Synthesis, structures and ethylene polymerization behavior of half-metallocene chromium(III) catalysts bearing salicylaldiminato ligands

A series of half-metallocene chromium(III) complexes bearing a salicylaldiminato ligand, Cp'[2-R-1-4-R-2-6-(CH = NR3)C6H2O]CrCl [Cp' = Cp (1, 5), Cp* (2, 3, 4, 6, 7, 8); R-1 = Ph (1, 2, 3, 5, 6, 8), Pr-i (4), Bu-t (7); R-2 = H (1, 2, 3), Br (4), NO2 (5, 6, 7, 8); R-3 = Pr-i (1, 2, 5, 6, 7), Bu-t (3, 4, 8)], were synthesized. The structures of complexes 1, 3-5, 7-8 were determined by single crystal X-ray diffraction analysis. The X-ray crystallographic analysis indicates that these complexes adopt a pseudo-octahedral coordination environment with a three-legged piano stool geometry. Upon activation with a small amount of AlEt3, complexes 1-8 exhibit good to high catalytic activity for ethylene polymerization and produce ultra-high molecular weight polyethylene (PE) under mild conditions. The productivity of these complexes is relatively low when activated with AlMe3 and (AlBu3)-Bu-i. Both the productivity of these catalyst systems and the molecular weight of the produced PE can be tuned in a broad range by changing the ligands and the AlR3 co-catalyst.