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

Abstract

The alkylaluminum-complexed zirconocene trihydride cation [(SBI)Zr(μ-H)_3(AliBu_2)_2]^+, which is obtained by reaction of (SBI)ZrCl_2 with [Ph_3C][B(C_6F_5)_4] and excess HAl^iBu_2 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 AlMe_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)_2AlMe_2]^+. The latter then becomes the resting state for further propene polymerization, which produces, by chain transfer to Al, mainly AlMe_2-capped isotactic polypropene.

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