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)C 6 H 4 HC N)] 2 C 6 H 4 (Ar = 2,6-Me 2 C 6 H 3 ( L 1 H 2 ) and 2,6- i Pr 2 C 6 H 3 ( L 2 H 2 )), were synthesized by the condensation reaction of o -phenylenediamine with the corresponding 2-(arylamino)benzaldehyde, and their zirconium and hafnium complexes, L 1 MCl 2 (M = Zr ( 1b ), Hf ( 1c )) and L 2 MCl 2 (M = Zr ( 2b ), Hf ( 2c )), were synthesized in high yields (61–66%) by the reactions of L 1 Li 2 and L 2 Li 2 with MCl 4 in toluene. Direct HCl-elimination reactions of L 1 H 2 with MCl 4 (M = Ti, Zr, Hf) in toluene at 140 °C under vacuum afforded the products L 1 HMCl 3 [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 1 H and 13 C 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 AlR 3 /Ph 3 CB(C 6 F 5 ) 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 × 10 4  g/mol).