DFT investigation of the regiospecificity of a model catalyst site for propene polymerisation

Density functional theory calculations were used to study the mechanism of regioregular and regioirregular propene insertions to a model catalyst site (TiMg2Cl6CH3). Further regioregular insertions to Ti–2-butyl and Ti–2-methylpropyl bonds were simulated to study the reactivity after the first insertions. It was found that after the first regioregular insertion there exists two minimum energy conformations for the chain: α-agostic and β-agostic. The formation of a π-complex between propene and the active site was only possible with the α-agostic conformation. After the regioirregular insertion there is no minimum energy conformation with α-agostic interaction and so further insertions are hindered. In contrast to propene, ethene is found to be able to coordinate also to β-agostic site and is therefore able to reactivate polymerisation after a regioirregular insertion.