A Metallabicycle From Thiocarbonyl-Cyclopropenium Coupling.

Addition of triphenylcyclopropenium bromide to the thiocarbonyl complex [RhCl(CS)(PPh3 )2 ] affords novel bicyclic metalla-3-mercapto-thiapyrylliums [Rh(κ2 -C,S-C5 S2 Ph3 )(PPh3 )2 X2 ] (X=Cl, Br) - heterocycles with no metal-free isolobal precedent. Halide abstraction with silver triflate (AgOTf) in acetonitrile affords the salt [Rh(κ2 -C,S-C5 S2 Ph3 )(NCMe)2 (PPh3 )2 {Ag(OH2 )2 }{Ag(OTf)3 }]-OTf which in turn reacts with sodium chloride to return [Rh(κ2 -C,S-C5 S2 Ph3 )(PPh3 )2 Cl2 ].

Poly(imidazolyliden-yl)borato Complexes of Tungsten: Mapping Steric vs. Electronic Features of Facially Coordinating Ligands.

A convenient synthesis of [HB(HImMe)3](PF6)2 (ImMe = N-methylimidazolyl) is decribed. This salt serves in situ as a precursor to the tris(imidazolylidenyl)borate Li[HB(ImMe)3] pro-ligand upon deprotonation with nBuLi. Reaction with [W(≡CC6H4Me-4)(CO)2(pic)2(Br)] (pic = 4-picoline) affords the carbyne complex [W(≡CC6H4Me-4)(CO)2{HB(ImMe)3}]. Interrogation of experimental and computational data for this compound allow a ranking of familiar tripodal and facially coordinating ligands according to steric (percentage buried volume) and electronic (νCO) properties. The reaction of [W(≡CC6H4Me-4)(CO)2{HB(ImMe)3}] with [AuCl(SMe2)] affords the heterobimetallic semi-bridging carbyne complex [WAu(µ-CC6H4Me-4)(CO)2(Cl){HB(ImMe)3}].

Pnictogen-Functionalised C1 Ligands: MC-ARn (n=0, 1, 2, 3).

The chemistry of transition metal carbynes, Ln M≡CR, has historically been dominated by species bearing hydrocarbyl or amino 'R' substituents, with other elements appearing only sporadically. In recent years, carbynes and related 'C1 ' species bearing other main-group substituents, particularly heavier elements of the p-block, have begun to emerge. This review details the chemistry of heavier pnictogen-functionalised C1 ligands, MCARn (A=P, As, Sb, Bi; n=0-3), including their syntheses, properties and reactivities, and how these are distinguished from more traditional carbyne complexes. Recent developments in the closely related phospha-isonitrile Ln M(CPR), cya-phosphide and cya-arside ligands, Ln M(C≡A) (A=P, As), are also discussed.

Propargylidyne and Pentadiynylidyne Polyfunctionalised Polycyclic Aromatic Hydrocarbons.

The Pd0 /AuI mediated [C1 +C2 ] cross-coupling reactions of [W(≡CBr)(CO)2 (Tp*)] (Tp*=hydrotris(dimethylpyrazolyl)borate) and trimethylsilylethynyl-substituted arenes afford new polycyclic aromatic hydrocarbon propargylidynes [W(≡CC≡CR)(CO)2 (Tp*)] (R=9-anthracenyl, 1-pyrenyl). The strategy extends to the first bis(propargylidyne) and bis(pentadiynylidyne) complexes bridged by phenyl or anthracenyl spacers, and to a tetrakis(propargylidyne) connected through a pyrene core.

Advances in Transition Metal Seleno- and Tellurocarbonyl Chemistry.

In contrast to the ubiquity of transition-metal carbonyl, and (to a lesser extent) thiocarbonyl complexes, transition-metal complexes of carbon monoselenide Ln MCSe and monotelluride Ln MCTe remain scarce. The last few years, however, have seen notable steps towards expanding this chemistry, specifically with regards to new systematic studies on homologous sets of chalcocarbonyl complexes Ln MCE (E=O, S, Se, Te), the first reports of new bi- and polynuclear CSe and CTe bridging complexes and a confluence with metal carbido chemistry. Herein the properties, syntheses and reactions of these rare but fundamentally intriguing compounds are discussed.

In Search of Fulminate Analogues: Ln M≡CP=NR.

The "CPNR" ligand may be viewed as being isolobal with fulminate, CNO; however, attempts to prepare a complex of such a ligand resulted instead in a range of novel imino and aminophosphinocarbyne complexes. Sequential treatment of [Mo(≡CBr)(CO)2 (Tp*)] (Tp*=hydrotris(dimethylpyrazolyl)borate) with nBuLi and ClP=NMes* (Mes*=C6 H2 tBu3 -2,4,6) afforded mixtures of the complexes [Mo(≡CPnBuNHMes*)(CO)2 (Tp*)] and traces of the bimetallic products [Mo2 {µ2 -C2 P2 O(NHMes)2 }(CO)4 (Tp*)2 ] and [Mo2 (µ2 -C2 PNHMes)(CO)4 (Tp*)2 ]. The reaction of [W(≡CBr)(CO)2 (Tp*)] with nBuLi and ClP=NMes* afforded predominantly the mononuclear carbyne [W{≡CP(=NMes*)nBu2 })(CO)2 (Tp*)] and traces of the binuclear complex [W2 (µ-C2 PNHMes)(CO)4 (Tp*)2 ] which is also obtained when tBuLi is used. Although not isolable, the intended complexes [M(≡CPNMes*)(CO)2 (Tp*)] could be generated in situ and spectroscopically characterized via the reactions of the stannyl carbynes [M(≡CSnnBu3 )(CO)2 (Tp*)] and ClP=NMes*. The preceding observations are mechanistically interpreted with reference to a computational interrogation of the model complex [Mo(≡CP=NCH3 )(CO)2 (Tp*)], the LUMO of which has considerable phosphorus character.

A Dirhoda-Heterocyclic Carbene.

The linear µ-carbido complex [Rh2 (µ-C)Cl2 (dppm)2 ] (dppm=bis(diphenylphosphino)methane) reacts with dimethylacetylene dicarboxylate (DMAD) to afford [Rh2 (µ-C)(µ-DMAD)Cl2 (dppm)2 ], which features a bent RhCRh linkage (124.7°) that might be described as a dirhoda-heterocyclic carbene, as demonstrated by coordination to further metal centers.

An Approach to Carbide-Centered Cluster Complexes.

We report the first examples of the carbide ligand in (Cy3P)2Cl2Ru≡C (RuC) developing into a µ3 ligand toward metal centers. Conventionally, sterics exclude this coordination mode, but Fe2(CO)9 and Co2(CO)8 expel bridging CO ligands upon reaction with RuC to form trimetallic (Cy3P)2Cl2Ru═CFe2(CO)8 (RuCFe2) and (Cy3P)2Cl2Ru═CCo2(CO)7 (RuCCo2) complexes. Thus, the proximity offered by metal-metal associations in bimetallic carbonyl complexes allows the formation of trinuclear carbide complexes as verified by NMR, Mössbauer, and X-ray spectroscopic techniques.

Dimetallapoly-yn-diylidynes: Ln M≡C-(C≡C)x -C≡MLn (x=0-4).

Synthetic routes to dimetallated Cx carbon wires in which two metals are separated by a linear carbon chain involving terminal metal-carbon triple bonds are described for the complexes [(Tp*)(CO)2 W≡C-(C≡C)n -C≡W(CO)2 (Tp*)] (Tp*=hydrotris(dimethylpyrazolyl)borate) where n=1, 3 or 4, joining the previously known examples with n=0, 1 and 2 to complete the series as models for linear carbyne C∞ .

Flexible Platinum(0) Coordination to a Ditungsten Ethanediylidyne.

The lithiocarbyne [W(≡CLi)(CO)2 (Tp*)] (Tp*=hydrotris(3,5-dimethylpyrazol-1-yl)borate) reacts with [PtCl2 (L2 )] (L2 =1,5-cyclo-octadiene, norbornadiene) to furnish ditungsten ethanediylidyne complexes, [W2 {µ-C2 Pt(L2 )}(CO)4 (Tp*)2 ], wherein a trigonal platinum(0) center unsymmetrically ligates one W≡C bond in the solid state but rapidly shimmies between the two W≡C bonds in solution. The η4 -dienes are displaced by monodentate CO or isocyanide ligands to provide derivatives where both W≡C bonds coordinate to a single Pt0 center, attended by significant distortion of the WCCW spine.

Pentadiynylidyne and Pentacarbido Complexes.

The reaction of the halocarbyne [W(≡CBr)(CO)2 (Tp*)] (Tp*=hydrotris(3,5-dimethylpyrazol-1-yl)borate) with trimethylsilyl-butadiyne, mediated by [Pd(PPh3 )4 ] and CuI, affords the first pentadiynylidyne complex [W(≡CC≡CC≡CSiMe3 )(CO)2 (Tp*)]. Desilylation provides a general route to heterobimetallic pentacarbido complexes, including [(Tp*)(CO)2 W(µ-C5 )(PPh3 )2 Ru(η-C5 H5 )] and [(Ph3 P)2 (CO)HIr{(µ-C5 )W(CO)2 (Tp*)}2 ].

Bi- and Polynuclear Transition-Metal Carbon Tellurides.

The first examples of bi- and polynuclear tellurocarbonyl complexes were obtained from the reactions of [W(≡CTe)(CO)2 (Tp*)]NEt4 (Tp*=hydrotris(dimethylpyrazolyl)borate) with [MCl(PCy3 )]/TlPF6 (M=Cu, Au) or [Au2 Cl2 (µ-dppm)], which afford [WM(µ-CTe)(PCy3 )(CO)2 (Tp*)] (M=Cu, Au) and [WAu2 (µ-CTe)(µ-dppm)(CO)2 (Tp*)]3 (PF6 )3 . In all cases it is specifically the tellurocarbonyl that assumes a bridging, but in each case distinct, role including examples of isotellurocarbonyl, semi-bridging and σ-π coordination and combinations thereof. Tetrametallic complexes bridged by C2 Te and C2 Te2 ligands are also described.

Secondary phosphinocarbyne and phosphaisonitrile complexes.

The palladium-mediated reaction of [W(≡CBr)(CO)2(Tp*)] (Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate) with primary phosphines PH2R (R = Ph, Cy) affords the secondary phosphinocarbyne complexes [W(≡CPHR)(CO)2(Tp*)], deprotonation of which provides the anionic phosphaisonitrile complexes [W(CPR)(CO)2(Tp*)](-), including the structurally characterized salt [W(CPPh)(CO)2(Tp*)][K(kryptofix)].

σ-Arsolido complexes.

The σ-stannyl complexes [M(SnnBu3)(CO)n(η5-C5H5)] (n = 3, M = Mo, W; n = 2, M = Fe) serve as mild reagents for the installation of σ-arsolyl ligands in transmetallation reactions with As-chloro-arsoles ClAsC4R4 (R = Me, Ph) to afford [M(σ-AsC4R4)(CO)n(η5-C5H5)]. The reaction of [Cr(SnnBu3)(CO)3(η5-C5H5)] with ClAsC4Ph4 most likely proceeds in a similar manner but is immediately followed by rapid formation of (AsC4Ph4)2 and [Cr2(CO)6(η5-C5H5)2]. The reaction of [Mo(SnnBu3)(CO)3(η5-C5H5)] with ClAsC4(SiMe3)-2,5-Me2-3,4 is accompanied by monodesilylation to afford [Mo{σ-AsC4(SiMe3)-2-Me2-3,4}(CO)3(η5-C5H5)]. The slow reaction of [Fe(SnnBu3)(CO)2(η5-C5H5)] with ClAsC4Me4 produced only traces of [Fe(σ-AsC4Me4)(CO)2(η5-C5H5)] due to competition with the Diels-Alder type dimerisation of the haloarsole. Although attempts to decarbonylate the σ-arsolyl complexes were unsuccessful, computational analysis suggests that the trigonal 'XL' arsolenium coordination mode is viable.

Electrophilic As-functionalisation of σ-arsolido complexes.

The σ-arsolido complex [Mo(AsC4Me4)(CO)3(η5-C5H5)] is alkylated at arsenic by MeOTf to afford the pentamethylarsole complex [Mo(MeAsC4Me4)(CO)3(η5-C5H5)](OTf) while iodomethane affords a mixture of [Me2AsC4Me4]I, [MoMe(CO)3(η5-C5H5)], [MoI(CO)3(η5-C5H5)] and the arsole complexes cisoid- and transoid-[MoI(MeAsC4Me4)(CO)2(η5-C5H5)] and transoid-[Mo{C(O)Me}(MeAsC4Me4)(CO)2(η5-C5H5)], The arsole ligand in [Mo(MeAsC4Me4)(CO)3(η5-C5H5)](OTf) is readily liberated by NaI in acetone to afford free MeAsC4Me4 and [MoI(CO)3(η5-C5H5)]. In a similar manner, the reaction of [Mo(AsC4Ph4)(CO)3(η5-C5H5)] with MeI affords MeAsC4Ph4 and [MoI(CO)3(η5-C5H5)], while [Mo{AsC4(SiMe3)-2-Me2-3,4}(CO)3(η5-C5H5)] with MeOTf affords [Mo{MeAsC4(SiMe3)-2-Me2-3,4}(CO)3(η5-C5H5)](OTf). The reaction of [Mo(AsC4Me4)(CO)3(η5-C5H5)] with activated alkynes (RCCR: R = CF3, CO2Me) does not proceed via [4 + 2] cyclo-addition but rather electrophilic attack at arsenic followed by metallacyclisation with incorporation of a carbonyl ligand in the spirocyclic complexes [Mo{As(C4Me4)CRCRCO}(CO)2(η5-C5H5)].

Carbon-chalcogen wires: alkynyltellurolatocarbynes.

The reactions of [W(CBr)(CO)2(Tp*)] (Tp* = tris(dimethylpyrazolyl)borate) with LiTeCCR (R = SiMe3, SiiPr3, iPr, nBu, tBu, Ph, C6H4Me-4, methylimidazol-2-yl) afford the first alkynyltellurolatocarbynes [W(CTeCCR)(CO)2(Tp*)]. Both the WC and CC multiple bonds are prone to metal addition as exemplified by treatment with [MCl(SMe2)] (M = Cu, Au) to afford the hexametallic complex [W2Cu4(µ-CTeCCSiiPr3)2Cl4(CO)4(Tp*)2] and [WAu(µ-CTeCCSiMe3)Cl(CO)2-(Tp*)] which evolves to the unusual hypervalent [WAu(µ-CTeCl4)(SMe2)(CO)2(Tp*)].

Stable cyclopropenylvinyl ligands via insertion into a transient cyclopropenyl metal bond.

Treatment of the rhodium pincer complexes [RhCl(RPm)] (RPm = N,N'-bis(di-R-phosphinomethyl)perimidinylidene, R = Ph, Cy) with triphenylcyclopropenium hexafluorophosphate affords rhodacyclobutadiene complexes. These in turn react with activated alkynes (RCCCO2Me, R = H, CO2Me) to afford unusually stable cyclopropenylvinyls, implicating the intermediacy of σ-cyclopropenyl isomers. In contrast, treatment of [RhCl{py(NHPtBu2)2-2,6}] with the same reagent instead results in double functionalisation (SEAr) at the pincer backbone.

Spodium bonding in bis(alkynyl)mecurials.

The new bis(alkynyl)mercurial Hg{CCSeCW(CO)2(Tp*)}2 (Tp* = tris(dimethylpyrazolyl)borate) forms adducts with fluoride and phenathroline, the structures of which are interpreted in the context of two-coordinate mercury presenting a σ-torroid for spodium bonding.

A golden ring: molecular gold carbido complexes.

Stannylcarbynes [M(≡CSnMe3)(CO)2(Tp*)] [M = Mo, W; Tp* = hydrotris(dimethylpyrazol-1-yl)borate], which are readily obtained via the successive treatment of [M(≡CBr)(CO)2(Tp*)] with (n)BuLi and ClSnMe3, serve as effective carbyne transmetalation agents for the preparation of heteronuclear molecular gold carbido complexes such as [M(≡CAuPPh3)(CO)2(Tp*)] and the tetrameric golden ring complex [W(≡CAu)(CO)2(Tp*)]4, which are in turn able to transfer the carbido unit to palladium.

C-H activation in bimetallic rhodium complexes to afford N-heterocyclic carbene pincer complexes.

The pro-ligands 1,8-bis(di-R-phosphinomethyl)-2,3-dihydroperimidine (RH2Pm, R = phenyl, cyclohexyl) react with [RhCl(CE)(PPh3)2] (E = O, S) to afford the bimetallic complexes [RhCl(CE)(µ-RH2Pm)]2 (E = O, S). Upon heating, these species undergo double C-H activation to afford the N-heterocyclic carbene (NHC) pincer complexes [RhCl(RPm)]. Reduction of [RhCl(CO)(µ-PhH2Pm)]2 with KC8 results in the bimetallic rhodium(0) complex, [Rh(µ-CO)(PhH2Pm)]2, with a formal Rh-Rh bond and a hydrogen-bonding interaction between rhodium and the central methylene group (C-H⋯Rh = 2.802 Å). Upon treatment with tritylium, ferrocenium or triphenylcyclopropenium tetrafluoroborates this species undergoes double C-H activation to afford a mononuclear NHC pincer complex salt, [Rh(CO)(PhPm)]BF4. Treatment of [RhCl(CO)(PhH2Pm)]2 with lithium (trimethylsilyl)acetylide provides another bimetallic species, [Rh(CCSiMe3)(CO)(PhH2Pm)]2, however heating this species does not proceed cleanly to the monomeric NHC complex, [Rh(CCSiMe3)(CO)(PhPm)] which may however be obtained from [RhCl(RPm)] and LiCCSiMe3.