Cationic Alkylaluminum-Complexed Zirconocene Hydrides as Participants in Olefin Polymerization Catalysis

摘要

The alkylaluminum-complexed zirconocene trihydride cation [(SBI)Zr(μ-H)₃(AliBu₂)₂]+, which is obtained by reaction of (SBI)ZrCl₂ with [Ph₃C][B(C₆F₅)₄] and excess HAliBu₂ in toluene solution, catalyzes the formation of isotactic polypropene when exposed to propene at −30 °C. This cation remains the sole observable species in catalyst systems free of AlMe compounds. In the presence of AlMe₃, however, exposure to propene causes the trihydride cation to be completely converted, under concurrent consumption of all hydride species by propene hydroalumination, to the doubly Me-bridged cation [(SBI)Zr(μ-Me)₂AlMe₂]+. The latter then becomes the resting state for further propene polymerization, which produces, by chain transfer to Al, mainly AlMe₂-capped isotactic polypropene.