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

Abstract

A series of half-metallocene chromium(III) complexes bearing a salicylaldiminato ligand, Cp′[2-R1-4-R2-6-(CH = NR3)C6H2O]CrCl [Cp′ = Cp (1, 5), Cp* (2, 3, 4, 6, 7, 8); R1 = Ph (1, 2, 3, 5, 6, 8), iPr (4), tBu (7); R2 = H (1, 2, 3), Br (4), NO2 (5, 6, 7, 8); R3 = iPr (1, 2, 5, 6, 7), tBu (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 AliBu3. 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.