Theoretical design of higher performance catalysts for ethylene polymerization based on nickel-α-diimine

In this study, we investigated the reaction mechanism of Ni-α-diimine catalysts for ethylene (ET) polymerization using DFT calculations, focusing on structural and electronic factors that govern catalyst performance. Being the most active catalyst, Ni-Me was kept as a reference for analyzing pre-catalyst stability and reaction mechanisms. The first ET insertion, exhibiting the highest coordination free energy (G_c1) and activation free energy (ΔG‡1), is the rate-determining step. A comparative analysis of M-α-diimine catalysts with different transition metals (M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Ru(II), Rh(II), Pd(II), Ag(I), Cd(II)) revealed three distinct clusters. The cluster which contains (Ni(II), Ru(II), Mn(II), Rh(II), and Pd(II)) has moderate binding strength (G_c1 between -20 and -10 kcal mol^-1) and a reasonable activation barrier (ΔG‡1 between 10 and 15 kcal mol^-1), making it the most promising group for further study. With these criteria, Mn(II), Rh(II), Pd(II), Fe(II), and Ru(II) were identified as strong candidates for further catalyst development. Additionally, the bond distances and the percent buried volume (%V_Bur) were identified as key steric factors significantly influencing catalyst performance. These insights provide a rational framework for designing next-generation M-α-diimine catalysts with enhanced activity in ethylene polymerization.