Synthesis, Structural Characterization, and Olefin Polymerization Behavior of Vanadium(III) Complexes Bearing Tridentate Schiff Base Ligands

Abstract

Vanadium(III) complexes bearing tridentate salicylaldiminato ligands (2a−f) [OC6H4CH═NL]VCl2(THF) (L = CH2CH2OMe, 2a; CH2CH2NMe2, 2b; CH2C5H4N, 2c; 8-C9H6N (quinoline), 2d; 2-MeSC6H4, 2e; 2-Ph2PC6H4, 2f) and tridentate β-enaminoketonato ligands [OC6H8CH═N-2-Ph2PC6H4]VCl2(THF) (2g) and [O(Ph)C═CHCH═N-2-Ph2PC6H4]VCl2(THF) (2h) were prepared from VCl3(THF)3 by treating with 1.0 equiv of the deprotonated ligands in tetrahydrofuran (THF). These complexes were characterized by FTIR and mass spectrometry as well as elemental analysis. Structures of complexes 2e, 2f, and 2h were further confirmed by X-ray crystallographic analysis. These complexes were investigated as catalysts for olefin polymerization in the presence of organoaluminum compounds. On activation with Et2AlCl, complexes 2a−h exhibited high catalytic activities toward ethylene polymerization (up to 20.64 kg PE/mmolV·h·bar) even at high temperature, suggesting these catalysts possess high thermal stability. Moreover, high molecular weight polymers with unimodal molecular weight distribution can be obtained, indicating the single site behavior of these catalysts. The copolymerizations of ethylene and norbornene or 1-hexene with catalysts 2a−h were also explored in the presence of Et2AlCl, which led to high molecular weight poly(ethylene-co-1-hexene)s (Mw up to 138 000) and poly(ethylene-co-norbornene)s (Mw up to 164 000). Catalytic activity, comonomer incorporation, and polymer molecular weight can be controlled in a wide range by the variation of catalyst structure and the reaction parameters such as Al/V molar ratio, comonomer feed concentration, and polymerization reaction temperature.