A series of new zirconium complexes bearing bis(phenoxyketimine) ligands: Synthesis, characterization and ethylene polymerization

A series of new zirconium complexes bearing bis(phenoxyketimine) ligands, bis((3,5-di-tert-butyl-C6H2-2-O)R1Cdouble bond; length as m-dashN (2-R2-C6H4))ZrCl2 {R1 = Me, R2 = H (2a); R1 = Et, R2 = H (2b); R1 = Ph, R2 = H (2c); R1 = 2-Me-Ph, R2 = H (2d); R1 = 2-F-Ph, R2 = H (2e); R1 = 2-Cl-Ph, R2 = H (2f); R1 = 2-Br-Ph, R2 = H (2g); R1 = Ph, R2 = Me (2h); R1 = Ph, R2 = F (2i)}, have been prepared, characterized and tested as catalyst precursors for ethylene polymerization. Crystal structure analysis reveals that complex 2c has a six coordinate center in a distorted octahedral geometry with trans-O, cis-N, cis-Cl arrangement which possesses approximate C2 symmetry. When activated with methylaluminoxane (MAO), complexes 2a–2i exhibited high ethylene polymerization activities of 106–108 g PE (mol M h)−1. Compared with the bis(phenoxyimine) zirconium analogues bis((3,5-di-tert-butyl-C6H2-2-O)CHdouble bond; length as m-dashNC6H5)ZrCl2 (3), the introduction of substituent on the carbon atom of the imine double bond enhanced the catalytic activity and molecular weight of prepared polyethylene. Especially, when the H atom at the carbon atom of the imine double bond was replaced by 2-fluoro-phenyl with strong electronic-withdrawing property, complex 2e displayed the highest catalytic activity, and the polyethylene obtained possessed the highest molecular weight and melt point.