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

摘要

The alkylaluminum-complexed zirconocene trihydride cation [(SBI)Zr(μ-H)_3(AI~iBu_2)_2]~+, which is obtained by reaction of (SBI)ZrCI_2 with [Ph_3C][B(C_6F_5)_4] and excess HAI~jBu_2 in toluene solution, catalyzes the formation of isotactic polypro-pene when exposed to propene at -30 ℃. This cation remains the sole observable species in catalyst systems free of AIMe compounds. In the presence of AIMe_3, 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)_2AIMe_2]~+. The latter then becomes the resting state for further propene polymerization, which produces, by chain transfer to Al, mainly AIMe_2-capped isotactic polypropene.