Bis(β‐enaminoketonato) vanadium (III or IV) complexes as catalysts for olefin polymerization

Abstract Bis(β‐enaminoketonato) vanadium(III) complexes ( 2a–c ) [O(R 1 )CC(H) x C(R 2 )NC 6 H 5 ] 2 VCl(THF) and the corresponding vanadium(IV) complexes ( 3a–c ) [O(R 1 )CC(H) x C(R 2 ) NC 6 H 5 ] 2 VO (R 1 = (CH 2 ) 4 , R 2 = H, x = 0, a ; R 1 = C 6 H 5 , R 2 = H, x = 1, b ; R 1 = C 6 H 5 , R 2 = C 6 H 5 , x = 1, c ) have been synthesized from VCl 3 (THF) 3 and VOCl 2 (THF) 2 , respectively, by treating with 2.0 equivalent β‐enaminoketonato ligands in tetrahydrofuran. Structures of 2b and 3a–c were further confirmed by X‐ray crystallographic analysis. The complexes were investigated as the catalysts for ethylene polymerization in the presence of Et 2 AlCl. Complexes 2a–c and 3a–c exhibited high catalytic activities (up to 23.76 kg of PE/mmol V h bar), and afforded polymers with unimodal molecular weight distributions at 70 °C indicating the good thermal stability. The catalytic behaviors were influenced not only by the oxidation state of the catalyst precursors but also by the ligand structures. Complexes 2a–c and 3a–c were also effective catalyst precursors for ethylene/1‐hexene copolymerization. The influence of polymerization parameters such as reaction temperature, Al/V molar ratio and hexene feed concentration on the ethylene/hexene copolymerization behaviors have bee also investigated in detail. In addition, the agents such as AlMe 3 , Al i Bu 3 , MeMgBr, MgCl 2 , and ZnEt 2 were applied to control the molecular weight and molecular weight distribution modal. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3062–3072, 2010