Ethylene polymerization by salicylaldimine nickel(ii) complexes containing a dibenzhydryl moiety

Abstract

The synthesis, characterization and ethylene polymerization properties of a series of salicylaldimine Ni(II) complexes with a dibenzhydryl moiety are described. These Ni complexes are designed to bear systematically varied electron donating and withdrawing substituents. These complexes are among the most active salicylaldimine Ni(II) catalysts in ethylene polymerization. Moreover, these complexes demonstrate good thermal stability, maintaining high activity at 80 °C. The polyethylene generated possesses a high molecular weight, moderate branching density and high melting temperature. Surprisingly, the electronic perturbations only exert moderate influence on the ethylene polymerization process despite the covalently close proximity of the electron donating or withdrawing substituents to the metal center. Comparing with the traditional iso-propyl substituted nickel analogue, these new complexes show up to an order of magnitude higher activity, generating polyethylene with much higher molecular weight, similar or slightly lower branching density and much higher melting temperature.