Metallocenes and Beyond for Propene Polymerization: Energy Decomposition of Density Functional Computations Unravels the Different Interplay of Stereoelectronic Effects

Stereoselective propene polymerization mechanisms promoted by C1-symmetric transition metal (TM) catalysts with nonmetallocene and ansa-metallocene ligands have been revisited by density functional theory (DFT) calculations combined with a molecular descriptor for steric analysis (%VBur) and a state-of-the-art interpretative tool based on the Activation Strain Model (ASM) and a Natural Energy Decomposition Analysis (NEDA). While DFT results suggested a close similarity for mechanisms and stereoselectivities for these catalyst classes, the ASM-NEDA analysis unraveled that different stereoelectronic effects play the dominant role depending on the ligand framework. The insights achieved by such analysis on the "naked"cationic active species were also confirmed by adding the counterion in the calculations, thus allowing a better understanding of olefin polymerization mechanism(s) governed by TM catalysts.