DFT Study of Olefin versus Nitrogen Bonding in the Coordination of Nitrogen-Containing Polar Monomers to Diimine and Salicylaldiminato Nickel(II) and Palladium(II) Complexes. Implications for Copolymerization of Olefins with Nitrogen-Containing Polar Monomers

An initial screening of late-transition-metal catalysts and nitrogen-containing polar monomers toward an incorporation of amines or nitriles in the polymer chain of polyolefins has been performed using density functional theory. Substrates of the type CH 2 CH(CH 2 ) n X (X = polar group) can bind either with the N-containing polar group or with the π moiety to the metal center of the catalyst. Monomer−catalyst combinations favoring the π complex over the N complex are promising, because the π-binding mode can subsequently lead to polymer growth. The stabilization energies for the π and N complexes of monomers of the type CH 2 CH(CH 2 ) n CN, CH 2 CH(CH 2 ) n NH 2, and CH 2 CH(CH 2 ) n N(CH 3 ) 2 with generic models for the recently reported nickel(II) and palladium(II) catalysts with diimine (“Brookhart”) and salicylaldiminato (“Grubbs”) ligands have been calculated. While the investigated polar monomers have been shown to form very strong metal−nitrogen bonds with the Brookhart nickel catalysts, the enamine prefers the π binding mode in its complexes with all model catalysts. Promising results have also been obtained for the coordination of nitriles and amines with the Grubbs nickel catalysts. The palladium systems show an even larger preference for π coordination than their nickel counterparts. An energy-decomposition scheme has been used to rationalize the relative strength of the catalyst−monomer bonds.