Zirconium complexes bearing bis(phenoxy‐imine) ligands with bulky o‐bis(aryl)methyl‐substituted aniline groups: synthesis,characterization and ethylene polymerization behavior

A series of bis(phenoxy‐imine) zirconium complexes bearing bulky o‐bis(aryl)methyl‐substituted aryl groups on the aniline moiety have been synthesized, characterized and tested as catalyst precursors for ethylene polymerization. ¹H NMR spectroscopy suggests that these complexes exist as a single chiral C₂‐symmetric isomer in the solution. X‐ray crystallographic analysis of the resulting biszwitterionic‐type adduct complex C1 · 2HCl reveals that the phenoxy‐imine groups function as a monodentate phenoxy ligand and the oxygen atoms are oriented trans to each other at the central metal atom. Using modified methylaluminoxane (MMAO) as co‐catalyst, C1 · 2HCl, C2–C6 exclusively produce linear aluminium‐terminated polyethylenes (Al‐PEs) with high activity (up to 16.89 × 10⁶ g PE (mol Zr h)^?1, suggesting that chain transfer to aluminum is the predominant termination mechanism. It is noteworthy that the introduction of an excessively bulky o‐bis(aryl)methyl substituent adjacent to the imine‐N produces low molecular‐weight Al‐PEs (M_v 1.6–10.1 × 10³) due to the enhanced rate of chain transfer to alkylaluminium groups during polymerization. Copyright © 2013 John Wiley & Sons, Ltd.