Zirconium and hafnium complexes with new tetra-azane ligands: Synthesis, characterization and catalytic properties for ethylene polymerization

Abstract

Two new anilido-imine tetra-azane ligands, 1,2-[(2′-(ArNH)C6H4HCN)]2C6H4 (Ar=2,6-Me2C6H3 (L1H2) and 2,6-iPr2C6H3 (L2H2)), were synthesized by the condensation reaction of o-phenylenediamine with the corresponding 2-(arylamino)benzaldehyde, and their zirconium and hafnium complexes, L1MCl2 (M=Zr (1b), Hf (1c)) and L2MCl2 (M=Zr (2b), Hf (2c)), were synthesized in high yields (61–66%) by the reactions of L1Li2 and L2Li2 with MCl4 in toluene. Direct HCl-elimination reactions of L1H2 with MCl4 (M=Ti, Zr, Hf) in toluene at 140°C under vacuum afforded the products L1HMCl3 [M=Ti (1a′), Zr (1b′), Hf (1c′)] with a partially deprotonated tridentate ligand in good to high yields (48–70%). All the new complexes were characterized by 1H and 13C NMR spectroscopy and the molecular structures of 1b and 2c were determined by single crystal X-ray diffraction analysis. The metal centers in both complexes are six-coordinated with a distorted octahedral geometry. Upon activation with MAO or AlR3/Ph3CB(C6F5)4, complexes 1b–1c and 2b–2c all exhibit moderate catalytic activity for ethylene polymerization and produce linear polyethylene with ultra-high molar masses (100–184×104g/mol).