Density Functional Theory Study On The Activity And Reaction Mechanism Of The Late Transition Metal Catalyst

Late transition metal catalysts have been become a hot issue in recent years due to the high activity, good tolerance for all kinds of functional group, low cost and excellent polymerization characteristics et al. In this paper, in order to better improve the catalytic performance of catalyst, the activity and reaction mechanism of late transition metal catalysts were systematic investigated with the quantum methods. The aim is to provide some theoretical basis for design, modification and research of such catalysts. The main contents of the paper are as follow:(1) The potential activities for two series of the bis(imino)pyridyliron complex pre-catalysts of ligands were very close on ethylene reactivity evaluated by the DFT-QEq method. All three spin states on central iron atom were calculated through Hirshfeld, Mulliken and QEq method to obtain the effective net charge. The results show the reasonable charge values obtained by QEq method, well reflecting the influences of substituents and revealing the correlations between the activity and effective net charge. All the series of iron complex pre-catalysts present the same tendency: the potential activities are elevated along with decreasing effective net charge on iron.(2) A series of unsymmetrical bis(imino)pyridylcobalt complexes was investigated by DFT-QEq method to correlate the net charges of cobalt center and their catalytic activities. The results show that: the effective net charge values on cobalt atom, calculated by QEq method more reasonable than which calculated by Hirshfeld and Mulliken method, better reflected the influences of substituents within their ligands and the correlation between the activity and effective net charge. The catalytic activities of these cobalt complexes in ethylene polymerization continuously increase along with higher values of the effective net charges on cobalt atom.(3) The activity for two series of cobalt complex pre-catalyst systems were investigated on the reaction activity by DFT-QEq method. It turned out that the correlation between the experimental activity and the obtained effective net charge values on cobalt atom by QEq method more reasonable than which obtained by Hirshfeld and Mulliken method. For the studied cobalt complex pre-catalyst system the activity increased with higher effective net charge value on cobalt atom, Comparison with two iron complex pre-catalyst systems with same ligand reported before showed that the charge variation on iron and cobalt metal atoms was the same as a function of different complexes and the charge value on the N3 atom in the ligand was similar with that of central metal atoms.(4) The reaction mechanism involving chain propagation and chain termination for a series of iron-based bis(imino)pyridine complexes have been carried out with the Gaussian 09 software package, using density functional theory. The type of catalyst can predict by comparing the energy barrier in chain propagation with that in chain transfer. Moreover, the results of deformation energy to further verify the predicted result, which is agreed with experiments observation.