Alkylidyne(carbaborane) complexes of the Group 6 metals. Part 8. Proton-induced alkylidyne ligand coupling at dimetal centres

Abstract

Protonation (HBF₄·Et₂O) of equimolar mixtures of the compounds [M(CC₆H₄Me-4)(CO)₂(η-C₅H₅)](M = Mo or W) and [NEt₄][W(CCCBu^t)(CO)₂(η⁵-7,8-C₂B₉H₁₁)] in CH₂Cl₂ at –78 °C affords the dimetal complexes [MW{µ-η³ : η²-C(Bu^t)CC[C(H)C₆H₄Me-4]}(CO)₄(η⁵-7,8-C₂B₉H₁₁)(η-C₅H₅)]. The ditungsten compounds was also obtained by protonating equimolar mixtures of [W(CCCBu^t)(CO)₂(η-C₅H₅)] and [NEt₄][W(CC₆H₄Me-4)(CO)₂(η⁵-7,8-C₂B₉H₁₁)], and the species [W₂{µ-η³ : η²-C(Bu^t)CC[C(H)C₆H₄Me-4]}(CO)₄(η⁵-7,9-C₂B₉H₁₁)(η-C₅H₅)] was similarly prepared by treating equimolar mixtures of [W(CC₆H₄Me-4)(CO)₂(η-C₅H₅)] and [NEt₄][W(CCCBu^t)(CO)₂(η⁵-7,9-C₂B₉H₁₁)] with HBF₄·Et₂O. The structure of [MoW{µ-η³ : η²-C(Bu^t)CC[C(H)C₆H₄Me-4]}(CO)₄(η⁵-7,8-C₂B₉H₁₁)(η-C₅H₅)] has been established by X-ray diffraction. The Mo–W bond [3.031(2)Å] is bridged by a C(Bu^t)CC[C(H)C₆H₄Me-4] unit [average C–C 1.40(3)Å]. All three carbon atoms of the chain ligate the Mo atom but only two carbons of the C(Bu^t)CC fragment ligate the W atom. The latter is also co-ordinated by the nido-icosahedral 7,8-C₂B₉H₁₁ cage and two CO groups, and the Mo atom is co-ordinated by a C₅H₅ ring and two CO ligands, as expected. Solutions of the compounds [MW{µ-η³ : η²-C(Bu^t)CC[C(H)C₆H₄Me-4]}(CO)₄(η⁵-7,8- or -7,9-C₂B₉H₁₁)(η-C₅H₅)] slowly (days) convert into new species of formulation [MW{µ-η³ : η²,η⁵-C(H)(C₆H₄Me-4)CC[C(H)(Bu^t)(7,8- or 7,9-C₂B₉H₁₀)]}(CO)₄(η-C₅H₅)], a process accelerated by refluxing in tetrahydrofuran. The ¹H and ¹³C{¹H} NMR data of the new compounds are reported and discussed in relation to the structures proposed.