ALKYLIDYNE(CARBABORANE) COMPLEXES OF THE GROUP-6 METALS .1. PROTON-INDUCED ALKYLIDYNE LIGAND MIGRATION

Treatment of carbon monoxide-saturated solutions of the salts [NEt4][W(= CR)(CO)2(eta(5)-C2B9H9Me2)] (R = C6H4Me-4 or Me) at ca. -78-degrees-C with HBF4.Et2O affords the complexes [W(CO)4{eta(5)-C2B9H8(CH2R)Me2}]. If these protonation reactions are carried out in the presence of PhC = CPh, the alkynetungsten complexes [W(CO)(PhC2Ph)2{eta(5)-C2B9H8(CH2R)Me2}] are formed via the intermediacy of dicarbonyl species [W(CO)2(PhC2Ph)2{eta(5)-C2B9H8(CH2R)Me2}]. The latter (R = C6H4Me-4) with PMe3 yields the compound [W(CO)(PMe3)(PhC2Ph){eta(5)-C2B9H8(CH2C6H4Me-4)Me2}]. Treatment of [NEt4][W(= CC6H4Me-4) (CO)2(eta(5)-C2B9H9Me2)] with HBF4.Et2O in the presence of CNBut yields [W(CO)2(CNBut)2{eta(5)-C2B9H8(CH2C6H4Me-4)Me2}], whereas if PPh3 is used instead of CNBut a tricarbonyl species [W(CO)3(PPh3){eta(5)-C2B9H8(CH2C6H4Me-4)Me2}] is isolated. However, the latter disproportionates in solution to afford the bis(triphenylphosphine) complex [W(CO)2(PPh3)2{eta(5)-C2B9H8(CH2C6H4Me-4)Me2}], crystals of which have been analysed by X-ray crystallography. The tungsten atom is eta(5) co-ordinated by the C2B9H8(CH2C6H4Me-4)Me2 ligand and is ligated by two CO and two PPh3 groups, having transoid arrangements. The CH2C6H4Me-4 substituent on the cage is bonded to the boron atom which is in the beta-site with respect to the two carbons in the open pentagonal activated CCBBB face of the nido-icosahedral C2B9 fragment. This geometry accounts for the NMR data (H-1, C-13-{H-1} and B-11-{H-1} for all the new complexes reported containing the C2B9H8(CH2R)Me2 cage system.