Synthesis and Characterization of [(C₅Me₄H)₂Al]⁺, an Initiator for the Polymerization of Isobutene. X-ray Crystal Structures of [(C₅Me₄H)₂Al(μ-Cl)]₂ and [(C₅Me₄H)₂Al][B(C₆F₅)₄]

The octamethylaluminocenium cation [Cp‘ 2 Al] + (Cp‘ = C 5 Me 4 H) was formed both by halide abstraction in the reaction between [Cp‘ 2 AlCl] 2 and AlCl 3 and by cyclopentadienide abstraction in the reaction between Cp‘ 3 Al and [CPh 3 ][B(C 6 F 5 )] 4 . [Cp‘ 2 Al] + is less thermally stable than [Cp* 2 Al] + (Cp* = C 5 Me 5 ) but is more active as an initiator for isobutene polymerization. The X-ray crystal structures of [Cp‘ 2 AlCl] 2 and [Cp‘ 2 Al][B(C 6 F 5 ) 4 ] are reported.