-dppm)(k-PhC———CC———CPh)]. The first of these,

[Ru3(CO)

8(k-dppm)Mk

3-CPhC(H)CC(C

6H

4-2)N] results from orthometallation of a

phenyl ring and Ru—Ru bond cleavage while the second, [Ru3(CO)

5(k-CO)(k-

dppm)(k3-C

4H

2Ph

2)], contains a partially hydrogenated diyne chelated to a single

metal centre. In comparison, thermolysis of the unsubstituted cluster [Ru3(CO)

9(k-

CO)Mk3-PhC

2C———CPh)] gave [Ru

4(CO)

n(k

4-PhC

2C———CPh)] (n\ 12 or 14).105 The re-

action of an excess of P———CBu5 with [Ru3(CO)

10(k-dppm)] gave [Ru

3(CO)

7(k-

dppm)Mk3-PC——C——O)Bu5N

2], a 50-electron cluster capped by two k

3-ketenylphos-

phinidene ligands.106The triosmium cluster [Os

3(CO)

9(k

3-g2: g2 :g2-HN——C

6H

5Ph)], containing a novel

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side-on co-ordinated imine ligand, has been prepared by abstraction of H~ from thesubstituted aminocyclohexadienyl cluster [Os

3(CO)

9(k

3-g2 : g1 : g2-C

6H

5PhNH

2)].107

The photochemistry of [Ru3(CO)

12] with nitrogen heterocycles has been studied. In

all cases products of substitution were isolated, although in the case of pyridine and2-methylpyridine orthometallated products of the type [Ru

3(k-H)(CO)

10(C

5H

3RN)]

(R\ H or Me) were obtained. It appears that heterocycles inhibit the photo fragmen-tation pathway common for donor solvents such as diethyl ether and diethyl acet-ate.108 Addition of methylpropiolate to [Os

3(CO)

10(CNPr)(NCMe)] results in re-

gioselective alkyne—carbonyl and alkyne—isocyanide coupling to give [Os2(CO)

6Mk-

g2 : g3-C(OH)C(CO2Me)——CHCNHPrN] as the major product and [Os

2(CO)

6Mk-

g2 : g3-C(OH)CH——C(CO2Me)CNHPrN] as a minor isomer.109 The triosmium cluster

[Os3(k-H)(CO)

9(k

3-Bu/OC——CHPEt

2)] catalyses the silylation of terminal olefins with

Et3SiH to give the corresponding trans-triethylvinylsilane and alkanes.110 The elec-

tron-deficient cluster [Os3(k-H)(CO)

9Mk

3-g2-C

9H

5(Me)NN] reacts with thiols, RSH, to

give [Os3(k-H)(H)(CO)

9(k-SR)Mk

3-g2-C

9H

5(Me)NN] which readily decarbonylates to

give [Os3(k-H)

2(CO)

8(k-SEt)Mk-g2-C

9H

5(Me)NN], [Os

3(k-H)(CO)

10(k-SEt)] and

[Os3(k-H)

2(CO)

9(k

3-S)].111 The Ru

3triangle in [Ru

3(CO)

9(k-g2 : g2 :g2-C

70)] is co-

ordinated to only one of the three possible six-memebered rings. Likewise both Ru3

triangles in [MRu3(CO)

9k-g2 : g2 : g2N

2C

70] are bonded to the same type of six-mem-

bered ring.112The high-temperature reaction between thionylaniline and [Os

3(CO)

12] gave

[Os3(CO)

9(k

3-NPh)(k

3-S)] while under more mild conditions using

[Os3(CO)

10(NCMe)

2] as a precursor gave [Os

3(CO)

9Mk

3-g2-(PhN)

2SON(k

3-S)] which

contains a triply-bridging sulfide and a bis(phenylimino)oxo-j6-sulfone group.113The thermolysis of [Fe

2(CO)

6(k-PPh

2)(k-g1 :g2-C———CPh)] 49 affords [Fe

4(CO)

8(k-

PPh2)2(k-g1 : g1 : g2 : g2-C———CPh)

2] 50 with two face-capping acetylides linked through

the Fe4

face by a short carbon—carbon contact. Further reaction with CO results inC—C and C—P bond formation to give [Fe

3(CO)

8Mk-Ph

2PC(CPh)——C(CPh)PPh

2N] 51

(Scheme 12).114 The synthesis and molecular and electronic structure of the tetranuc-lear k-vinylidene cluster [Fe

4(CO)

12(k

4-C——CHMe)] has been described. The cluster

(CO)3Fe Fe(CO)3

CC

PPh2

Ph

Fe Fe

CFe

C P

CCPh2P

Ph

Ph

Fe FeFeFe

CC

Ph

CC

Ph

PPh2

Ph2P

Ph2

515049

Scheme 12

has an open butterfly arrangement of metal atoms with the organic fragment bondedto all four. The geometry of the [Fe

4C——CHMe] core results from overlap between the

formal C——C double bond and the two wing-tip iron atoms and causes the cluster toclose up around the vinylidene fragment.115 Protonation of the 62-electron nidocluster [Ru

4(CO)

13(k

3-PNPr*

2)] gave the hydroxyphosphinidene organometallic clus-

ter acid [Ru4(CO)

13(k

3-POH)]. The square Ru

3P face of this cluster can be capped

with [Pt(PPh3)2(C

2H

4)] to give the 74-electron closo-octahedral Ru

4PtP cluster

[Ru4Pt(CO)

13(PPh

3)(k

4-POH)].116 The 62-electron butterfly cluster [Ru

4(CO)

13(k

3-

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PPh)] reacts with phosphaalkynes RC———P (R\Bu5 or C6H

2Bu5

3-2,4,6) to give a series

of unsymmetrically capped bis(phosphinidene) clusters containing a ketene sub-stituted k

4-PR ligand. The initial product of phosphaalkyne reaction is the open chain

compound [Ru4(CO)

12(k

3-PPh)Mk

3-PC(CO)RN] which eliminates CO to give

[Ru4(CO)

10(k-CO)(k

4-PPh)Mk

4-PC(CO)CRN]. In the case of 2,4,6-Bu5

3C

6H

2, this lat-

ter cluster readily loses a ruthenium carbonyl vertex to give nido-[Ru3(CO)

9(k

4-

PPh)Mk3-PC(CO)C

6H

2Bu5

3-2,4,6N].117

Addition of trimethyl phosphite to [Os4Ru(k-H)

2(CO)

12(g6-C

6H

6)] affords

[Os4Ru(k-H)

2(CO)

12MP(OMe)

3N(g6-C

6H

6)] which rearranges in solution to give

[Os4Ru(k-H)

3(CO)

12MP(OMe)

3N(k

3-g6-C

6H

5)], containing a ruthenium-spiked Os

4tetrahedral skeleton with one of the arene carbon atoms bridging an Os—Os edge andthe ring g6-co-ordinated to the Ru atom.118 The tetrahedral cluster [Ru

4(CO)

7(k-

C7H

7)2] contains a tetrahedron of ruthenium atoms sandwiched between two cy-

cloheptatrienyl ligands.119 The products of thermolysis of [Ru3(CO)

12] with styrene,

4-methylstyrene and 4-trifluoromethylstyrene have been characterised. In each casecompounds of the type [Ru

4(CO)

12(k

4-g1 : g1 : g2 : g2-HCCC

6H

4R)], [Ru

3(CO)

8(k

3-

g6 : g2 : g1 : g1-HCC(H)C6H

3R)] and [Ru

6C(CO)

14(g6-MeC

6H

4R)] have been isolated.

A comparison with the reaction of isopropenyl benzene revealed a vastly differentproduct distribution.120

The dicarbide clusters [Ru5(CO)

12(k

5-C

2)(k-SMe)

2(k-PPh

2)2] and [Ru

5(CO)

11(k

5-

C2)(k-SMe)

2(k-PPh

2)2] have been isolated from P—C bond cleavage reactions of the

linear bis(tertiary phosphine) cluster [MRu3(CO)

11N2Mk-C

2(PPh

2)2N] via the thermoly-

sis product [Ru5(k

5-C

2PPh

2)(CO)

13(k-PPh

2)].121 Carbonylation of [Ru

5(CO)

11(k

5-

C2)(k-SMe)

2(k-PPh

2)2] resulted in Ru—Ru bond cleavage to give [Ru

5(CO)

13(k

4-

C2)(k-SMe)

2(k-PPh

2)2], the C

2ligand of which bridges one edge of a Ru

3triangle and

an isolated Ru2fragment.122 The electronic and geometrical structures of a wide range

of M5C

2and M

6C

2clusters containing expanded C

2ligands have been analysed and

compared. The C2

fragment interacts strongly with the metal cage via electron dona-tion from C

2FMO’s into vacant metal-based molecular orbitals, supplemented by

donation from filled metal-based MO’s to C2

n*g orbitals (Dewar—Chatt—Duncansonmodel).123 Thermolysis of [MRu

3(k-H)(CO)

8(k

3-C

2Bu5)N

2Mk-C

2(PPh

2)2N] results in

C—C bond formation with partial hydrogenation of the C2Bu5 group to give

[Ru6(CO)

13(k

5-Bu5CH——CHC

2PPh

2)(k

4-C

2Bu5)(k-PPh

2)2] and [Ru

6(CO)

12(k-

CO)(k6-C

2CH——CHBu5)(k

3-C

2Bu5)(k-PPh

2)2].124 Addition of phen and bipy to

[Ru5C(CO)

15] results in loss of only one CO to give the bridged butterfly clusters

[Ru5C(CO)

14(phen)] and [Ru

5C(CO)

14(bipy)] respectively. In both cases, further loss

of CO and orthometallation gave [Ru5(k-H)C(CO)

13(C

12H

7N

2)] and [Ru

5(k-

H)C(CO)13

(C10

H7N

2)], rather than the expected 74-electron square-based pyramidal

clusters [Ru5C(CO)

13(phen)] and [Ru

5C(CO)

13(bipy)].125 The cluster dianion

[Ru5C(CO)

14]2~ reacts with two equivalents of [Ru(NCMe)

3Cp]` to afford

[Ru6C(CO)

14Cp]~ and [Ru

7C(CO)

14Cp

2]. Similarly [Ru

6C(CO)

16]2~ may be cap-

ped by the [RuCp]` fragment to give the heptanuclear monoanion [Ru7C(CO)

16Cp]~. In each case the cluster skeletons are based on a central Ru

6C octahedral core.

These are not simple ionic coupling reactions since products of arene transfer have alsobeen isolated.126 The stepwise synthesis of [Ru

6C(CO)

13(g5-C

5H

3Ph

2)(k

3-CPh)] has

been described. Reaction of [Ru6C(CO)

17] with Me

3NO and PhC———CH affords

[Ru6C(CO)

15(k

3-g2-PhC———CH)], which reacts with excess phenylacetylene in the pres-

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ence of Me3NO to afford two isomers [Ru

6C(CO)

14Mk

3-C(Ph)CHC(Ph)CHN] and

[Ru6C(CO)

14Mk

3-C(Ph)CHCHC(Ph)N] via coupling of two molecules of phenylacety-

lene. Finally, the former isomer reacts with Me3NO and phenylacetylene to afford

[Ru6C(CO)

13(g5-C

5H

3Ph

2)(k

3-CPh)] via C———C scission and C—C bond formation.127

Treatment of a hexane solution of [Ru6C(CO)

17] with the organodiphosphines

Ph2P(CH

2)nPPh

2(n\ 1—3) gave [Ru

6C(CO)

15Mk-Ph

2P(CH

2)nPPh

2N], with the

diphosphine bridging one Ru—Ru edge of an octahedral skeleton.128 The fluxionalityof the hexanuclear clusters [Ru

6C(CO)

14(SO

2)(k-g3-C

3H

5)]~, [Ru

6C(CO)

14(NO)(k-

g3-C3H

5)] and [Ru

6C(CO)

14(NO)(k-g3-C

3H

4CO

2Me)] has been interpreted in terms

of rapid migration of the SO2

and NO ligands over the metal cluster core rather thanmotion of the g3-co-ordinated allyl group.129 A variety of arene—alkyne derivatives ofthe Ru

6C fragment have been prepared including; [Ru

6C(CO)

12(g6-C

6H

6)(k

3-

C2Me

2)], [Ru

6C(CO)

12(g6-C

6H

5Me)(k

3-C

2Me

2)], [Ru

6C(CO)

12(g6-C

6H

4Me

2-

1,3)(k3-C

2Me

2)], [Ru

6C(CO)

12(g6-C

6H

3Me

3-1,3,5)(k

3-C

2Me

2)] and

[Ru6C(CO)

12(k

3-C

16H

16)(k

3-C

2Me

2)].130 Treatment of [Ru

6C(CO)

17] with two

equivalents of Me3NO in the presence of but-2-yne gave [Ru

6C(CO)

15(k

3-g1 : g2 : g1-

C2Me

2)] and the more highly substituted cluster [Ru

6C(CO)

14(k

3-g2 : g2-C

2Me

2)(k

3-

g1 : g2-g1-C2Me

2)] which rearranges from an Ru

6octahedron to a mono-capped

square-based pyramidal structure. Further treatment of [Ru6C(CO)

15(k

3-g1 : g2-g1-

C2Me

2)] with Me

3NO and but-2-yne gave [Ru

6C(CO)

14(k

3-g2 : g2-C

2Me

2)(k

3-g1: g2-

g1-C2Me

2)] together with low yields of [Ru

6C(CO)

12(k

3-g1 : g2-g1-C

2Me

2)3]. Loss of

CO (heat or Me3NO) from [Ru

6C(CO)

15(k-g2 : g2-C

2Me

2)(k

3-g1 : g2-g1-C

2Me

2)] re-

sults in a further skeletal rearrangement to give the octahedral cluster [Ru6C(CO)

13(k-

g1 : g2-g1-C2Me

2)2].131

6 Cobalt, rhodium and iridium

Cyclopentanones are formed in the reductive Pauson—Khand reaction of co-balt—alkyne complexes [Co

2(CO)

6(k-RC———CH)] with norbornene in the presence of

trifluoroacetic acid.132 The scope of the intramolecular Pauson—Khand reaction withFischer carbene metal complexes has been reported. In particular alkynyl(al-lylamino)carbene complexes of Cr and W0 52 afford good yields of the expectedcycloadducts 53. The influence of steric and electronic effects as a result of substitutionat different sites of the enyne chain and the effect of different heteroatoms have beenstudied.133

N

(CO)5WN

H

Ph

[Co2(CO)8]

52 53

H

(CO)5W

O

Ph

The pyrylium cation [Co2(CO)

6(k-g2 : g2-C

5OH

2Ph

2C———CR)]` was obtained by

hydride abstraction from the corresponding pyran complex [Co2(CO)

6Mk-g2: g1-

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(C5OH

3Ph

2)C———CRN] (R\ H or Ph) and the reactivity of these complexes toward

selected nucleophiles has been reported.134 exo Cluster substitution of B—H in themetallaborane closo-[2,3,4-Cp*

3(k-H)

2Co

3B2H

2] with [MCoClCp*N

2] and FeCl

3gave

closo-1-Cl-[2,3,4-Cp*3(k-H)

2Co

3B2H] and closo-1,5-Cl

2-[2,3,4-Cp*

3(k-H)

2Co

3B2]

respectively, whereas hydrolysis gave closo-1-OH-[2,3,4-Cp*3(k-H)

2Co

3B2H].135

The phosphinoalkynes Ph2PC———CR (R\H, Me, CF

3, Bu5, Ph or PPh

2) co-ordinate

to [Rh2(k-CO)(k-g2 : g2-CF

3C———CCF

3)Cp

2] as tertiary phosphines. In the case of

R\Me or H, oxygen-atom transfer and intramolecular condensation gave the phos-phino—enone derivative [Rh

2Mk-C(CF

3)C(CF

3)CC(O)RPPh

2NCp

2].136 The hy-

drodesulfurisation of thiophene and benzothiophene by [MIr(H)ClCp*N2] has been

examined. Thiophene and benzothiophene react with [MIr(H)ClCp*N2], in the presence

of H2, to give the hydrogenolysis products [MIrClCp*N

2(k-H)(k-SC

4H

9)] 54 and

[MIrClCp*N2(k-H)(k-SC

6H

4Et-2)] 55 respectively. High-temperature thermolysis of

these thiolate-bridged products under a H2

pressure gave the desulfurised products,butane and ethylbenzene respectively.137

Ir IrS

HCl

Cp* Cp*

ClIr Ir

S

HCl

Cp* Cp*

Cl

54 55

The isocyanide complexes [MRh(k-pz)(CNBu5)2N2] and [MM(k-L)(CNBu5)

2N2]

(M\Rh or Ir; L\SBu5) react with MeI via a double oxidative addition reaction toafford, for example, [MRh(k-pz)(Me)(CNBu5)

2N2(k-I)]I whereas the mixed-ligand com-

plexes [(cod)M(k-pz)2M(CNBu5)

2] (M\Rh or Ir) react with a single equivalent of

MeI to generate mixed valence compounds of the type [(cod)Rh(k-pz)

2Rh(Me)I(CNBu5)

2] and [(cod)(Me)Ir(k-pz)

2(k-I)Ir(Me)(CNBu5)

2]I.138 Cowie and

co-workers have reported the synthesis and characterisation of vinyl, vinyl hydrideand vinyl alkyl heterometallic complexes of Rh and Os. Hydrometallation of propyneand Me

2C——C——CH

2with [RhOs(H)(CO)

3(k-dppm)

2] gave [RhOsMC(Me)——

CH2N(CO)

3(k-dppm)

2] and [RhOsMC(Me)——CMe

2N(CO)

3(k-dppm)

2] respectively,

whereas reaction with allene gave [RhOsMC(Me)——CH2N(CO)

3(k-dppm)

2] and low

yields of the g3-allyl derivative [RhOs(g3-C3H

5)(CO)

3(k-dppm)

2]. Under a CO atmos-

phere [RhOsMC(Me)——CH2N(CO)

3(k-dppm)

2] undergoes migratory insertion to give

the isopropenoyl complex [RhOsMC(O)C(Me)——CH2N(CO)

3(k-dppm)

2], which proto-

nates first at the metal centre to give the hydride [RhOs(k-H)MC(O)C(Me)——CH

2N(CO)

3(k-dppm)

2][BF

4] and then, in the presence of excess acid,

at the acyl oxygen to generate the carbene [RhOs(k-H)M——C(OH)C(Me)——CH2N(CO)

3(k-

dppm)2][BF

4]2. Similarly, the vinyl complex [RhOsMC(Me)——CH

2N(CO)

3(k-dppm)

2]

reacts with MeSO3CF

3to form [RhOsMeMC(Me)——CH

2N(CO)

3(k-dppm)

2][CF

3SO

3]

which protonates at low temperature to afford the binuclear carbene[RhOsMe(——CMe

2)(CO)

3(k-dppm)

2][X][Y] (X\Y \BF

4; X\BF

4,

Y\CF3SO

3).139

Despite a formal Ir——Ir double bond the dimer [MIr(k-CO)Cp*N2] does not react with

HCl but is protonated by HBR@4·2Et

2O [R@\ 3,5-(CF

3)2C

6H

3] to give

[MIr(CO)Cp*N2(k-H)]` and [MIr(CO)Cp*(k-H)N

2]2`. The monocation reacts with CO

428 S. Doherty

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and H2

to give [MIr(CO)Cp*N2(k-CO)(k-H)]` and [MIr(CO)HCp*N

2(k-H)]` respect-

ively. The latter reaction is a rare example of oxidative addition of H2

across ametal—metal multiple bond. Deprotonation of [MIr(CO)HCp*N

2(k-H)]` gave

[MIr(CO)(H)Cp*N2] which contains an unsupported Ir—Ir bond. In contrast, direct

reaction of [MIr(k-CO)Cp*N2] with H

2results in slow formation of the monomer

[Ir(CO)(H)2Cp*].140

The amido-bridged dinuclear IrIII and IrII complexes [Ir2(k-X)Mk-C

10H

6(NH)

2-

1,8NCp*2]X and [Ir

2Mk-C

10H

10(NH)

2-1,8NCp*

2] respectively have been prepared

from [MIr(k-X)Cp*N2] and the corresponding lithium amide.141 Prolonged reaction of

triphenylsilane and [HSi(C6H

4OCF

3-p)

3] with [RhClL

2] (L \PPr*

3) led to the for-

mation of [MRh(H)L(SiR3)N

2(k-Cl)(k-H)], and possible reaction pathways have been

described.142 In the absence of a donor ligand photolysis of [Co2(CO)

8] with 2,2@,5,5@-

tetra-tert-butyl-1,1@-biphosphole (L) gave the metal—metal double-bonded dimer[MLCo(CO)N

2] which reacts with ethyldiazoacetate to give the phospholyl-supported

carbene [MLCo(CO)N2(k-CHCO

2Et)].143 Carbon—carbon bond cleavage of bipheny-

lene with [M(C2H

4)2Cp*] (M\Rh or Co) gave [M

2RCp*

2] (R\ 2,2-biphenyl) in

which the bridging hydrocarbon is p-bonded to one metal and g4-co-ordinated to theother. Variable-temperature NMR studies revealed a fluxional process that exchangesthe Cp* rings by interchanging the p- and n-bonding of the biphenyl ligand.144Prolonged reflux (3—4 days) of 2,5-disilahexane with [Co

2(CO)

8] gave [Co

2(CO)

6Mk-

CH3Si(CH

2)2SiCH

3N], a Co

2Si

2butterfly cluster with an unusually short Si · · · Si

transannular distance of 2.691(2) Å.145Reaction of [M(NCMe)

3Cp*][PF

6]2

(M \Rh or Ir) with the persulfido ligand in[Ru

2S4Cp*

2] gave [MRu

2(NCMe)S

4Cp*

3][PF

6]2, which was shown by NMR stu-

dies to be stereochemically non-rigid, undergoing racemisation via the base-free inter-mediate [MRu

2S4Cp*

2]2` in which one of the S—S bonds has been cleaved.146 The

solvent dependence of the reaction between [Ir(CO)2Cp*] and aryldiazonium ions

[N2R][BF

4] (R\C

6H

4OMe-p) has been examined and found to give the nitrogen

extrusion product [Ir(CO)2(R)Cp*][BF

4] in acetone, the binuclear product

[Ir2(CO)

3Cp*

2][BF

4] in dichloromethane and the aryldiazene adduct

[Ir(CO)(OEt)(NHR)Cp*][BF4] in ethanol.147

Cyclopentadienyl-based tricobalt clusters containing a k3-cyclic furyne ligand

CH2C———CCH

2O have been prepared by pyrolysis of the butynediol complex

[Co3(CO)(k-RC———CR)Cp

3] (R\ CH

2OH). Variable-temperature NMR studies have

shown that the alkyne undergoes rotation on the Co3

face and activation parametershave been determined [*G8 (300K)\ 39.4(2) kJmol~1, *S8 \[ 18(2) Jmol~1 and*H8 \ 34.0(4) kJmol~1].148 The phosphonate-functionalised methylidyne cluster[Co

3(CO)

9Mk

3-C-P(O)(OR)

2N] (R\Et or SiMe

3) co-ordinates to Lewis-acid metal

complexes such as [MClCp2]` (M \ Ti or Zr) through the oxygen lone pair.149

Thermolysis of the secondary phosphine substituted cluster [Co3(CO)

8(PPh

2H)(k

3-

CR)] (R\Me or CO2Me) gave [Co

3(k-H)(CO)

7(k-PPh

2)(k

3-CR)] while its disub-

stituted counterpart gave [Co3(CO)

6(Ph

2PH)(k-Ph

2POPPh

2)(k

3-CR)] (R \Me) in

which P—O bond formation has occurred. Direct treatment of [Co3(CO)

9(k

3-CR)]

with P2Ph

4also gave the P—O coupled product [Co

3(CO)

7(k-Ph

2POPPh

2)(k

3-CR)]

via the intermediates [Co3(CO)

8(P

2Ph

4)(k

3-CR)] and [Co

3(CO)

7(k-P

2Ph

4)(k

3-CR)].

The origin of the oxygen was uncertain but expected to be air or oxygen.150Various metal electrophiles react with [Ir

3(k-CO)

3(g5-C

9H

7)3] to give

429Organometallic chemistry of bi- and poly-nuclear complexes

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[Ir3MM(PPh

3)N(CO)

3(g5-C

9H

7)3][PF

6] (M\Cu, Ag or Au), [Ir

3Tl(k-CO)

3(g5-

C9H

7)3][PF

6] and [Ir

3(HgPh)(CO)

3(g5-C

9H

7)3][PF

6]. The mixed iridium—thallium

cluster maintains C37

symmetry in which the triangular arrangement of Ir atoms isface-cappedby the thallium atom. The cuboidal clusters [MM(k

3-S)Cp*N

4] (M\ Rh or

Ir) have been isolated by dehydrohalogenation of [MMClCp*N2(k-SH)

2] with NEt

3,

whereas condensation with [Pd(PPh3)4] and [MRhCl(cod)N

2] gave heterometallic

derivatives.151

8 Nickel, palladium and platinum

Metathesis of Cl~ by OH~ in [Pd2(PEt

3)2R

2(k-Cl)

2] gave [Pd

2(PEt

3)2R

2(k-OH)

2] as

a mixture of syn and anti isomers. Further reaction of [Pd2(PEt

3)2R

2(k-OH)

2] with

3,5-dimethylpyrazole gave anti-[Pd2(PEt

3)2R

2(k-dmpz)

2] while cleavage of the hy-

droxy bridge with PEt3gave [Pd

2(PEt

3)2R(OH)] as a cis/trans mixture of isomers and

reaction with NH2Ph gave the amido—hydroxy palladium dimer [Pd

2(PEt

3)2R

2(k-

OH)(k-NHPh)].153 Carbonylation of [NBu4]2[MPt

2(C

6F5)2(k-Cl)(k-PPh

2)2N2] gave

[NBu4][(C

6F5)2Pt(k-PPh

2)2PtCl(CO)] from which Cl~ can be removed to give

[Pt4(C

6F5)4(CO)

2(k-PPh

2)4]. Although [NBu

4]2[MPtPd(C

6F5)2(k-Cl)(k-PPh

2)2N2]

does not react with CO, treatment with AgClO4

gave [Pt2Pd

2(C

6F5)3(PPh

2C

6F5)(k-

PPh2)3] which takes up CO to give [Pt

2Pd

2(C

6F5)3(CO)(k-PPh

2)2Mk

3-PPh(1,2-g2-

Ph)-i3PN(PPh2C

6F5)].154 Reaction of mononuclear hydride complexes of the type

trans-[Pt(H)XL2] (X\C———CPh, Cl or C

6F5) with cis-[Pt(C

6F5)2(thf)

2] has been used

to prepare binuclear compounds with mixed bridging ligands. For instance, trans-[PtH(C———CPh)(PPh

3)2] reacts with cis-[Pt(C

6F5)2(thf)

2] to give trans-

[Pt(C6F5)(PPh

3)(k-H)(k-C———CPh)Pt(H)(PPh

3)2] while trans-[PtH(C

6F5)(PPh

3)2] in-

itially gave trans,cis-[Pt(C6F5)(PPh

3)(k-H)Mk(P)-g2-PPh

3NPt(C

6F5)2] which subse-

quently rearranges to give cis-[Pt(C6F5)(PPh

3)(k-H)(k-C

6F5)Pt(C

6F5)(PPh

3)].155

The dimeric palladium complex [MPd(Ph)(PPh3)(k-OH)N

2] reacts with NH

2R via

proton exchange to afford the binuclear palladium amido complexes[MPd(Ph)(PPh

3)N

2(k-OH)(k-NHR)] and [MPd(Ph)(PPh

3)(k-NHR)N

2]. The mechanism

was proposed to involve cleavage of the dimer by association of amine, reversibleproton transfer to give an amido ligand and a bound water, reassociation of the amidomonomer with one of the original hydroxide monomers, and displacement of waterand amine.156 Exchange of the bridging buta-1,3-diene ligand in [Pd

2Cl(k-Cl)Mk-

g2 : g2-H2C——C(H)C(H)——CH

2N] by the g1 substituted butadienyl complex

[PdCl(PPh3)2Mtrans-g1-H

2CC(Me)C——CH

2N] gave the tripalladium cluster [Pd

2(k-

Cl)(PPh3)2Pd(PPh

3)Cl

2Mk-H

2C——C(Me)C——CH

2N].157 The bis(phosphonate)pla-

tinum() complex [Pt(dppm)MP(O)(OMe)2N2] reacts with [PtMe

3I] to give

[Pt(dppm)Mk-[P(O)(OMe)2]N

2(k-I)PtMe

3], which when treated with AgPF

6and

PPh3affords the cation [Pt(dppm)Mk-[P(O)(OMe)

2]N

2PtMe

3(PPh

3)][PF

6]. Mixtures

of [MPd(k-Cl)(g3-C3H

4Me-2N

2] or [MRh(k-Cl)(cod)N

2] with silver perchlorate react

with [Pt(dppm)MP(O)(OMe)2N] to give [Pt(dppm)Mk-[P(O)(OMe)

2]N

2Pd(g3-

C3H

4Me-2)][ClO

4] or [Pt(dppm)Mk-[P(O)(OMe)

2]N

2Rh(cod)][ClO

4] respec-

tively.158 Grignard reagents of bulky organic groups such as mesityl and trimethylsilylreact with [PdX

2(dppm)] (X\Cl or Br) to give [PdR

2(dppm)]. With smaller alkyl

groups the halide-bridged A-frame complexes [Pd2(k-X)R

2(k-dppm)

2]` (R\ Me, Et,

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Bu or CH2Ph) were formed. Similar dimers can be prepared by reacting

[Pd(CH2SiMe

3)2(dppm)] with HCl. The dialkyl complex [PdR

2(dppm)], containing

small aryl groups, readily reductively eliminates R—R to form [Pd2X

2(dppm)

2] via

association with [PdX2(dppm)].159

The palladium clusters [Pd4(k-Cl)

2(PBu5

3)4(k

3-CH)] and [Pd

2(k-X)(PBu5

3)2]

(X\ Br or I) act as a source of XPdPBu53which readily reacts with [Co

2(CO)

8] to give

[Pd3Co(k-X)(k-CO)

3(CO)(PBu5

3)3] (X\Cl, Br or I).160 The diplatinum complex

anti-[Pt2(k-dpmp)

2(CNR)

2][PF

6]2reacts with [M

3(CNR)

6] (M\Pd or Pt) to afford

the trimetallic A-frame cluster [Pt2M(CNR)

2(k-dpmp)

2][PF

6]2

via insertion of[M0(CNR)

2] into the Pt—Pt p bond.161 The anionic tetranuclear cluster [NBu

4]-

[Pd4(k-X)

4(C

6F5)4(k-PPh

2)2] has been prepared and its reactivity described. Mono-

dentate (L) and bidentate (L—L) ligands afford the binuclear derivatives [Pd2(k-Cl)

(C6F5)2(k-PPh

2)L

2] or [Pd

2(C

6F5)2(k-PPh

2)(L—L)]n (L\PPh

3, py, n\ 0;

L—L\ acac, n\ [ 1; L—L\bipy or phen, n\] 1).162 Reaction of [Pt3(k-

CO)3(PCy

3)3] and [Pt

3(k-CO)(k-CNxyl)(CNxyl)(PCy

3)2] with [(MPR@

2)2R]2`

[M\Cu, Ag or Au; R \C6H

4, (CH

2)2C

6H

4or FeCp; R@\ C

6H

5or C

6H

11] gave

[MPt3(k-CO)

3(PCy

3)3N2M(MPR@

2)2RN]2` and [MPt

3(k-CNxyl)

2(k-CO)(CNxyl)-

(PCy3)2N2MM(PR@

2)2RN]2` respectively.163

9 Heterometallics

Metallation of the bridging phosphido ligand in [M2(CO)

4(k-PH

2)Cp

2]~ (M \Mo

or W) with M@LnX [M@Ln\M(CO)3Cp, X\Cl; M@Ln\W(CO)

3Cp, X \Cl;

M@Ln\Fe(CO)2Cp, X \Cl; M@Ln\Mn(CO)

5, X \Br] gave [M

2(k-H)(CO)

4(k-

PHM@Ln)Cp2] together with LnM@—M@Ln.164 The tin centres in [Fe(CO)

3(k-

Ph2Ppy)(SnPh

2)(k-Cl)(SnClPh

2)] adopt different degrees of hyper-co-ordination

which is largely evident in the different Sn—Cl bond lengths.165 Incorporation of PdCl2

into [MFe(CO)3(dppm-iP)(SnBu

2)N

2] results in rearrangement of the Fe

2Sn

2metal

core to give [Fe2(CO)

6(k-SnBu

2)(k-dppm)

2Pd] which contains a four-membered

PdFe2Sn centre with the palladium—iron bonds bridged by dppm and the two iron

atoms bridged by the stannylene ligand.166 Reaction of [CpNi(k-CO)(k-H)WCp2]

with PMe3

results in P—C bond activation to give [CpNi(k-CO)(k-PMe

2)W(Me)(PMe

3)Cp]. The proposed mechanism involves reductive elimination of

C5H

6, co-ordination of PMe

3to tungsten and oxidative addition of one of the

Ni-co-ordinated P—Me bonds.167Treatment of [TiCl(OCMe

2CH

2PPh

2)3] 56 with [MRhCl(cod)N

2] and subsequent

reduction with Na—Hg gave [Ti(k-g1 : g1-OCMe2CH

2PPh

2)3Rh] 57 with a short

Ti—Rh bond distance of 2.2142(11)Å, consistent with a Ti———Rh triple bond comprised ofone Ti(d/pp)—Rh(d/pp) and two Rh(dn)—Ti(dpn) interactions.168 Reaction ofNa

2[Fe(CO)

4] with [GaCl

2MC

6H

3(C

6H

2Pr*

3-2,4,6)

2N],168 gave [(CO)

4Fe———

GaMC6H

3(C

6H

2Pr*

3-2,4,6)

2N], the first example of a ferrogallyne. Evidence offered in

support of this formulation includes the short Fe—Ga bond distance, linear two-co-ordination about Ga and the Fe—Ga—C angle of 179.2(1)°.169

The k-alkylidene ligand in [Cp(CO)W(k-CO)Mk-C(C6H

4CH

2NMe

2)(C

6H

4Me-

p)NPdCl] is oxidised to the corresponding ketone in the presence of excess Me3NO,

whereas oxidation with two or four equivalents gave low yields of the intermediates

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TiO

Ph2P

O PPh2O

Ph2P

ClTi Rh

O PPh2

OPO PPh2Ph2

Na–Hg

56 57

1–2[{RhCl(cod)}2]

[Cp(O)W(k-CO)Mk-C(C6H

4CH

2NMe

2)(C

6H

4Mep)NPdCl] and [Cp(O)W(k-O)Mk-

C(C6H

4CH

2NMe

2)(C

6H

4Me-p)NPdCl].170 Alkylation of the heteronuclear anion

Na[Cp(CO)Fe(k-CO)2Cr(CO)(g6-C

6H

6)] with [Me

3O][BF

4] gave the methoxycar-

byne complex [Cp(CO)Fe(k-COMe)(k-CO)Cr(CO)(g6-C6H

6)]. Both the anion and

methoxycarbyne undergo cis/trans isomerisation with *G8 (300K)\ 11.5(^ 0.6) kcal mol~1 and 14.3 ( ^ 1.8) kcal mol~1 respectively. Isomerisation was sug-gested to involve an unbridged intermediate with the carbyne attached to the chro-mium rather than the iron centre. The methoxycarbyne decomposes via oxygen-to-methyl migration, possibly involving a high-energy unbridged iron carbyne com-plex.171 The heterometallic acyl and k-acyl complexes [M(CO)

4(k-PPh

2)2RhMg2-

C(O)CH(Me)(CH2)nPPh

2N] 58 and [M(CO)

3(k-PPh

2)2Mk-O——CCH(Me)(CH

2)n-

PPh2NRh(CO)] 59 (M \Cr, Mo or W) have been isolated from the reaction of

[M(CO)4(k-PPh

2)2Rh(H)(CO)(PPh

3)] 60 and the phosphinoalkenes Ph

2P(CH

2)nCH——

CH2

(n\ 1—3). Both compounds have been evaluated as catalysts in the hydrofor-mylation of diphenylphosphino-propene, -butene and -pentene.172

(CO)3M RhPPh2

PPh2

COC

PPh2

(CH2)n

HMe

(CO)4M RhPPh2

PPh2

Ph2P

C C

HMe

O

(CH2)n(CO)4M Rh

PPh2

PPh2

HPPh3

CO

60 58 59

+Ph2P(CH2)nCH CMe

CO

Bimetallic Zr—Mo and Zr—W complexes containing the bridging ligand C5H

4PPh

2have been prepared and their reaction chemistry described. For example, [ZrX(g5-C

5H

4PPh

2)(k-Cl)M(CO)

3] reacts with organolithium derivatives via substitution at

zirconium, and with neutral two-electron donor ligands via addition to the later-transition-metal centre.173 The unusual orthometallated cyclopentadienylphosphine-bridged heterometallic complexes [XCpMoM(C

5H

4)PPh(o-C

6H

4)NM(CO)

5] (X\Cl

or I; M\Cr, Mo or W) have been prepared by reacting Li[M(CO)5(PPh

2)] with the

corresponding metallocene dichloride.174 The reaction of [M@(CO)x(PPh

2)]~

(M@\Cr, Mo or W; x \ 5; M\ Fe, x \ 4) with ansa-metallocene derivatives dependson the nature of the bridging ligand. For instance, the ansa-silicon derivative[MCl

2MSiMe

2(g5-C

5H

4)2N] (M\Mo or W) gives [M(H)ClMSiMe

2(g5-C

5H

4)N(g5-

C5H

3PPh

2)M@(CO)

xN] via substitution at the 3@-position of the g5-Cp ring, while the

CMe2-bridged compound substitutes at the metal centre to give the k-phosphido

complex [MClMCMe2(g5-C

5H

4)2N(k-PPh

2)M@(CO)

x] as the dominant product.175

The character of the metal—metal bond in the phosphido-bridged complexes[M

2(CO)

8(k-PR

2)2] (M\V, Mo or Mn) has been investigated using ab initio calcula-

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tions. In the case of vanadium there is not a formal double bond but only weak partialn-bonding character. In contrast, and contrary to expectation, for M\Cr somen-bonding in addition to the p-bond is expected while for M\Mn some p- andn-bonding is present.176 Investigations of the photochemistry of[Os(CO)

4(PMe

3)W(CO)

5] indicate that the photoprocess involves heterolytic cleav-

age of the dative metal—metal bond. The major products of irradiation (j\ 400nm) inthe presence of PPh

3are [Os(CO)

4(PMe

3)], [Os(CO)

3(PMe

3)(PPh

3)] and

[W(CO)5(PPh

3)]. Irradiation in the presence of radical traps, and quantum yield

determinations for the disappearance of [Os(CO)4(PMe

3)W(CO)

5] under N

2and CO,

ruled out homolytic cleavage of the M—M bond and metal—ligand dissociation path-ways.177

Excitation of a solid sample of the binuclear IrI—CdII complex [Ir(CO)2(k-

PPh2py)CdI

2] with UV light led to a red emission at 739nm with a lifetime of 6.48ks

at 298K.178 Nucleophilic substitution of the k3-halogenomethylidyne tricobalt cluster

[Co3(CO)

6(k

3-X)(tdpm)] (X\Cl) with Na[Ru(CO)

2Cp] gave

[Co3Ru(CO)

8(tdpm)(k

4-C)Cp], the first example of a tetrahedral sp3 carbide cluster

compound or permetallated methane.179In the solid state, two isomers of the cluster anion [Ru

3Ir(CO)

13]~ differ only in the

number of bridging carbonyl ligands. Both isomers interconvert via bridge—terminalexchange of the carbonyl ligands. Protonation of [Ru

3Ir(CO)

13]~ gave

[Ru3IrH(CO)

13] while reaction with H

2gave [Ru

3Ir(H)

2(CO)

12]~.180 Substitution of

CO in the vinylidene cluster [Mo2Ru(k

3-C——CH

2)(CO)

7Cp*

2] occurs exclusively at the

Ru atom. In contrast, with PPh2H substitution to afford [Mo

2Ru(k-

C——CH2)(CO)

6(PPh

2H)Cp

2] is followed by P—H activation and hydrogen migration to

give the 46-electron alkylidyne cluster [Mo2Ru(CO)

5(k-PPh

2)(k

3-CCH

2R)Cp

2],

which reacts with another equivalent of PPh2H to regenerate the vinylidene ligand in

[Mo2Ru(CO)

4(k-PPh

2)(k

2-C——CHR)Cp

2].181Sulfidation of [Pt

3MRe(CO)

3N(k-

dppm)3][PF

6] with propylene sulfide gave [Pt

3MRe(CO)

3SN(k-dppm)

3][PF

6] and

then [Pt3MRe(CO)

3N(k

3-S)

2(k-dppm)

3][PF

6] which upon oxidation with Me

3NO or

H2O gave the oxo—sulfides [Pt

3MRe(CO)

3SN(k

3-O)(k-dppm)

3][PF

6] and

[Pt3MRe(CO)

3N(k

3-O)(k

3-S)

2(k-dppm)

3][PF

6] respectively. The mixed oxo—sulfide

clusters [Pt3MRe(CO)

3N(k

3-O)(k

3-S)(k-dppm)

3][PF

6], [Pt

3MRe(CO)

3N(k

3-O)

2(k

3-S)(k-

dppm)3][PF

6] and [Pt

3(ReO

3)(k

3-S)

2(k-dppm)

3][PF

6] have also been prepared by

sulfidation of the corresponding oxo clusters.182The mixed-metal cluster [Ru

5Rh(CO)

12(k-CO)(k4-g2-CO)

2Cp*] contains a bi-

edge-bridged tetrahedral frameworkwith the Cp* fragment at the apex of the tetrahed-ron and two k

4-g2-capping CO ligands.183 Slow addition of [Re

2(k-H)

2(CO)

8] to

[Ir(CO)(g2-C8H

14)(g5-C

9H

7)] gave [IrRe

2(k-H)

2(CO)

9(g5-C

9H

7)] which can be de-

protonated to afford the cluster anion [IrRe2(k-H)(CO)

9(g5-C

9H

7)]~. Detailed vari-

able-temperature NMR spectroscopic studies have been used to examine hydride andcarbonyl scrambling processes in both clusters.184 The chiral racemic rhenium ethynylcomplex [ReH(NO)(PPh

3)Cp*M(C———C)

nHN](n\ 1—3) reacts with

[Os3(CO)

10(NCMe)

2] with C—H activation to generate the 1-carbon bridged product

of composition [Re(NO)(PPh3)Cp*(CC)

nMOs

3H(CO)

10N]. A crystal structure determi-

nation and IR and NMR spectroscopic data support a contribution by neutralRe~(C———C)

nOs and zwitterionic Re`——(C——C)

n——Os~ resonance forms.185 The metal-

laacetylide Li[Re(NO)(PPh3)Cp*(C———C)] reacts with [Re

2(CO)

10] and [Os

3(CO)

12] to

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afford the polynuclear Fischer carbene derivatives [Re(NO)(PPh3)Cp*MC———

CC(OMe)——N MRe2(CO)

9N] and [Re(NO)(PPh

3)Cp*MC———CC(OMe)——NOs

3(CO)

11]. The

former complexes react with BF3

to give [Re(NO)(PPh3)Cp*(k-g1 : g2 : g1-

CCC)Re2(CO)

9][BF

4] via MeO~ abstraction followed by an unspecified rearrange-

ment.186Hydrozirconation of the phosphaalkyne complex [Pt(dppe)(g2-P———CBu5)] gave the

metallaphosphaalkene [Pt(dppe)Mg2-Bu5CH——PZrClCp2N], which proved to be a useful

precursor for the synthesis of other phosphaalkene complexes. For instance, reactionwith PPh

2Cl gave [Pt(dppe)Mg2-Bu5CH——PPh

2N] as a mixture of cis- and trans

isomers.187The terminal phosphorusmonoxide ligand in [MoMNR(R@)N3(P——O)] reacts

with [ZrMe2Cp

2] to give [CpMeZrMOP(Me)Mo[NR(R@)]

3NCp

2] via addition of

Zr—Me across the phosphoryl moiety.188The heterometallic sulfido cluster [Mo

2Co

2(CO)

4S3Cp

2] reacts with dppm and

dppe to give [Mo2Co

2(CO)

2S3LCp

2] (L\dppm or dppe) and with dmpe to give

[Mo2Co

2(k

3-CO)S

3(dmpe)

2Cp

2]. The latter reacts with dichloromethane, with loss of

a carbonyl ligand, to form the cationic methylidyne cluster [Mo2Co

2S3(k

3-

CH)(dmpe)2Cp

2]`.189 Oxidation of [Mo

2Co

2(CO)

2S4Cp*

2] gave the 58-valence shell

electron cluster [Mo2Co

2S4(X)

2Cp*

2] (X\ I, Br or Cl). Structural changes associated

with the oxidation are consistent with removal of electron density from a Co—Cop-bond. In an attempted catalytic reaction [Mo

2Co

2(CO)

2S4Cp*

2] reacts with excess

benzenethiol to give phenylthiobenzoate, PhS(CO)Ph, and PhSSPh.190 The 60-val-ence shell electron cluster [M@

2MA

2S4(NO)

2R

2] (R\CpA, Cp* or Cp; M@\Mo or W;

MA\Fe or Co) have been prepared from Mo—S cluster synthons and iron—nitrosylcomplexes as a source of the Fe—NO vertex. The redox properties and electronicstructure of these clusters have been examined.191 Sodium amalgam reduction of thecubane [Mo

2Co

2S4(CO)

2(g5-CpA)

2] gave the paramagnetic cluster anion

[Mo2Co

2S4(CO)

2(g5-CpA)

2]~. Similar clusters have been isolated from the reaction

between [Mo2Co

2S3(CO)

4(g5-CpA)

2] and p-toluenethiolate. The Co—Co distance of

2.75Å in this 61-valence shell electron cluster suggests that the additional electron isprobably located in a Co—Co p* molecular orbital.192

The reaction of [Ru3(CO)

12] with [Ga

2Cl

4] in the presence of gallium metal gave

[RuMGaCl(thf)2NMGaCl

2(thf)N

2(CO)

3]·1.5thf and [Ru

2MGaCl

2(thf)N

2(CO)

8]; the for-

mer contains a Ru—GaI bond trans to a Ru—GaII bond.193 Mixed Ti—Pt tetramericmetallamacrocycles have been self-assembled via interaction of [Ti(O

2CC

5H

4N)

2Cp

2]

with cis-[Pt(PR3)2(OSO

2CF

3)2].194 The amphiphilic organoruthenium—oxomolyb-

denum cluster [(p-Pr*C6H

4Me)

4Ru

4Mo

4O

16] has been prepared from sodium molyb-

date and (p-cymene)ruthenium dichloride dimer.195 The iron—rhodium and iron—irid-ium nitrido carbonyl clusters [Fe

5M(N)(CO)

15]2~ (M \ Rh or Ir) have been prepared

and structurally characterised and their redox properties examined.196 Addition of[AuCl(PPh

3)] and [MRhCl(CO)N

2] to [Fe

3(CO)

9(k

3-O)]2~ gave the trigonal bi-

pyramidal clusters [Fe3Au(CO)

12(PPh

3)2(k

3-O)] and [Fe

3Rh

3(CO)

15(k

3-O)]~. In

both cases the [Fe3(k

3-O)] fragment remains essentially unchanged, preferring the low

co-ordinate peripheral location.197High-temperature oxidation of [WRe

2(CO)

9(k-C———CPh)Cp*] in the presence of O

2gave [WRe

2(CO)

8(O)(k

3-C——CPh)Cp*] which reacts with H

2to afford the acetylide

cluster [WRe2(k-H)

2(CO)

6(k-O)(k

3-C———CPh)Cp*], the alkenyl cluster

[WRe2(CO)

8(O)(k

2-CH——CHPh)Cp*] and the alkylidene cluster [WRe

2(CO)

8(O)(k

2-

434 S. Doherty

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CHCH2Ph)Cp*], transformations that require the addition of two moles of H

2and

elimination of two carbonyls, and hydrogenation of the acetylide ligand and theresultant alkenyl ligand respectively. The vinylacetylide cluster [WRe

2(CO)

9(O)Mk

3-

C———C(CMe——CH2)NCp*] reacts with H

2to give similar products as well as the allenyl

cluster [WRe2(CO)

7(k-O)Mk

3-(H)C——C——CMe

2NCp*].198 Trimethylamine oxide in-

itiated condensation of [Ru5(k

5-C)(CO)

15] and [W(CO)

3(g1-C———CPh)L] (L\Cp or

Cp*) gave two heterometallic carbido alkylidyne clusters [WRu5L(k

5-C)(CO)

15(k

4-

C———CPh)] and [WRu5L(k

5-C)(CO)

13(k

4-C———CPh)]. Hydrogenation of the latter results

in 1,1-addition to the k3-acetylide and the formation of two or four hydride bridges to

give [WRu4(k-H)

2(CO)

13(k

6-C)(k

3-CCH

2Ph)Cp*] and [WRu

5(k-H)

4(CO)

12(k

4-

C)(k3-CCH

2Ph)Cp*] respectively.199 Condensation of [WRu

2(k

3-C———CPh)(CO)

8Cp*]

with excess [WH(CO)3Cp*] gave a range of clusters including [W

3Ru

2(CO)

9(k

4-

C)(k3-CPh)Cp*

3], [WRu

3(k-H)

3(CO)

11Cp*], [W

2Ru

2(CO)

9(k

3-C——CHPh)Cp*

2] and

[W2Ru

3(CO)

11(k

5-C)(O)Cp*

2], whereas [WRu

2(k

3-C———CBu5)(CO)

8Cp*] gave the

acetylide cluster [W3Ru

3(CO)

9(k

3-C———CBu5)Cp*

3] containing a k

4-CO ligand.200 The

synthesis and reactivity of a range of Os3W clusters bearing an acetylide ligand has

been investigated. Condensation of [W(CO)3(g1-C———CR)Cp*] (R\Ph, Bu/, CH

2OMe

or CH2OPh) and [Os

3(CO)

10(NCMe)

2] affords two interconvertible isomeric butter-

fly clusters of formula [WOs3(CO)

11(k

4-C———CR)Cp*]. Thermolysis of

[WOs3(CO)

11(k

4-C———CR)Cp*] (R \Ph) results in loss of CO and C—C bond cleavage

to give [WOs3(k

4-C)(CO)

10(k-CPh)Cp*] while for R\Bu/ and CH

2OMe carbonyl

loss gave the carbide—vinylidene clusters [WOs3(k-H)(k

4-C)(CO)

9(k

2-C——CHR)Cp*].

In contrast CO loss from [WOs3(CO)

11(k-C———CCH

2OPh)Cp*] gave two isomers of

the benzofuryl cluster [WOs3(k-H)

2(CO)

9(k

4-C)(k-C

8H

6O)Cp*] via orthometallation,

C—C bond formation and H-migration.201 The heterometallic cluster [WOs3(CO)

9(k-

O)2(k-C———CPh)Cp*] contains two edge-bridging oxo groups and an g2-acetylide ligand

that bridges an open metal—metal bond. Carbonylation at 800psig gave the spikedtriangular cluster [WOs

3(CO)

11(O)(k-O)(g1-C———CPh)Cp*] while hydrogenation re-

sulted in removal of the acetylide to give [WOs3(k-H)(CO)

9(k-O)

2Cp*].202 The

double-bonded oxo—metallacyclopentadiene complex [Mo2(O)(k-O)(k-C

4Ph

4)Cp

2]

reacts with [Ru3(CO)

12] to give the pentanuclear bow-tie cluster [Mo

2Ru

3(CO)

8(k

3-

O)(k3-CPh)(k

3-C

3Ph

3)Cp

2] which contains a dimetallaallyl fragment and an al-

kylidyne ligand.203 The oxo-bridged heterometallic tungsten—ruthenium complexes[Ru

4W(CO)

10(O)

2(k

4-PPh)(k

5-C———CPh)Cp*], [Ru

4W(CO)

7(O)

2(g6-C

6H

5Me)(k

4-

PPh)(k5-C———CPh)Cp*] and [Ru

5W(CO)

12(O)

2(k

4-PPh)(k

4-C———CPh)Cp*] have been

prepared by the condensation of [Ru4(CO)

13(k

3-PPh)] and [W(O)

2(g1-C———CPh)Cp*]

in toluene at reflux.204 The dinuclear oxo—acetylide [WRe(k-H)(CO)4(O)(k-C———CPh)]

reacts with alkynes to afford complexes containing substituted cyclopentadienylideneligands and folded metallocyclopentadienyl structures. For instance, reaction withDMAB affords the bis(alkylidene) complex [WRe(CO)

3(O)Cp*(k-CHPh)Mk-

C5(CO

2Me)

4N] via C—C formation and C———C cleavage reactions. In comparison, reac-

tion with di-p-tolylacetylene gave [WRe(CO)3(O)Cp*MCH(Ph)CC(C

6H

4Me-p)CH(k-

g2-C6H

3Me)N], [WRe(CO)

3(O)Cp*Mk-C

4Ph[C

2H(C

6H

4Me-p)

2](C

6H

4Me-p)

2N] and

[WRe(CO)3(O)Cp*Mk-C

4[C

2H(C

6H

4Me-p)

2]Ph(C

6H

4Me-p)

2N]. The last two com-

plexes contain folded metallacyclopentadienyl rings, formed via coupling of a cis-ditolylalkenyl intermediate with the acetylide and a second equivalent of ditolylacety-lene.205 Several new mixed-metal clusters have been isolated from the reaction be-

435Organometallic chemistry of bi- and poly-nuclear complexes

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tween [Ir(CO)Cl(PPh3)2] and Na[Ru

3H(CO)

11] and include

[Ru3IrH

3(CO)

11(PPh

3)], [Ru

3IrH(CO)

12(PPh

3)] and [Ru

4~xIr

x(CO)

10(PPh

3)2]

(x\ 1 or 2).206

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