Copolymerization Mechanisms of Propylene and Norbornadiene Catalyzed by Zirconocene Complexes: A Density Functional Theory Study

Copolymerization mechanisms of norbornadiene (NBD) and propylene, catalyzed by three zirconocene catalysts (namely, rac‐Me 2 Si(2‐Me‐4‐Ph‐Ind) 2 ZrCl 2 /MAO ( catA ), rac‐Me 2 Si(Ind) 2 ZrCl 2 /MAO ( catB ), and rac‐CH 2 CH 2 (Ind) 2 ZrCl 2 /MAO( catC )), have been studied, using density functional theory computations. It has been found that the barrier (28.5 kcal mol −1 ) for the insertion of propylene to the [ Zr ] A ‐NBD‐PP 1 (the NBD insertion product) is significantly higher than those to [ Zr ] B ‐NBD‐PP 1 (22.9 kcal mol −1 ) and [ Zr ] C ‐NBD‐PP 1 (20.5 kcal mol −1 ), rationalizing the experimental observation that addition of NBD deactivated catA system but only lowered the catalytic activity of catB and catC systems. However, [ Zr ] A ‐NBD‐PP 1 can react with H 2 easily, which displaces NBD−PP 1 chain and gives active [ Zr ] A −H species to continue copolymerization, which is why the introduction of H 2 could recover the catalytic activity of catA system.