Heterodinuclear Bridging Carbido and Phosphoniocarbyne Complexes

Isonitrile μ2-carbido complexes

The μ-carbido complex [WPt(μ-C)Br(CO)2(PPh3)2(Tp*)] (Tp = hydrotris(dimethylpyrazolyl)borate) undergoes substitution of one phosphine ligand with isonitriles to afford complexes [WPt(μ-C)Br(CNR)(CO)2(PPh3)(Tp*)] (R = tBu, C6H3Me2-2,6, C6H2Me3-2,4,6). For aryl but not alkyl isocyanides disubstitution follows to afford [WPt(μ-C)Br(CNR)2(CO)2(Tp*)] (R = C6H2Me2-2,6, C6H2Me3-2,4,6). The bis(isonitrile) derivatives, including [WPt(μ-C)Br(CNtBu)2(CO)2(Tp*)], may also be prepared from the reactions of triangulo-[Pt3(CNR)6] with [W(CBr)(CO)2(Tp*)]. Bis- and tris(dimethylpyrazolyl)borate pro-ligand salts replace the bromide and one phosphine in [WPt(μ-C)Br(CNC6H2Me3)(CO)2(PPh3)(Tp*)] or the bromide and one isonitrile in [WPt(μ-C)Br(CNC6H2Me3)2(CO)2(Tp*)] to afford [WPt(μ-C)(CNC6H2Me3)(CO)2(Tp*)(L)] (L = κ2-Tp*, dihydrobis(pyrazolyl)borate). Structural, spectroscopic and computational data for the complexes are discussed to interrogate the nature of the WC-Pt carbido bridge by analogy with a range of other sp-C1 and sp-B1 ligands (CN, CCH, CP, CAs, CSb, CNO, BO, BNH and BCH2).

Arsinocarbyne reactivity

The reactivity of the tungsten diphenylarsinocarbyne [W(CAsPh₂)(CO)₂(Tp*)] (1; Tp* = hydrotris(dimethylpyrazolyl)borato) is described. The pyramidal arsenic coordinates to a selection of 5d metal centres, forming heterobi- or trimetallic complexes with osmium(II), iridium(III), platinum(II) and gold(I). In the latter case, the WC bond provides a competitive site for gold(I) coordination. Treatment with MeOSO₂CF₃ results in methylation at arsenic to give the first example of an arsoniocarbyne, [W(CAsPh₂CH₃)(CO)₂(Tp*)]O₃SCF₃, for which only the WC bond remains available for gold(I) coordination.

Heterobimetallic μ2-Halocarbyne complexes

The halocarbyne complexes [M(≡CX)(CO)2(Tp*)] (M = Mo, W; X = Cl, Br; Tp* = hydrotris(dimethylpyrazolyl)borate) react with [AuCl(SMe2)], [Pt(-H2C=CH2)(PPh3)2] or [Pt(nbe)3] (nbe = norbornene) to furnish rare examples of μ2-halocarbyne...

Transition Metal Carbide Complexes

Carbide complexes remain a rare class of molecules. Their paucity does not reflect exceptional instability but is rather due to the generally narrow scope of synthetic procedures for constructing carbide complexes. The preparation of carbide complexes typically revolves around generating L_nM-CE_x fragments, followed by cleavage of the C-E bonds of the coordinated carbon-based ligands (the alternative being direct C atom transfer). Prime examples involve deoxygenation of carbonyl ligands and deprotonation of methyl ligands, but several other p-block fragments can be cleaved off to afford carbide ligands. This Review outlines synthetic strategies toward terminal carbide complexes, bridging carbide complexes, as well as carbide-carbonyl cluster complexes. It then surveys the reactivity of carbide complexes, covering stoichiometric reactions where the carbide ligands act as C₁ reagents, engage in cross-coupling reactions, and enact Fischer-Tropsch-like chemistry; in addition, we discuss carbide complexes in the context of catalysis. Finally, we examine spectroscopic features of carbide complexes, which helps to establish the presence of the carbide functionality and address its electronic structure.

Heterocyclic arsinocarbynes via tandem transmetallation

Gold(i)-catalysed tandem transmetallation (Sn→Au→As) of the stannylcarbyne [W(≡CSnⁿBu₃)(CO)₂(Tp*)] (Tp* = hydrotris-(dimethylpyrazolyl)borate) with haloarsines gives direct access to a range of novel arsinocarbyne complexes, L_nM≡CAsR₂, including unusual heterocyclic phenarsazininyl and arsolyl examples.

Construction of an iminoketenylidene

The new isonitrile-μ-carbido complexes [WPt(μ-C)Br(CNR)(PPh₃)(CO)₂(Tp*)] (R = C₆H₂Me₃-2,4,6, C₆H₃Me₂-2,6; Tp* = hydrotris(dimethylpyrazolyl)borate) rearrange irreversibly in polar solvents to provide the first examples of iminoketenylidene (CCNR) complexes.

Benzyne addition to a metal-carbon multiple bond

The linear μ-carbido complex [Rh2(μ-C)Cl2(dppm)2] (dppm = bis(diphenylphosphino)methane) reacts with a benzyne equivalent (Me3SiC6H4OTf-2/F-) to afford [Rh2(μ-CC6H4)(μ-Cl)(C6H5)Cl2(μ-dppm)2], in which the benzyne moiety adds across one of the two metal-carbon double bonds.

Carbones and Carbon Atom as Ligands in Transition Metal Complexes

This review summarizes experimental and theoretical studies of transition metal complexes with two types of novel metal-carbon bonds. One type features complexes with carbones CL₂ as ligands, where the carbon(0) atom has two electron lone pairs which engage in double (σ and π) donation to the metal atom [M]⇇CL₂. The second part of this review reports complexes which have a neutral carbon atom C as ligand. Carbido complexes with naked carbon atoms may be considered as endpoint of the series [M]-CR₃ → [M]-CR₂ → [M]-CR → [M]-C. This review includes some work on uranium and cerium complexes, but it does not present a complete coverage of actinide and lanthanide complexes with carbone or carbide ligands.

Heterobimetallic μ2-carbido complexes of platinum and tungsten

The tungsten–platinum μ-carbido complex [WPt(μ-C)Br(CO)₂(PPh₃)₂(Tp*)] (Tp* = hydrotris(dimethylpyrazol-1-yl)borate) undergoes facile substitution of both bromide and phosphine ligands to afford a diverse library of μ-carbido complexes.

Dimetalla-heterocyclic carbenes: the interconversion of chalcocarbonyl and carbido ligands

Different classes of dirhodium μ-carbido complexes cleave CS₂ to afford mono- and bi-nuclear CS complexes, the CSe analogues of which are also described.

Metal coordination of phosphoniocarbynes

Heterobi- and tetrametallic phosphoniocarbyne bridged complexes arise from the reactions of the terminal phosphoniocarbyne [W(CPMe₂Ph)(CO)₂(Tp*)]PF₆ with unsaturated metal centres.

The significance of phosphoniocarbynes in halocarbyne cross-coupling reactions

Competent intermediates as well as productive and non-productive tangents have been identified in the catalytic cycle for palladium(0)–copper(i) mediated synthesis of propargylidynes via cross coupling reactions of bromocarbyne complexes with alkynes.

Halogenation of A-frame μ-carbido complexes: a diamagnetic rhodium(ii) carbido complex

Chlorination of the new μ-carbido [Rh₂(μ-C)Cl₂(μ-dppf)₂] (dppf = 1,1′-bis(diphenylphosphino)ferrocene) affords the dirhodium(ii) complex [Rh₂(μ-C)Cl₄(μ-dppf)₂] the carbido bridge of which can only be adequately described by delocalised bonding.

Halogenation of A-frame μ-carbido complexes: synthesis of μ2-halocarbynes

The new A-frame μ₂-carbido complexes [Rh₂(μ₂-C)X₂(μ₂-dppm)₂] (X = Cl, Br; dppm = Ph₂PCH₂PPh₂) react with PhICl₂ or [pyH][Br₃] to provide rare examples of μ₂-halocarbyne complexes [Rh₂(μ-CX)(μ-X)X₄(μ-dppm)₂] (X = Cl, Br).

Tungsten–platinum μ-carbido and μ-methylidyne complexes

The lithiocarbyne [W]CLi ([W] = W(CO)₂(Tp*); Tp* = tris(dimethylpyrazolyl)borate) with divalent platinum complexes afford access to μ-carbido, μ-methylidyne and carbyne-based metallo-ligand complexes.

Platinum(ii) as an assembly point for carbide and nitride ligands

The sequential treatment of (Cy₃P)₂Cl₂RuC with [PtCl₂(C₂H₄)]₂ and (dbm)₂CrN affords a platinum(ii) center coordinated by both carbide and nitride ligands.

A [C1 + C2] route to propargylidyne complexes

The reactions of [W(CBr)(CO)₂(Tp*)] with a range of terminal alkynes (RCCH), mediated by [Pd(PPh₃)₄] and CuI, afford new propargylidynes [W(C–CCR)(CO)₂(Tp*)] [R = ^tBu, C₆H₄X (X = H, NH₂, NO₂), APh₃ (A = C, Si, Ge), B(O₂CCH₂)₂NMe].

Confluence of disparate carbido chemistries: [WRuAu2(μ-C)2Cl2(CO)2(PCy3)2(Tp*)]

The reaction of [Ru(CAuCl)Cl₂(PCy₃)₂] with [W(CSnⁿBu₃)(CO)₂(Tp*)] (obtained from [W(CBr)(CO)₂(Tp*)], ⁿBuLi and ClSnⁿBu₃) affords the heterotetrametallic bis(carbido) complex [WRuAu₂(μ-C)₂Cl₃(CO)₂(PCy₃)₂(Tp*)] in which the two distinct μ-carbido ligands adopt linear and T-shaped geometry at carbon.

A complete set of pnictocarbynes: [M(CAPh2)(CO)2(Tp*)] (M = Mo, W; A = N, P, As, Sb, Bi; Tp* = hydrotris(dimethylpyrazolyl)-borate)

The first two complete series of pnictogen functionalised carbyne complexes, [M(CAPh₂)(CO)₂(Tp*)] (M = Mo, W; A = N, P, As, Sb, Bi; Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate), have been prepared.

Simple generation of a dirhodium μ-carbido complex via thiocarbonyl reduction

The reaction of [RhCl(CS)(PPh₃)₂] with excess catecholborane affords the cumulenic carbido complex [Rh₂(μ-C)Cl₂(PPh₃)₄] which undergoes phosphine and halide substitution to afford a range of complexes in which the RhCRh spine remains intact.

Alkynylbis(alkylidynyl)phosphines: {LnMC}2PCCR

Synthetic strategies are presented for the formation of alkynylbis(alkylidynyl)phosphines which represent promising building blocks for unsaturated 2- and 3-dimensional assemblies. Parent ethynyl derivatives provide a means for installing further donor functionalities, e.g., AsPh₂ as shown.

Bis(alkylidynyl)arsines

The synthesis and characterization of the first examples of bimetallic bis(alkylidynyl)arsines are described. For the tungsten complexes, these may be prepared by a potentially generalizable route: successive treatment of [W(CBr)(CO)₂(Tp*)] with ⁿBuLi, ACl₃ (A = P, As) and a nucleophilic source of R⁻via the inferred intermediacy of [ClA{CW(CO)₂(Tp*)}₂].

Synthons for carbide complex chemistry

Harnessing lability, the miniaturized ligand sphere in a [RuC–Pt] complex establishes a straightforward building-block approach to carbide complexes.

High oxidation state bromocarbyne complexes

Bromination of the carbyne complexes [W(CR)Br(CO)₂(dcpe)] (R = Ph, SiPh₃; dcpe = 1,2-bis(dicyclohexylphosphino)ethane) provides high oxidation state derivatives [W(CPh)Br₃(dcpe)] and [W(CBr)Br₃(dcpe)], the latter via an unprecedented bromodesilylation process.

Dual nucleophilic substitution at a W(ii) η(2)-coordinated diiodo acetylene leading to an amidinium carbyne complex

The synthesis and reactivity of a W(ii) C2I2 complex towards various nucleophiles are described. Soft, aprotic nucleophiles like 4-dimethylaminopyridine (DMAP) lead to substitution of one CO at tungsten, whereas reaction with an excess of benzylamine results in a dual nucleophilic substitution at the alkyne moiety involving the rearrangement to a novel cationic amidinium carbyne complex.

Delivering carbide ligands to sulfide-rich clusters

The propensity of the terminal ruthenium carbide Ru(C)Cl₂(PCy₃)₂ (RuC) to form carbide bridges to electron-rich transition metals enables synthetic routes to metal clusters with coexisting carbide and sulfide ligands.

Carbide complexes as π-acceptor ligands

A terminal carbide complex binds as a π-acceptor towards electron-rich metal centers, mirroring CO, and provides the first homoleptic, carbide-ligated complex.

The π-accepting character of a terminal carbide complex acting as a ligand is demonstrated experimentally and corroborates earlier theoretical predictions. As a result, coordination of a terminal ruthenium carbide complex to electron-rich metal centres is shown to provide a facile and versatile route to carbide-bridged heterometallic complexes. Synthesis, reactivity, spectroscopic and structural characterization are reported for heterobimetallic systems with auxiliary metals from groups 9–11: Rh(i), Ir(i), Pd(ii), Pt(ii), Ag(i), and Au(i) coordinated by [Ru(C)Cl₂(PCy₃)₂] (RuC). This encompasses the first example of a homoleptic carbide-ligated transition metal complex: [{(Cy₃P)₂Cl₂RuC}₂Au]⁺. Kinetics of substitution on Pt(ii) by RuC ranks the carbide complex as having intermediate nucleophilicity. The ¹³C-NMR signals from the carbide ligands are significantly more shielded in the bridged heterobimetallic complexes than in the parent terminal carbide complex. Structurally, RuC forms very shorts bonds to the heterometals, which supports the notion of the multiple bonded complex acting as a π-backbonding ligand. Reactions are reported where RuC displaces CO coordinated to Rh(i) and Ir(i). A strong trans influence exerted by RuC indicates it to be a stronger σ-donor than CO. The geometries around the carbide bridges resemble those in complexes of electron-rich metals with carbonyl or bridging nitride-complex-derived ligands, which establishes a link to other strong π-acceptor ligands.