Origin of the regiochemistry of propene insertion at octahedral column 4 polymerization catalysts: Design or serendipity?

The new octahedral column 4 catalysts bearing phenoxy-amine or phenoxy-imine ligands have opposite regioselectivities in propene polymerization. In this Communication, we report on a QM/MM investigation indicating that one of the key factors controlling the regiochemistry of propene insertion is the nature of the N atoms: steric and electronic effects related to the different hybridization synergically favor 1,2 or 2,1 insertion when the said N's are respectively of amine or imine type.