Stereochemistry of First Monomer Insertion into Metal−Methyl Bond: A Tool for Evaluating Ligand−Monomer Interactions in Propene Polymerization with Metallocene Catalysts

Abstract

Propene has been polymerized with three different metallocene complexes: Me2Si(Ind)2ZrCl2 (I), Me2Si(BenzInd)2ZrCl2 (II), and Me2Si(MeBenzInd)2ZrCl2 (III) by using 13C-enriched cocatalyst MAO/Al(13CH3)3. The stereochemical analysis of selectively 13C-enriched methyl chain end groups has shown that, while a moderate first step enantioselectivity is present with catalyst I, the bulky benzannelated substituents (catalysts II and III) lead to an almost total lack of steric control on the first monomer insertion. The methyl substitution in the 2-position of cyclopentadienyl ring (catalyst III) does not seem to influence the choice of the face.