Alkylidyne(carbaborane) complexes of the Group 6 metals. Part 2. Alkylidene group capture on protonation in the presence of chelating phosphines

Abstract

In CH₂Cl₂ solutions at ca.–78 °C the salts [PPh₄][W(CC₆H₄Me-4)(CO)₂(η⁵-C₂B₉H₉R′₂)](R′= Me or H) upon treatment with HBF₄·Et₂O, in the presence of dppm (Ph₂PCH₂PPh₂) or dppe (Ph₂PCH₂CH₂PPh₂), afford the complexes [[graphic omitted]Ph₂}(CO)₂(η⁵-C₂B₉H₉R′₂)](n= 1 or 2, R′= Me; n= 2, R′= H). The compound [[graphic omitted]Ph₂}(CO)₂(η⁵-C₂B₉H₁₁)] was similarly prepared from [NEt₄][W(CMe)(CO)₂(η⁵-C₂B₉H₁₁)], dppe and HBF₄·Et₂O. In contrast, treatment of [NEt₄][W(CMe)(CO)₂(η⁵-C₂B₉H₉Me₂)] in CH₂Cl₂ at –78 °C with HBF₄·Et₂O and dppe or dmpe (Me₂PCH₂CH₂PMe₂) gives the complexes [W(CO)₂L₂{η⁵-C₂B₉H₈(Et)Me₂}](L₂= dppe or dmpe). The molecular structure of [[graphic omitted]Ph₂}(CO)₂(η⁵-C₂B₉H₉Me₂)] has been established by a single-crystal X-ray diffraction study. Within the five-membered [graphic omitted] ring the bond distance are W–C 2.342(9), C–P 1.802(9), P–C 1.81 (1) and P–W 2.482(3)Å. The ligated carbon and phosphourus atoms of the ring, and the two essentially linearly bound CO ligands, form a pyramidal arrangement with the tungsten atom, the other side of which is co-ordinated by the nido-icosahedral C₂B₉H₉Me₂ cage in the usual η⁵ manner. The NMR spectra (¹H, ¹³C-{¹H}, ³¹P-{¹H} and ¹¹B-{¹H}) of the new compounds are reported and discussed in relation to their structures.