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

Abstract

Mixed ketoiminate/ketoimine/pentamethylcyclopentadienyl (Cp*) complex of zirconium, [(η 5-Cp*){CH 3C(O)CHC(NHR)CH 3}{CH 3C(O)CHC(NR)CH 3}ZrCl 2] (R=4 -CF 3Ph) ( 3) has been prepared in high yield by the reaction of one equivalent of 4-CF 3-phenyl-β-ketoimine ( 1a) and one equivalent of lithium 4-CF 3-phenyl-β-ketoiminate ( 2a) with one equivalent of Cp*ZrCl 3 in Et 2O. 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(NMe 2) 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.