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}].

Synthesis and reactivity of 9,10-bis(4-trimethylsilylethynylbuta-1,3-diynyl)anthracene derived chromophores

9,10-Bis(4-trimethylsilylethynylbutadiynyl)anthracene is readily availabe from the reaction of anthraquinone and LiCCCCSiMe₃ followed by reduction with Sn(II) and serves as a convenient building block via desilylation and palladium-mediated C-C coupling processes for the construction of further butadiynylanthracenes terminated by metal complexes, arenes, haloarenes and alkynyl functionalities.

Vanadium complexes with N-heterocyclic vinylidene ligands

The preparation and the structural characterization of vanadium complexes with terminal and bridging N-heterocyclic vinylidene ligands is reported. The synthesis of the complexes was enabled by utilization of diazoolefins as ligand precursors. Structural data and theoretical results show that N-heterocyclic vinylidenes can act as 6e^- donor ligands, leading to strong metal-carbon interactions.

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.

Symmetric and non-symmetric anthracen-diyl bis(alkylidynes)

Three examples of 9-bromo-10-(alkylidynyl)anthracenes, [W{CC(C₆H₄)₂CBr}(CO)₂(L)] (L = hydrotris(dimethylpyrazol-1-yl)borate Tp*, hydrotris(pyrazol-1-yl)borate Tp, hydrotris(2-mercapto-N-methylimidazol-1-yl)borate Tm) were prepared via modified Fischer-Mayr acyl oxide-abstraction protocols. With a sufficiently bulky ancillary ligand (L = Tp*) the aryl bromide is ammenable to cross-coupling reactions that enable more elaborate derivatives to be prepared. These including symmetric bis(alkylidynyl)anthracenes as well as non-palindromic examples bearing disparate metals and/or co-ligands. In contrast, these couplings fail for smaller ligands (L = Tp, Tm) where it was found that Pd⁰ or Pt⁰ were instead able to coordinate across two WC bonds to give trimetallic bow-tie complexes, [W₂M{μ-CC(C₆H₄)₂CBr}₂(CO)₄(L)₂] (M = Pd, Pt; L = Tp, Tm).

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.

Bi- and poly(carbyne) functionalised polycyclic aromatics

The Pd⁰/Au^I-mediated coupling between a tungsten stannylcarbyne and a diverse range of aryl halides has allowed from one to four carbynes to be appended to, and bridged by, central aromatic ring systems including fused polycyclic examples.

Metal coordination to bipyridyl carbynes

A new synthetic approach to hetero-aryl substituted carbyne complexes has allowed the synthesis of bipyridyl functionalised carbynes and bis(carbynes) with three potential sites for metal coordination to either the two pyridyl donors or the WC bond.

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.

Carbyne decorated porphyrins

Porphyrins peripherally decorated with four transition-metal carbynes substituents are obtained in one step via a Pd⁰/Au^I transmetallation shuttle beginning with a stannyl carbyne.

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.