Effect of electron-withdrawing groups on the ring-opening polymerization of ε-caprolactone

The ring opening polymerization of ε-Caprolactone with Al centered catalysts consisting of two 2, 6-Dimethylphenoxy groups and a tridentate ligand is modelled with Gaussian09. The geometry optimizations and frequency analyses of the reactants, product, and two intermediate states were calculated at the B3LYP and 6-31G level of theory, and the energy calculations for the same states were carried out at the B3LYP and 6-311+G (d,p) level of theory with the SMD solvation method for toluene. Previous experiments showed that an increase in the number of electron withdrawing groups on the tridentate ligand resulted in an increased rate of polymerization. This effect can be attributed to the observation in the present work that electron withdrawing groups on the catalyst increased the electrophilicity of the Al center, lowering the energy of the HOMO and decreasing the HOMO – LUMO gap of the catalyst. This effect is particularly pronounced in the second ε-Caprolactone coordination and insertion