A SCF-Xα-SW molecular-orbital study of a possible reaction path for Ziegler–Natta catalysis

Abstract

SCF-Xα-SW molecular-orbital calculations for the coordination complex [CH3TiCl4 (C2H4)]n = 0,−2, which is postulated to be an intermediate in Ziegler–Natta polymerization reactions, demonstrate that the energy gap between the lower lying Ti-alkyl orbital and the higher Ti (3dyz)-olefin (π*) orbital is sufficiently large (0.9 eV for n = 0 and 1.5 eV for n = −2) to make the Cossee mechanism for the propagation step seem unlikely. A series of calculations for CH3TiCl4(C2H4), where the alkyl and olefin groups are moved closer together in a sequence of concerted steps, suggests that this migration is a plausible mechanism for the polymerization reaction.