Bis-amide and amine bis-amide ligands in M(IV) (M=V, Cr, Mn) based olefin polymerization catalysts: a theoretical study

Recent discoveries of active early transition metal olefin polymerization catalysts with positive d-electron counts indicate the potential for a wide variety of new catalysts of this type. To increase our understanding of the influence of d-electrons on these olefin polymerization catalysts, we have used density functional theory methods to model a series of otherwise analogous d1 V, d2 Cr, and d3 Mn systems with an amine and two amide ligands. Second-row analogues are also briefly examined. The preferred geometries of the systems change dramatically in these three different metal systems due to the changes in d orbital occupation. These changing geometric preferences are explained using a valence bond based model of the bonding. The ligands are then linked with ethyl bridges, restricting the possible conformers and changing the catalytic properties dramatically. Both the V and Cr tethered systems are predicted to be good candidates for polymerization catalysts, with the Cr system predicted to be a living polymerization catalyst, with a termination barrier 13.5 kcal mol−1 higher than its insertion barrier.