Bis(phenoxyimine)zirconium and -titanium Catalysts Affording Prevailingly Syndiotactic Polypropylenes via Opposite Modes of Monomer Insertion

Abstract

A zirconium(IV) complex bearing two N-(3-methylsalicylidene)-2,3,4,5,6-pentafluoroaniline and two Cl ligands has been synthesized (1). X-ray analysis indicates that 1 adopts a distorted octahedral structure with a trans-O, cis-N, and cis-Cl arrangement, similarly to previously reported complexes of this class. Polymerization of propene at room temperature in the presence of 1 activated by methylaluminoxane results in the production of poorly stereoregular, prevailingly syndiotactic polypropylene. The polymer microstructure is in agreement with a “chain-end” mechanism of steric control, with Pr = 0.67 (where Pr is the probability of a syndiotactic placement). End group analysis, also using deuterium labeling techniques, and NMR analysis of a copolymer of propene with trace amounts of [1-13C]-ethylene, indicate a prevailing primary insertion mode in both initiation and propagation, in contrast to the prevailingly secondary regiochemistry established for related bis(phenoxyimine) titanium catalysts. To discr...