Highly active chromium(iii) complexes based on tridentate pyrazolyl pyridyl ligands for ethylene polymerization and oligomerization

Abstract

A set of new chromium(III) [Cr(III)] complexes based on the tridentate ligand HC(Pz)₂Py (Pz = pyrazole; Py = pyridine) and its derivatives were prepared, characterized, and evaluated for ethylene polymerization/oligomerization. X-ray single-crystal analyses of the Cr(III) complexes showed tridentate coordination on the fac-octahedral Cr sphere. Upon activation with methylaluminoxane (MAO), the precatalysts and the ligands L1–L3 mixed in situ with Cr(acac)₃ were highly active and generally produced polyethylene as a major product. Their catalytic performances were markedly affected by the substituents on the methine carbon atom of the ligands and reaction conditions.