Topological and Electronic Properties of Chlorine-Substituents on the α-Diimine Ni-based Catalysts

Abstract

The effect of substituent nature and position on a series of late transition metal catalysts based on nickel (A–D) was investigated practically and theoretically. Catalyst A bearing isopropyl groups on the ortho position showed the highest activity while for the ortho and para chlorine substituted catalysts B–D insignificant activities were observed. These experimental results were confirmed by theoretical study on the (pre)catalysts. Based on that, thermodynamics, atomic/molecular effective parameters such as bond distances, bond angles, band gap or chemical hardness, charge of Mulliken on Ni center, electronic chemical potential, global electrophilicity index and also activation energy of the pre-catalyst through the alkylation were calculated. To pursue the steric and electronic effects of substituent on the axial and equatorial sites of active center, electronic density, electron location function, localized orbital locator graphs as topological properties were studied. As a result, complex A with lower activation energy for alkylation, higher stability, greater Mulliken charge on Ni center and high electronic density around the active center was found as a highly active catalyst. In addition, polymerization conditions such as polymerization temperature and ethylene pressure showed significant effect on the catalysts productivity and branching density of the produced polyethylene.