Diacetyl Monoxime Hydrogenation Reaction Catalyst And Its Catalytic Activity Theory Research

Theoretical studies on series of different ligand and metal ion of transition metal complex catalyst which were used for the hydrogenation of diacetyl monoxime(DAM) to tetramethylpyrazine, were carried out by the method of density functional theory(DFT). Their electronic and geometric structures were obtained. The theoretical results has been investigated according to the frontier molecular orbital energies, molecular orbital compositions, natural charge populations and binding energy of the complexes. Some factors and laws affecting the catalytic activity of the complexes have been studied, and they can be used as theoretical references in the design of the complex catalyst and the research of interaction between the reactant(DAM) and the complex. The conclusions are given as follows:(1) Ligand effects on electronic structures and the catalytic properties of complexesThe correlation between the electronic structures of the triphenyl type of complexes and their catalytic activity was investigated. The lower theΔε_L-H energy of the complex catalyst Pd⁽⁰⁾L₂ (L=NPh₃, PPh₃, AsPh₃, O=PPh₃), the higher the catalytic activity of the complexes. The results showed that the catalytic activity of the complexes were related withΔε_L-H. The higher the E_HOMO- of the complexes, the closer the E_HOMO- of the complexes to the E_LUMO of DAM, the higher the catalytic activity. The calculation of the natural bond orbital and binding energy showed, the stability of the complexes was closely correlated with catalytic activity. The weaker the stability of the complexes, the easier the coordination of the complexes with DAM, the higher the catalytic activity.The correlation between the electronic structures of the pyridine type of complexes and their catalytic activity was investigated. The higher the E_HOMO- of the complex catalyst Pd⁽⁰⁾L₄ (L=4-aminopy, py, 4-cynaopy), the higher the catalytic activity of the complexes. The results showed that the catalytic activity of the complexes were related with E_HOMO. The higher the E_HOMO- of the complexes, the closer the E_HOMO of the complexes to the E_LUMO of DAM, the stronger the interaction between them. The theoretical results were in accordance with the experimental data of the catalytic activity of the complexes. The calculation of the natural bond orbital and binding energy indicated, the weaker the interaction between the metal ion and the ligands, the easier the coordination of the complexes with DAM, and the higher the catalytic activity.The correlation between the electronic structures of the amine type of complexes and their catalytic activity was investigated. The complex catalyst PdL₂Cl₂ (L= n-propylamine,ethylenediamine,diethylamine,triethylamine,diphenylamine,triphenyla mine) have been studied. When electron donating alkyl was connected with N atom of amino, with the decrease of the E_HOMO of the complexes, the corresponding interaction between the complexes and DAM increased in order, the catalytic activity increased. Because of the steric hindrance of the ligand, the catalytic activity of diethylamine-type complexe was higher than the triethylamine-type complexe. When electron withdrawing phenyl was connected with N atom of amino, the higher the E_HOMO of the complexes, the stronger the interaction between the complexes and DAM, and the higher the catalytic activity.(2) The electronic structures and their catalytic hydrogenation performance of the model complexes with different central ionThe correlation between the electronic structures of the series of complexes MDAMH2 (M= Pd, Ni, Fe, Ru) and their catalytic activity was investigated by the model of MDAMH2. The computational results showed that the conversion of the reactant decreases with the increase of theΔε_L-H of complexes. The calculation of the natural bond orbital and binding energy and the frequency of the C=N indicated, the stability of the complexes and the binding force between the metal and DAM were closely related with their catalytic activity. The weaker the binding force between the metal ion and DAM, the higher the catalytic activity of the complexes.(3) Studies on thermodynamic properties of the catalytic hydrogenation of DAMThe computational results can be used to predict some thermodynamic properties of the complexes. It is found that the three reactions of catalytic hydrogenation of DAM were feasible.