The Aluminocenium Cation [AI(C_5H_5)_2] A Highly Effective Initiator for the Cationic Polymerization of Isobutene

摘要

The role of aluminum reagents as Lewis acids and as activators for olefin polymerization catalysts is well documented. Very little is known, however, about the chemistry of cationic organoaluminum compounds [A1R_2]~ + for which very high Lewis aciditycan be expected. Some donor-stablized cationic complexes such as [AlMe_2(crown)]~+, [(EtAI)_2(diazacrown)]~(2+), and [Al{C(SiMe_3)_2py}_2]~+ have been structurally characterized, and recently Schnockel et ai. reported the formation of the decamethylaluminocenium cation [AlCp_2*]~+ by the dispro-portionation of [AlCp_2*]_4 in the presence of AIC1, (Cp* = C_5Me_5). The reactivity of such cationic organoaluminum complexes has to our knowledge not been explored. We report here the synthesis of the unsubstituted aluminocenium cation. [AICp_2]~+, (Cp = C_5H_5) and its reactivity as an initiator for cationic polymerizations.