Doubly bridged ansa-zirconocenes based on the norbornadiene skeleton: A quantum mechanical and molecular mechanics study

A quantum mechanical study on the feasibility of doubly bridged ansa-zirconocenes based on the norbornadiene skeleton is presented. The enantioselectivity for the propene polymerization by these zirconocenes both with C-2 and C-s symmetry has been investigated by molecular mechanics analysis on models of catalytic intermediates corresponding to the monomer coordination step as well as on models of pseudotransition states relative to the possible monomer insertion reaction. According to our analyses, for suitable substitutions of the norbornadiene skeleton, the models are highly enantioselective. This suggests that both isotactic and syndiotactic polyolefins could be prepared by the corresponding catalytic systems.