关键词: 金属-乙烯配合物, 从头算, 密度泛函理论, 电子结构, 能量分解分析

Abstract: The geometries, electronic structures, and bonding energies of coinage metal-ethylene complexes LM-C₂H₄ (L=[N{(Me)C(Ph)N}₂]; M=Cu, Ag, Au) were investigated by Hartree-Fock, Møller- Plesset perturbation (MP2), second-order approximate coupled-cluster (CC2), and density functional theory (DFT) methods. The MP2, CC2, and DFT methods performed well in reproducing the experimental geometric features of LM-C₂H₄. The bonding in LM-C₂H₄ can be described as a synergistic combination of σ-donor and π-acceptor interactions between the LM and C₂H₄ π-system. Both σ-donor and π-acceptor contributions increased the C＝C bond length and decreased the C＝C bond strength by removing electron density from the bonding π orbital and increasing electron density in the anti-bonding π* orbital, respectively. The results of natural population analysis and energy decomposition analysis show that the LM→C₂H₄ back-donation contribution to the LM-C₂H₄ bonding is higher than that of the C₂H₄→LM donation, but this order is reversed in the M⁺-C₂H₄ systems. Therefore, it is not appropriate to use M⁺-C₂H₄ as a computational model for electronic structures studies of LM-C₂H₄. The effects of changing the metal on the structural and electronic properties, such as C＝C bond length, charge populations of C₂H₄, and LM-C₂H₄ interactions, were large. Compared with LCu and LAg, LAu had the strongest ability to accept and donate electrons. Consequently, it showed the maximum reduction in the π orbital electron density and increase in the π* orbital density. Therefore, activation of the C＝C bond by LAu was more effective than by LCu and LAg. However, the effects of electron donating or withdrawing ability of the auxiliary ligands on the above properties were small.

Key words: Metal-ethylene complex, Ab initio, Density functional theory, Electronic structure, Energy decomposition analysis