Density Functional Study of Neutral Salicylaldiminato Nickel(II) Complexes as Olefin Polymerization Catalysts

The recent discovery of the ability of salicylaldiminato Ni(II) complexes to promote ethylene polymerization creates a potential for a new class of olefin polymerization catalysts. The major advantage of this type of catalyst is that they produce a neutral active center and thereby avoid the ion-pairing problems encountered with the homogeneous single-site catalysts in current use. The present DFT study investigates the polymerization mechanism of these neutral complexes as well as the electronic and steric effects of various substituents on the catalyst backbone. The addition of electron-withdrawing or -releasing substituents on the 5 position of the salicylaldiminato ring was found to result in small changes in the energies of the reactions in the polymerization mechanism. This is most likely due to the substituents' remoteness from the active center. Changing the electronic nature of the donor atoms resulted in larger shifts in energy. Finally, bulky substituents such as 2,6-diisopropylphenyl and 9-anthracenyl groups were found to have the largest effect on the reaction barriers and enthalpies in a direction that should substantially increase catalyst activity.