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)R1CN (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)CHNC6H5)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.

Graphical abstractNine new zirconium complexes bearing bis(phenoxyketimine) ligands (2a–2i) have been prepared and used for ethylene polymerization. The steric and electronic effects caused by the introduction of substituents on the imine carbon atom (R1) of the ligand on catalytic properties are discussed in detail.Figure optionsDownload full-size imageDownload as PowerPoint slide