Theoretical study of selectivity mechanisms in propylene polymerization with metallocene catalysts

Abstract The insertion mechanism in metallocene-catalyzed propylene polymerization is investigated through density functional theory calculations. Three paths corresponding to different orientations of the methyl group of the olefin have been studied and compared. The activation energy of the most favorable path is found to be 7.6 kcal/mol, which compares well with the experimental estimation, 10 kcal/mol. The activation energies for the other, less favorable, processes are 12.1 and 12.3 kcal/mol. The calculations show that propylene is coordinated very asymmetrically to the metal center. This asymmetry is assumed to be at the origin of the regio-selectivity of the reaction. On the other hand, the present computations confirm the importance of the “relay mechanism”, which correlates stereo-selectivity to steric interactions with the chain rather than to interactions with the ligand.