Alkylidyne(carbaborane) complexes of the Group 6 metals. Part 5. Protonation studies on [NEt4][W(CC6H4OMe-2)(CO)2(η5-C2B9H9Me2)]

Abstract

Dichloromethane solutions of [NEt₄][W(CR)(CO)₂(η⁵-C₂B₉H₉Me₂)](R = C₆H₄OMe-2) at –78 °C on treatment with HBF₄·Et₂O in the presence of the substrates L = CO, PPh₃, PHPh₂, CNBu^t and PhC₂Ph afford the complexes [W(CO)₂L₂{η⁵-C₂B₉H₈(CH₂R)Me₂}](L = CO, PHPh₂ or CNBu^t), [W(CO)₃(PPh₃){η⁵-C₂B₉H₈(CH₂R)Me₂}] and [W(CO)(PhC₂Ph)₂{η⁵-C₂B₉H₈(CH₂R)Me₂}] respectively. The corresponding protonation reaction employing dppm (Ph₂PCH₂PPh₂) as the substrate yields [W(CO)₂(dppm){η⁵-C₂B₉H₈(CH₂R)Me₂}] as the major product, together with small quantities of [[graphic omitted]Ph₂}(CO)₂(η⁵-C₂B₉H₉Me₂)]. The structure of [W(CO)₃(PPh₃){η⁵-C₂B₉H₈-(CH₂R)Me₂}] has been established by X-ray diffraction. The tungsten atom is η⁵ co-ordinated by the nido-icosahedral fragment C₂B₉H₈(CH₂R)Me₂. In the latter the exopolyhedral CH₂R group is bonded to the boron atom which is in the β position with respect to the two carbon atoms in the open pentagonal [graphic omitted] face of the cage ligating the tungsten. The latter also carries three terminally bound CO groups and the PPh₃ ligand. Addition of aqueous HI to CH₂Cl₂ solutions of [NEt₄][W(CR)(CO)₂(η⁵-C₂B₉H₉Me₂)] affords the salt [NEt₄][WI(CO)₃{η⁵-C₂B₉H₈(CH₂R)Me₂}]. In the latter there is a 2,1,8 arrangement for the non-boron vertices of the WC₂B₉ icosahedron, in contrast with the closo-3,1,2-WC₂B₉ structures of the other products. The NMR data (¹H, ¹³C-{¹H}, ¹¹B-{¹H} and ³¹P-{¹H}) for the new compounds are reported and discussed in relation to the molecular structures.