Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 75. Reactions of octacarbonyldicobalt with the salts [X][W(CR)(CO)2(η5-C2B9H9Me2)](X = NEt4 or PPh4; R = Me, Ph, C6H4Me-2, or C6H4Me-4); crystal structure of [PPh4][Co2W(µ3-CPh)(CO)8(η5-C2B9H9Me2)]·0.5CH2Cl2

In CH2Cl2, at room temperature, the salt [NEt4][W(CMe)(CO)2(η5-C2B9H9Me2)] reacts with [Co2(CO)8] to give the trimetal complex [NEt4][Co2W(µ3-CMe)(CO)8(η5-C2B9H9Me2)]. The latter is partially decarbonylated in vacuo to the hexacarbonyl species [NEt4][Co2W(µ3-CMe)(CO)6(η5-C2B9H9Me2)]. In contrast, treatment of the salts [X][W(CR)(CO)2(η5-C2B9H9Me2)](X = NEt4, R = Ph, C6H4Me-4, or C6H4Me-2; X = PPh4, R = Ph) with [Co2(CO)8] affords the hexacarbonyl–trimetal compounds [X][Co2W(µ3-CR)(CO)6(η5-C2B9H9Me2)]via the intermediacy of initially formed octacarbonyl products [X][Co2W(µ3-CR)(CO)8(η5-C2B9H9Me2)]. In the presence of carbon monoxide, the hexacarbonyl–trimetal compounds revert to the octacarbonyl, and a single-crystal X-ray diffraction study has been carried out on [PPh4][Co2W(µ3-CPh)(CO)8(η5-C2B9H9Me2)], which crystallises with half a molecule of CH2Cl2 per asymmetric unit. The anion consists of a triangle of metal atoms [Co–Co 2.502(3), Co–W 2.767(2) and 2.769(2)A] capped by the phenylmethylidyne ligand [µ3-C–Co 1.89(2) and 1.93(2), µ3-C–W 2.07(1)A]. The cobalt atoms each carry three terminal CO groups, but the two CO ligands attached to the tungsten semibridge the Co–W bonds [W–C–O 169(2) and 165(1)°]. The carbaborane ligand is η5-co-ordinated to the tungsten atom, and lies on the same side of the metal triangle as the µ3-CPh group. The salts containing the anions [Co2W(µ3-CR)(CO)6(η5-C2B9H9Me2)]– were shown by n.m.r. studies (1H, 11B-{1H}, 11B, and COSY 11B–11B) to have structures in which the carbaborane ligand forms two B–H⇀Co exopolyhedral bonds, one to each cobalt atom.