Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 109. Reactions of tungsten–molybdenum dimetal compounds bearing carbaborane ligands with alkynes; crystal structure of [MoW(µ-C4Me4){σ,η5-CH(C6H4Me-4)C2B9H8Me2}(η-C7H7)]

Treatment of the compounds [MoW(µ-CR)(CO)2(η-C7H7)(η5-C2B9H9Me2)] in thf (tetrahydrofuran) with the alkynes MeCCMe or EtCCEt affords the complexes [MoW(µ-CR)(CO)(η-R′C2R′)(η-C7H7)(η5-C2B9H9Me2)](R = C6H4Me-4, R′= Me; R = CCBut, R′= Me or Et). Similar reactions between [MoW(µ-CC6H4Me-4)(CO)2(η-C7H7)(η5-C2B9H10Me)] and MeCCMe or PhCCPh yield the related species [MoW(µ-CC6H4Me-4)(CO)(η-R′C2R′)(η-C7H7)(η5-C2B9H10Me)](R′= Me or Ph). The reaction of [MoW(µ-CC6H4Me-4)(CO)(η-MeC2Me)(η-C7H7)(η5-C2B9H9Me2)] with MeCCMe in toluene at 100 °C gives a novel dimetal complex [MoW(µ-C4Me4){σ,η5-CH(C6H4Me-4)C2B9H8Me2}(η-C7H7)], the structure of which was established by X-ray diffraction. The Mo–W bond [2.922(1)A] is symmetrically bridged by a µ-C4Me4 fragment, the carbon atoms of which are linked to both metal atoms in the η4 fashion. The molybdenum atom carries the η-C7H7 ligand, and the tungsten atom is ligated by a CH(C6H4Me-4)C2B9H8Me2 fragment. In the latter the CH(C6H4Me-4) moiety forms a bridge between the tungsten [W–C 2.226(8)A] and a boron atom [B–C 1.54(1)A] in the pentagonal face of the cage. This boron atom is in the β site ([graphic omitted]) with respect to the carbon atoms, and all the atoms of the ring are bonded to the tungsten, but the connectivities are somewhat asymmetric [2.227(9)–2.472(9)A]. The 1H and 13C-{1H} NMR data for the new compounds are reported and discussed.