Vanadium complexes bearing 8-anilide-5,6,7-trihydroquinoline ligands for ethylene (co-)polymerization

Abstract

Several trivalent and pentavalent vanadium complexes bearing 8-anilide-5,6,7-trihydroquinoline ligands were synthesized. These vanadium complexes were identified by elemental analysis, FTIR spectroscopy and NMR. Single crystals of trivalent vanadium complexes V2, V3′, and V4 and pentavalent vanadium complexes V5 and V7 were further obtained and identified by X-ray single crystal diffraction. In addition, the catalytic performance of these catalysts was adjusted by controlling the electronic and steric effects of substituents in the ligands. In the presence of diethylaluminium chloride, complexes V5–V7 displayed high activity (up to 82.8 × 10⁶ g mol_V⁻¹ h⁻¹) and good thermal stability toward ethylene polymerization. In addition, the copolymerization ability of complexes V5–V7 was evaluated, and complexes V5–V7 displayed high activity (up to 105.6 × 10⁶ g mol_V⁻¹ h⁻¹) and high copolymerization ability toward ethylene/norbornene copolymerization. By adjusting the polymerization conditions, copolymers with norbornene insertion ratios of 8.1%–30.9% can be obtained. Complex V7 was further studied for ethylene/1-hexene copolymerization, and the obtained copolymer displayed a moderate 1-hexene insertion ratio of 1.2%. Complex V7 displayed high activity and high copolymerization ability while having thermal stability. The results showed that 8-anilide-5,6,7-trihydroquinoline ligands with fused rigid-flexible rings were beneficial for vanadium catalysts.