Methylalumoxane (MAO)-Derived MeMAO− Anions in Zirconocene-Based Polymerization Catalyst Systems – A UV-Vis Spectroscopic Study

Reaction of Me 2 Si(Ind) 2 ZrCl 2 with excess methylalumoxane (MAO) gives rise to ion pairs containing zirconocenium cations of the type [Me 2 Si(Ind) 2 ZrMe] + in contact with two types of anions, MeMAO A - and MeMAO B - , which differ in their coordinative strengths: More strongly coherent contact-ion pairs [Me 2 Si(Ind) 2 Zrme +.. MeMAO B - ] are converted by a sufficiently high excess of MAO to more easily separable contact-ion pairs [Me 2 Si(Ind) 2 ZrMe +.. MeMAO A - ], which react with AlMe 3 to form the outer-sphere ion pairs [Me 2 Si(Ind) 2 Zr(μ-Me) 2 AlMe 2 ] MeMAO A - , and are likely to be required also for the formation of the olefin-containing reaction complexes responsible for catalytic activity.