Synthesis, characterization and ethylene reactivity of 2-ester-6- iminopyridyl metal complexes

A series of late-transition metal complexes such as iron (L)FeCl ₂ (3a-f), cobalt (L)CoCl₂ (4a-f), nickel (5a-f) and palladium(6a-f) complexes have been prepared by the reaction of 2-carboxylate-6-iminopyridine 2a-f [2-COOEt-6-(2,6-R₂C ₆H₃N=CCH₃)C₅H₃N (2a: R = CH₃, 2b: R = Et, 2c: R = i-Pr, 2d: R = F, 2e: R = Cl, 2f: R = Br)] with MCl₂ (M = Fe, Co, Ni or Pd). These complexes were characterized by elemental analysis, IR spectroscopy and X-ray crystallography. These complexes were tested for ethylene oligomerization and polymerization in the presence of MAO under various reaction conditions. The iron complexes exhibited high catalytic activities for ethylene polymerization/ oligomerization, whereas the cobalt complexes showed moderate activities for the polymerization and high activities for the oligomerization. In addition, the iron catalysts predominantly produced linear oligomers and polyethylene with vinyl group. Nickel complexes showed remarkably high catalytic activities for the ethylene oligomerization affording C₄-C₈ olefins as the main products, although the selectivity of α-olefin was very low. Palladium complexes showed moderate activity for the ethylene oligomerization and polymerization, and the oligomer product was only C₄. These facts indicated that the nature of the metal core strongly affects toward the catalyst behavior in these catalyses.