Reactions of tetrachlorocyclopentadienyltantalum(V) derivatives with hexamethyldialuminum. Crystal and molecular structure of dichlorodimethylpentamethylcyclopentadienyltantalum(V)

The reaction of [TaCpCl4](CP = η5-C5Me5, η5-C5H4SiMe3 or η5-C5H3(SiMe3)2) with Al2Me6 leads to [TaCpCl3Me] (Cp = η5-C5Me5 (2a), η5-C5H4SiMe3 (2b), or η5-C5H3(SiMe3)] (2c)) and [TaCpCl2Me2] (CP = η5 - C5Me5 (3a)). The structure of 3a has been determined by X-ray diffraction. The compound crystallizes in the monoclinic space group P21/m, with Z = 2, a 6.770(3), b 13.969(3) and c 8.395(2) Å, β 112.25(3)°; the structure was refined to R = 0.059 and wR = 0.095 for 1197 independent reflections having F > 4σ(F). The Ta atom may be considered as being five-coordinate if the substituted cyclopentadienyl ring occupies a single coordination site, and the geometry at the metal approximates to a square-based pyramid