O‐Trityl phenoxy‐imino vanadium (III) complexes: synthesis, characterization, and catalysis on ethylene (co)polymerization

Abstract

Several phenoxy‐imine ligands bearing o‐trityl group in phenoxy moiety RN=CHArOH (Ar = C6H2(CPh3)tBu, R = 2,6‐Me2C6H3 (L1H); 2,6‐iPr2C6H3 (L2H); 3,5‐(CF3)2C6H3 (L3H); 3,5‐(OMe)2C6H3 (L4H); CHPh2 (L5H); CPh3 (L6H)) were synthesized and characterized by1H NMR and 13C NMR spectroscopy. The vanadium complexes based on these ligands LVCl2(THF)2 (1–6) were synthesized via conventional transmetalation reaction in moderate to high yields. Complexes 1–6 were fully characterized by FT‐IR, elemental analyses and the molecular structures of 1, 2·H2O, (2·H2O)2(μ‐Cl)2, 4, and 5 were confirmed by X‐ray crystallographic analysis in which the six‐coordinated vanadium centers are in a typical octahedral geometry. Upon activation with Et2AlCl in toluene, complexes 1–6 showed high activities in ethylene polymerization affording polymers with moderate molecular weight (5.9–11.8 × 104 Da). Moreover, in hexane or CH2Cl2, 1–6/Et2AlCl exhibited enhanced activities. When activated with MAO or MMAO in toluene, these complexes showed relatively low activities but afforded polymers with ultra‐high molecular weight (up to 3.30 × 106 Da). 1–6/Et2AlCl also showed high activities in ethylene/1‐hexene copolymerization at room temperature giving moderate molecular‐weight polymers (6.5–11.4 × 104 Da) with co‐monomer incorporation being of 6.0 ~ 7.8%.