Activity of phenoxy-imine titanium catalysts in ethylene polymerization: A quantum chemical approach

Abstract

The mechanism of ethylene polymerization on phenoxy-imine (FI) titanium catalysts was studied theoretically to identify the major factors affecting the catalytic activity. Geometry optimizations of FI ligands, octahedral titanium dichloride complexes, active cationic species, and their π‐complexes with ethylene as well as calculations of the energy profile of chain propagation were performed at the BP86-D3 level. We found that the calculated energy gaps between frontier orbitals (HOMO and LUMO) in the active cations of the catalysts correlate with the experimental activity values. High activities of FI catalysts with α‐Cumyl groups were attributed to smaller HOMO-LUMO gaps due to hyperconjugation between π-systems of α‐Cumyl and (N‐aryl)salicylaldimine moieties in the active cations. The correlation provides a qualitative estimate of the catalytic activity for further design of new FI titanium complexes.