Activation of Bis(phenoxyimino)zirconium Polymerization Catalysts with Methylaluminoxane and AlMe₃/[CPh₃]⁺[B(C₆F₅)₄]^-

Abstract

The intermediates of olefin polymerization over homogeneous catalysts based on bis[N-(3-tert-butylsalicylidene)anilinato]zirconium(IV) dichloride {(LtBu)2ZrCl2} (1-tBu), bis[N-(3-methylsalicylidene)anilinato]zirconium(IV) dichloride {(LMe)2ZrCl2} (1-Me), and bis[N-(salicylidene)anilinato]zirconium(IV) dichloride {(LH)2ZrCl2} (1-H) with different activators {methylaluminoxane (MAO) and AlMe3/[CPh3]+[B(C6F5)4]-} have been studied by 1H and 13C NMR spectroscopy. Heterobinuclear ion pairs [(LtBu)2Zr(μ-Me)2AlMe2]+[Me-MAO]- (2-tBu) and [(LtBu)2Zr(μ-Me)2AlMe2]+[B(C6F5)4]- (2‘-tBu) are formed upon activation of 1-tBu with MAO and AlMe3/[CPh3]+[B(C6F5)4]-, respectively. These species are the precursors of the highly active intermediates of polymerization. In contrast, the activation of 1-Me with MAO results mainly in the formation of the tight ion pair [(LMe)2ZrMe+···Me-MAO-]. This ion pair is the precursor to a poorly active intermediate of polymerization. In the catalytic systems 1-H/MAO and 1-H/AlMe3/[CPh3]+[B(C6F5)4]-, the aluminum ion pairs [LHAl(μ-Me)(μ-Cl)AlMe2]+[Me-MAO]- and [LHAl(μ-Me)(μ-Cl)AlMe2]+[B(C6F5)4]-, which were inactive in ethylene polymerization, are predominantly formed. The isomeric composition of 2‘-tBu is close to that of the initial complex 1-tBu. The main route of the 1-tBu/MAO catalyst deactivation is the ligand transfer to aluminum with the formation of the complex LtBuAlMe2.