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 . 1 H NMR spectroscopy suggests that these complexes exist as a single chiral C 2 ‐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 × 10 6 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 × 10 3 ) due to the enhanced rate of chain transfer to alkylaluminium groups during polymerization . Copyright © 2013 John Wiley & Sons, Ltd.