Reactions of tetrachlorocyclopentadienyltantalum(V) derivatives with hexamethyldialuminium: 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.