Comparative Theoretical Study on Homopolymerization of α-Olefins by Bis(cyclopentadienyl) Zirconocene and Hafnocene: Elemental Propagation and Termination Reactions between Monomers and Metals

A comparative quantum chemical study has been performed to shed light on the fundamental differences between hafnocenes and zirconocenes concerning reactions between the metals and α-olefin monomers, namely, ethene, propene, 1-butene, and 1-hexene. Analogous species along the α-olefin polymerization pathways were studied for bis(cyclopentadienyl) zirconocene and hafnocene, taking into account the structural variations of the first two monomer insertion steps and of the competitive chain-termination reactions. The results were analyzed as a function of both the metal and the monomer, the metal showing more distinct differences. The most notable difference in the reactions of the zirconocene and hafnocene can be seen in β-hydrogen transfer to metal, activation energies for which are significantly higher for the hafnocene.