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

Abstract

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)Å] capped by the phenylmethylidyne ligand [µ₃-C–Co 1.89(2) and 1.93(2), µ₃-C–W 2.07(1)Å]. 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.