Unconventional Stereoerror Formation Mechanisms in Nonmetallocene Propene Polymerization Systems Revealed by DFT Calculations
Eugenio Romano, Peter H. M. Budzelaar, Claudio De Rosa, Giovanni Talarico
Abstract
An unconventional mechanism for the stereoerror formation in propene polymerization catalyzed by C1-symmetric salalen-M systems (M = Zr, Hf) is suggested by DFT calculations. While propagation happens with the ligand in its fac-mer conformation, a change of ligand wrapping mode from fac-mer to fac-fac is the main source of the lower stereoselectivities obtained with Zr and Hf. This is different for the Ti analogues, where the ligand fac-mer wrapping mode does not play a role. Activation strain analysis indicates that the preference for a chain stationary mechanism of the Zr/Hf species is due to the energy required to distort the reactants (ΔEStrain) rather than to their mutual interaction (ΔEInt).