Tuning the Relative Energies of Propagation and Chain Termination Barriers in Polyolefin Catalysis through Electronic and Steric Effects

A computational exploration of the predicted molecular weights for Ti- and Zr-catalyzed olefin polymerizations shows that there are considerable opportunities for electronic tuning. Ligand variation mainly affects the propagation rate, whereas chain transfer to the monomer is hardly affected by electronic factors. The results are analyzed in terms of the effects of ligand variation on the relative energies of “connected couples” of reactant local minima and the corresponding transition states on the basis of the Hammond postulate and the Curtin–Hammett principle. For the constrained-geometry catalysts (CGCs) and bis(amido) systems studied, better donating ligands increase the preference for a “planar” metal environment and produce higher molecular weights.