Alkylation and activation of metallocene polymerization catalysts by reactions with trimethylaluminum: A computational study

Reactions between trimethylaluminum and selected zirconocene and hafnocene polymerization catalysts have been computationally studied at the MP2/TZVP level of theory. Dichloride precatalyst alkylation and the subsequent activation by ligand abstraction with trimethylaluminum were explored as a function of the catalyst structure. The alkylation reactions were found to proceed via two alternative routes depending on the structure of the catalyst. Concerning the activation of the alkylated precatalyst, interaction between trimethylaluminum and metallocene weakens the metal–ligand σ-bond, hence facilitating olefin uptake to some extent. Modification of the chemical environment of the Lewis-acidic Al site towards environments likely present in methylaluminoxane further facilitates the reaction, supporting the critical role of methylaluminoxane in catalyst activation.