Unconventional Stereoerror Formation Mechanisms in Nonmetallocene Propene Polymerization Systems Revealed by DFT Calculations.

An unconventional mechanism for the stereoerror formation in propene polymerization catalyzed by -symmetric salalen-M systems (M = Zr, Hf) is suggested by DFT calculations. While propagation happens with the ligand in its conformation, a change of ligand wrapping mode from to is the main source of the lower stereoselectivities obtained with Zr and Hf. This is different for the Ti analogues, where the ligand - 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 (Δ) rather than to their mutual interaction (Δ)