Sterically hindered phosphine and phosphonium-based activators and additives for olefin polymerization

Abstract

The ability of phosphonium borates of the form [R3PH][B(C6F5)4], R2PHC6F4BF(C6F5)2 and R2PHC4H8OB(C6F5)3 as well as the phosphine-boranes R2PC6F4B(C6F5)2 to activate CpTiMe2(NPtBu3) for olefin polymerization was examined via both stoichiometric reactions and catalytic performance. In general these activators resulted in highly active ethylene polymerization catalysts, despite the generation of liberated phosphine donors. Independent experiments in which phosphines were added to the catalyst systems revealed the expected decrease in activity for small phosphines. However in the case of sterically encumbered phosphines, a marked increase in activity was observed. The cause of this increase is considered in the context of the concept of "frustrated Lewis pairs".