Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 99. Synthesis of the cluster compounds [MWCoAu(µ-CC6H4Me-4)(µ3-CR)(CO)4(η-C5H5)(η-C5Me5)(η5-C2B9H9Me2)](M = Mo or W, R = C6H4Me-4; M = W, R = Me); crystal structure of the complex [MoWCoAu-(µ-CC6H4Me-4)(µ3-CC6H4Me-4)(CO)4(η-C5H5)(η-C5Me5)(η5-C2B9H9Me2)]·CH2Cl2

Abstract

The trimetal complexes [MWAu(µ-CC₆H₄Me-4)₂(CO)₄(η-C₅H₅)(η⁵-C₂B₉H₉Me₂)](M = Mo or W), with molecular structures based on a MAuW spine and each metal–metal bond bridged by a p-tolylmethylidyne group, react with [Co(η-C₂H₄)₂(η-C₅Me₅)] in CH₂Cl₂ at room temperature to afford the tetranuclear metal compounds [MWCoAu(µ-CC₆H₄Me-4)(µ₃CC₆H₄Me-4)(CO)₄(η-C₅H₅)(η-C₅Me₅)(η⁵-C₂B₉H₉Me₂)]. An X-ray diffraction study on the molybdenum-containing product revealed a structure with the Co(η-C₅Me₅) fragment co-ordinated to the 4-MeC₆H₄C = W(CO)₂(η⁵-C₂B₉H₉Me₂) group of the precursor. The cobalt atom is also bonded to the gold, so the metal core consists of a WCoAu triangle [W–Co 2.597(2), W–Au 2.826(1), and Co–Au 2.580(2)Å] spiked by the molybdenum [Mo–Au 2.763(2)Å]. The p-tolylmethylidyne ligands asymmetrically bridge the metal sites. One group spans the Mo–Au bond [µ-C–Au 2.11(1) and µ-C–Mo 1.90(2)Å], and the other the WCoAu triangle [µ-C–Au 2.30(1), µ-C–Co 1.86(1), and µ-C–W 1.97(1)Å]. The Mo, W, and Co atoms are co-ordinated by the η-C₅H₅, η⁵-C₂B₉H₉Me₂, and η-C₅Me₅ groups, respectively. The Mo and W atoms each carry two CO ligands, but one of these attached to tungsten semi-bridges the W–Co bond [W–C–O 163(1)°]. The reaction between [Co(η-C₂H₄)₂(η-C₅Me₅)]and[W₂Au(µ-CMe)(µ-CC₆H₄Me-4)(CO)₄(η-C₅H₅)(η⁵-C₂B₉H₉Me₂)] affords a mixture of two isomeric products. Their structures correspond to the alternative possibilities of addition of a Co(η-C₅Me₅) fragment to either the MeC = W(CO)₂(η⁵-C₂B₉H₉Me₂) or the 4-MeC₆H₄C = W(CO)₂(η-C₅H₅) group in the precursor, but the former isomer predominates. The spectroscopic (i.r. and n.m.r.) properties of the new compounds are reported and discussed.