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

摘要

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 CI 2HCI 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, CI 2HCI, C2-C6 exclusively produce linear aluminium-terminated polyethyl-enes (AI-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(aryi)methyl substit-uent adjacent to the imine-N produces low molecular-weight AI-PEs [M_v 1.6-10.1 × 10~3) due to the enhanced rate of chain transfer to alkylaluminium groups during polymerization.