Half-sandwich chromium(III) complexes containing salicylbenzoxazole and salicylbenzothiazole ligands for ethylene polymerization

Abstract

Half-sandwich chromium(III) complexes bearing salicylbenzoxazole ligands 2a-2f [L = R-2-(benzo[d]xazol-2-yl)-phenol (R = H (2a), R = 6-CH3 (2b), R = 6-tBu (2c), R = 4-OCH3 (2d), R = 4-Cl (2e), R = 4-NO2 (2f)] and salicylbenzothiazole ligands 3a-3f [L = R-2-(benzo[d]xazol-2-yl)-phenol (R = H (3a), R = 6-CH3 (3b), R = 6-tBu (3c), R = 4-OCH3 (3d), R = 4-Cl (3e), R = 4-NO2 (3f)] were synthesized by the salt-elimination reaction of CpCrCl2(THF) and the sodium salt of the corresponding ligands in THF at −78 °C. The molecular structures of complexes 3a and 3e are confirmed by single-crystal X-ray crystallographic analysis. Upon the activation of a small amount of AlEt3, all the half-sandwich chromium(III) complexes showed moderate to high catalytic activities for ethylene polymerization and afforded high molecular weight polyethylene (PE).