Living propene polymerization with bis(phenoxy-imine) group 4 metal catalysts: A theoretical study

Bis(phenoxy-imine)Ti catalysts with ortho-F-substituted phenyl rings on the N can promote living propene polymerization. On the basis of DFT calculations, it has been proposed that the "living" behavior originates from an unprecedented attractive interaction between the aforesaid ortho-F atoms and a β-H of the growing polymer chain, which would render the latter less prone to being transferred to the metal and/or to the monomer. In this paper, we report on a thorough full-QM and combined QM/MM investigation of representative model catalysts, demonstrating that the key factor is instead the repulsive nonbonded contact of the F-substituted rings with the growing polymer chain and an incoming propene molecule, which destabilizes the sterically demanding 6-center transition structure for chain transfer to the monomer. A conceptually similar substituent effect has been reported before for several metallocene and nonmetallocene catalysts.