Methylaluminoxane (MAO), the archetypical cocatalyst in catalytic polymerization of olefins, has puzzled chemists for years. In the absence of the structural characterization of MAO, different methods of catalyst activation have been proposed. Here we systematically evaluate a mechanism where the activation proceeds via AlMe2+ abstraction from MAO, thereby generating the [MAO]-[Metallocene]+ ion pair. Various MAOs, produced by hydrolysis of trimethylaluminum, are included in the computational study, being analyzed as a function of the chemical environment of reactive Al sites. In addition to a ZrCp2Me2 metallocene, THF has been examined as the Lewis base. The reaction studies show the activation mechanism is plausible. Bond length analysis of the ion pairs suggest the capability for AlMe2+ abstraction can be effectively described in terms of MAO anionization potentials. The results are utilizable in identification of cocatalytically active sites and thereby in catalyst development.

Insights into activation of olefin polymerization catalysts by methylaluminoxane via formation of a dimethylaluminum cation

243rd National Meeting (2012)

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