Zirconium complexes based on an ethylene linked amidinate–amido ligand: synthesis, characterization and ethylene polymerization

Abstract

The dimer lithium complex 3 and zirconium complexes 4–6 were synthesized and characterized. Monomer/dimer zirconium complexes 4–6 were synthesized by changing the molar ratio of ZrCl₄ : ligand. Their structures were confirmed by X-ray diffraction analysis, which showed a distorted octahedral geometry. Complexes 5 and 6 were zirconium trichloride compounds, while complex 4 was not a zirconium chloride species. The catalytic behaviors of complexes 4–6 were investigated in the presence of MAO as a cocatalyst. It was found that the catalytic activities of these zirconium complexes toward ethylene polymerization were closely related to the bonding patterns (η³:η¹, η³ or η¹), the number of chlorine atoms in the procatalysts and the availability of the coordination site in the molecule. Zirconium trichloride complex 5 showed the highest catalytic activity mainly because of its η¹ bonding pattern.