Thermally stable vanadium(v) complexes bearing bidentate phenoxy-phosphine ligands: synthesis, characterization, and catalytic properties for alkene polymerization

Abstract

A series of novel imido-vanadium(V) complexes bearing bidentate phenoxy-phosphine ligands was synthesized and characterized by NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. These complexes exhibited excellent catalytic performance in olefin polymerization. In ethylene polymerization, complex C1 exhibited high catalytic activity (139.4 × 10⁶ g_PE (mol_V)⁻¹ h⁻¹), robust thermal stability (29.8 × 10⁶ g_PE (mol_V)⁻¹ h⁻¹ at 100 °C), broad solvent applicability, and long catalytic lifetime (60 min). Additionally, the produced PEs exhibited high molecular weights, up to 58.5 × 10⁴ Da. In ethylene/1-hexene and ethylene/norbornene copolymerization, random copolymers with tunable 1-hexene (1.9–4.5 mol%) and norbornene (23.5–29.5 mol%) incorporations were generated with exceptional efficiency, up to 58.9 × 10⁶ g_polymer (mol_V)⁻¹ h⁻¹. Moreover, in ethylene/polar monomer copolymerization, functionalized copolymers containing adjustable hydroxyl group units (1.79–4.18 mol%) were prepared. Combining density functional theory (DFT) calculations with polymerization experiments, the steric and electronic effects of substituents on the ligand framework were systematically investigated to elucidate their influence on catalytic behaviors, establishing comprehensive correlating relationships of structure–activity-selectivity.