A Density Functional Study of the Insertion Mechanism in MAO (Methylaluminoxane)-Activated, Cp2ZrMe2-Catalyzed Olefin Polymerization
 

Eva Zurek and Tom Ziegler
Department of Chemistry, University of Calgary, Calgary, Alberta, Canada, T2N 1N4
 
 

Abstract
 Density Functional Theory (DFT) has been used to study the insertion of ethylene into the [Cp2ZrMeRAlMe3]+[MeMAO]- (I) and [Cp2ZrMeR]+[MeMAO]- (II) ion pairs (R=Me, Prop) in gas phase and toluene solution. The transition states investigated include ones with a and b-agostic interactions as well as ones where the olefin is cis and trans to the counter-ion. In all cases the insertion barrier into I was found as being less than 20 kcal/mol and into II above 25 kcal/mol. This further supports the assertion that the active and dormant species have the structures suggested in I and II, respectively.
 The barrier for olefin uptake along with the energies of the various p-complexes for I have also been determined. Thus, different reaction profiles for the first and second insertion were examined and the most likely pathways identified.