Vanadium(III) complexes bearing phenoxy-phosphine ligands (2ag) (2-R1-4-R2-6-PPh2-C6H2O)VCl2(THF)2 (2a: R1 = R2 = H; 2b: R1 = F, R2 = H; 2c: R1 = Ph, R2 = H; 2d: R1 = tBu, R2 = H; 2e: R1 = R2 = Me; 2f: R1 = R2 = tBu; 2g: R1 = R2 = CMe2Ph) were prepared from VCl3(THF)3 by treating with 1.0 equiv of the ligand in tetrahydrofuran (THF) in the presence of excess triethylamine (TEA). The reaction of VCl3(THF)3 with 2.0 equiv of the ligand in THF in the presence of excess TEA afforded vanadium(III) complexes bearing two phenoxy-phosphine ligands (3cf). These complexes were characterized by FTIR and mass spectrum as well as elemental analyses. Structures of 2f and 3c were further confirmed by X-ray crystallographic analyses. Complexes 2ag and 3cf were employed as the catalysts for ethylene polymerization under various reaction conditions. On activation with Et2AlCl, these complexes exhibited high catalytic activities (up to 41.3 kg PE/mmolV center dot h center dot bar) even at high temperature (70 degrees C), and produced high molecular weight polymer with unimodal molecular weight distributions, indicating the polymerization took place in a single-site nature. Complexes 3cf displayed better thermal stability than the corresponding complexes 2ag under similar conditions. In addition, copolymerizations of ethylene and 1-hexene with precatalysts 2ag were also explored in the presence of Et2AlCl. Catalytic activity, comonomer incorporation, and properties of the resultant polymers can be controlled over a wide range by tuning catalyst structures and reaction parameters.(C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012