Methylalumoxane (MAO)-derived MeMAO⁻ anions in zirconocene-based polymerization catalyst systems – a UV-Vis spectroscopic study

Abstract

Reaction of Me₂Si(Ind)₂ZrCl₂ with excess methylalumoxane (MAO) gives rise to ion pairs containing zirconocenium cations of the type [Me₂Si(Ind)₂ZrMe]⁺ in contact with two types of anions, MeMAO_A⁻ and MeMAO_B⁻, which differ in their coordinative strengths: More strongly coherent contact-ion pairs [Me₂Si(Ind)₂ ZrMe⁺**MeMAOB⁻] are converted by a sufficiently high excess of MAO to more easily separable contact-ion pairs [Me₂Si(Ind)₂ZrMe⁺**MeMAOA⁻], which react with AlMe₃ to form the outer-sphere ion pairs [Me₂Si(Ind)₂Zr(µ-Me)₂AlMe₂]⁺ MeMAO_A⁻, and are likely to be required also for the formation of the olefin-containing reaction complexes responsible for catalytic activity.