Alkylidyne(carbaborane) complexes of the Group 6 metals. Part 1. Proton-induced alkylidyne ligand migration

Abstract

Treatment of carbon monoxide-saturated solutions of the salts [NEt₄][W(CR)(CO)₂(η⁵-C₂B₉H₉Me₂)](R = C₆H₄Me-4 or Me) at ca.–78 °C with HBF₄·Et₂O affords the complexes [W(CO)₄{η⁵-C₂B₉H₈(CH₂R)Me₂}]. If these protonation reactions are carried out in the presence of PhCCPh, the alkynetungsten complexes [W(CO)(PhC₂Ph)₂{η⁵-C₂B₉H₈(CH₂R)Me₂}] are formed via the intermediacy of dicarbonyl species [W(CO)₂(PhC₂Ph)₂{η⁵-C₂B₉H₈(CH₂R)Me₂}]. The latter (R = C₆H₄Me-4) with PMe₃ yields the compound [W(CO)(PMe₃)(PhC₂Ph){η⁵-C₂B₉H₈(CH₂C₆H₄Me-4)Me₂}]. Treatment of [NEt₄][W (CC₆H₄Me-4)(CO)₂(η⁵-C₂B₉H₉Me₂)] with HBF₄·Et₂O in the presence of CNBu^t yields [W(CO)₂(CNBu^t)₂{η⁵-C₂B₉H₈(CH₂C₆H₄Me-4)Me₂}], whereas if PPh₃ is used instead of CNBu^t a tricarbonyl species [W(CO)₃(PPh₃){η⁵-C₂B₉H₈(CH₂C₆H₄Me-4)Me₂}] is isolated. However, the latter disproportionates in solution to afford the bis(triphenylphosphine) complex [W(CO)₂(PPh₃)₂{η⁵-C₂B₉H₈(CH₂C₆H₄Me-4)Me₂}], crystals of which have been analysed by X-ray crystallography. The tungsten atom is η⁵ 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 β site with respect to the two carbons in the open pentagonal [graphic omitted] face of the nido-icosahedral C₂B₉ fragment. This geometry accounts for the NMR data (¹H, ¹³C-{¹H} and ¹¹B-{¹H}) for all the new complexes reported containing the C₂B₉H₈(CH₂R)Me₂ cage system.