Influence of Steric and Electronic Perturbations on the Polymerization Activities of α-Iminocarboxamide Nickel Complexes

A series of N,O-bound, neutral nickel complexes containing α-iminocarboxamide, η1-CH2Ph, and PMe3 ligands were synthesized to examine the effect of steric and electronic variations at the site adjacent to the imine functionality. These complexes were subsequently activated with Ni(COD)2 for use in ethylene homopolymerization and ethylene/norbornene acetate (NBA) copolymerization reactions. As the bulk of the substituents is increased, one observes a progressive decrease in the rate of ring rotation, a more crowded coordination sphere around nickel, increased monomer consumption activity, and higher molecular weights of the products. Copolymerization reactions showed that the increased crowding around nickel decreases the reactivity of NBA relative to ethylene. As electron density is removed from the metal center, the catalytic species become more active toward ethylene and are more prone to interact with the functionality on NBA.