Synthesis, structure and ethylene polymerization behavior of zirconium complexes with chelating ketoiminate ligands

Mixed ketoiminate/ketoimine/pentamethylcyclopentadienyl (Cp*) complex of zirconium, [(η5-Cp*){CH3C(O)CHC(NHR)CH3}{CH3C(O)CHC(NR)CH3}ZrCl2] (R=4-CF3Ph) (3) has been prepared in high yield by the reaction of one equivalent of 4-CF3-phenyl-β-ketoimine (1a) and one equivalent of lithium 4-CF3-phenyl-β-ketoiminate (2a) with one equivalent of Cp*ZrCl3 in Et2O. Bis(ketoiminate)zirconium dichloride complexes, 4 and 6, have been also prepared in high yield by the reaction of amine elimination of ketoimine ligands, respectively 1a and 1b, with Zr(NMe2)4 and followed by chlorination reaction with TMSCl. The X-ray crystallography reveals that the compound 3 is based on distorted octahedral geometry containing a ketoimine and a ketoiminate. The ketoiminate ligand coordinates to the zirconium as a bidentate ligand, leaving the metal center coordinatively unsaturated and thus leading to an additional binding of a ketoimine ligand to the metal to stabilize the complex 3. The zirconium complexes 3, 4 and 6 provide the moderate activity for the polymerization of ethylene in the presence of MMAO cocatalyst. Low molecular weight and high density polyethylene was obtained.