Synthesis, structures and ethylenepolymerization behavior of half-metallocenechromium(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.