Tethered Alkylidenes for REMP from Carbon Disulfide Cleavage

Reactions between tungsten alkylidyne [tBuOCO]W≡CtBu(THF)2 1 and sulfur containing small molecules are reported. Complex 1 reacts with CS2 to produce intermediate η2 bound CS2 complex [O2C(tBuC═)W(η2-(S,C)-CS2)(THF)] 8. Heating complex 8 provides a mixture of a monomeric tungsten sulfido complex 9 and a dimeric complex 10 in a 4:1 ratio, respectively. Heating the mixture does not perturb the ratio. Addition of excess THF in a solution of 9 and 10 (4:1) converts 10 to 9 (>96%) with concomitant loss of (CS)x. Both 9 and 10 can be selectively crystallized from the mixture. An alternative synthesis of exclusively monomeric 9 involves the reaction between 1 and PhNCS. Demonstrating ring expansion metathesis polymerization (REMP), tethered tungsten alkylidene 8 polymerizes norbornene to produce cis-selective syndiotactic cyclic polynorbornene (c-poly(NBE)).

Inorganometallic allenes [(Mn(η5-C5H5)(CO)2)2(μ-E)] (E = Si-Pb): bis-allylic anionic delocalisation similar to organometallic allene but differential σ-donation and π-backdonation

The chemistry of heavy group-14 tetrel atoms is known to diverge from that of the lighter congener carbon. Here, we report the structure and bonding in inorganometallic allenes [(MnCp(CO)2)2(μ-E)] (2E, E = Si-Pb; Cp = η5-C5H5). These inorganometallic allenes are structurally similar to the lighter organometallic analog [(MnCp(CO)2)2(μ-C)] (2C). The bonding analysis of these compounds at the M06/def2-TZVPP//BP86/def2-SVP level of theory identifies a linear Mn-E-Mn spine with delocalised, mutually orthogonal π-systems across this back-bone. This results in a bis-allylic anionic bonding scenario. However, the strength of the Mn-E bonding is found to be weaker in these inorganometallic allenes. The energy decomposition analysis at the BP86/TZ2P//BP86/def2-SVP level of theory further reveals that the bonding in these compounds cannot be represented by one unique heuristic bonding model, but multiple bonding models. For all 2E (E = C-Pb), the Dewar-Chatt-Duncanson bonding model is one of the best bonding representations, where the central tetrel atom acts as a 4e- σ-donor and 4e- π-acceptor. The bonding analysis indicates that the carbon atom in the organometallic allene acts as a better π-acceptor than σ-donor, while the heavier tetrel atoms in the inorganometallic allenes are better σ-donors than π-acceptors. The npz-orbital is found to be a better σ-donor than the valence ns-orbital. However, when the bonding representation is changed to a traditional electron-sharing model, the contribution from the ns-orbital was found to be the largest in comparison to the interaction from the remaining three valence np-orbitals. It can be suggested that the ns-orbitals contribute more towards chemical bonding when participating via an electron-sharing interaction than a donor-acceptor interaction.

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.

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.

A heterobimetallic cumulenic μ-carbido complex

Cleavage of a selenocarbonyl ligand in [W(CSe)(NO)(CO)(Tp*)] by [Re(THF)(CO)₂(Cp)] provides heterobimetallic cumulenic μ-carbido and μ-selenido 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.

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.

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.

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.

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.