Density functional study on the role of electron donors in propylene polymerization using Ziegler-Natta catalyst

The role of electron donors in propylene polymerization using Ziegler-Natta model catalyst TiCl₂CH₃]⁺ has been investigated using density functional calculations at B3LYP/6-31G* level. Methyl benzoate (MBz) and para-methoxy methyl benzoate (p-OMe-MBz) are the electron donors considered in this study. We have found two major roles of these electron donors that match well with the corresponding experimental results. First, for both the catalysts having different electron donors, the propylene insertion in Ti-CH₃ bond in syn-fashion rather than anti-fashion has lower activation barriers (E_act). This indicates that the regioselectivity of propylene insertion is maintained in the presence of the electron donors. Secondly, co-ordination of electron donors is found to increase the activation barriers of propylene insertion, which explains the experimentally observed drop in catalytic activity of TiCl₂Me]⁺ on adding electron donors.