Heteroatom-substituted carbene complexes of high-valent tungsten:: Tp′W(O)X(=C(R)OSiR3) derivatives

Reaction of Tp'W(O)(I)(CO) (1; Tp'= hydridotris(3,5-dimethylpyrazolyl)borate) with MeLi followed by trapping of the resultant anion by ClSiPh2Me leads to the formation of a single isomer of the tungsten(VI) heteroatom-substituted carbene complex Tp'W(O)(I)(=C(Me)-OSiPh2Me) (5a). The connectivity of complex 5a was confirmed by X-ray crystallography and spectral data. The acyl intermediate in the reaction, [Tp'W(O)(I)(O)Me)] [Li] (6), was observed by spectroscopic techniques. Trapping of the acyl intermediate 6 with H+ yields the neutral hydroxy carbene complex Tp'W(O)(I)(=C(Me)OH) (5c). Reaction of complex 1 with PhLi generates the anionic phenyl-acyl complex [Tp'W(O)(I)(C(O)Ph)][Li] (8), which may be trapped with ClSiPh2Me, yielding the phenyl carbene complex Tp'W(O)(I)(=C(Ph)-OSiPh2Me) (7). Carbene complex 5a reacts with AgSO3CF3 to form silver iodide and a coordinated triflate complex, Tp'W(O)(OSO2CF3)(=C(Me)OSiPh2Me) (9). In contrast to the acyl product formed with MeLi and 1, combining LiCuMe2 with 1 leads to the replacement of iodide by a methyl group to form Tp'W(O)(Me)(CO) (2). Protonation of this methyl tungsten complex (2) in CH2Cl2 in the presence of acetonitrile yields methane and the cationic nitrile adduct [Tp'W(O)(CO)(NCMe)](+) (3), while protonation of 2 in neat acetonitrile produces a cationic hydroxy carbene complex, [Tp'W(O)(NCMe)(=C(Me)OH)](+) (4).