PH_2X与五元杂环体系磷键相互作用的理论研究

Theoretical Study of Pnicogen Bonding Interactions between PH_2X and Five-membered Heterocycles

用MP2/aug-cc-pVDZ方法计算了PH2X(X=H,F,Cl,Br)与五元杂环化合物(吡咯、呋喃、噻吩)的相互作用,经完全均衡校正法校正基组重叠误差.在MP2/aug-cc-pVDZ优化基础上采用Gaussian 03程序包中的NBO程序计算了二级微扰稳定化能(ΔE2),并运用AIM 2000程序对其AIM性质进行了计算.为了进一步加强对该类相互作用的认识,应用约化密度梯度(RDG)填色等值面图和电子密度差图对代表性的体系进行了图形化分析.研究表明:PH3与三个五元杂环化合物形成的是P—H…π氢键相互作用;PH2X(X=F,Cl,Br)与五元杂环化合物形成磷键相互作用,这些磷键体系存在π型和n型两种形式的磷键相互作用,前者形成复合物的稳定性高于后者,并且相互作用大小与磷原子到杂环质心的矢量和P—X方向矢量的夹角密切相关.作为比较,我们对PCl3与这三种杂环化合物之间的相互作用也进行了研究,结果发现,PCl3分子中沿Cl—P键的P端出现了三个正的静电势区域或称作"σ-hole",因此其与杂环化合物形成的是分子间多磷键复合物.AIM拓扑分析表明磷键相互作用的本质属于闭壳层静电相互作用,且电子密度与复合物稳定性呈正相关.RDG图形化分析揭示了磷键相互作用所在的空间位置以及相对强度.DDF分析表明,磷键相互作用的存在使磷原子端基的电子密度减少,而沿着P—X轴以及五元杂环分子的电子密度增加,从而直观地体现了形成复合物后电子密度的重排情况.

Intermolecular interactions between PH2X （X=H, F, C1, Br） and five-member heterocyclic compounds （pyrrole, furan, thiophene） were calculated by using MP2/aug-cc-pVDZ quantum chemical method, and the interaction energies were corrected with BSSE （basis set superposition error） by complete counterpoise correction method. On the basis of MP2/aug-cc-pVDZ optimized geometries, the second-order perturbation stabilization energies （AE2） and AIM properties were calculated using the NBO （natural bond orbital） program in Gaussian 03 and AIM 2000 program, respectively. In order to further understand this type of interaction, graphical analyses for representative systems were performed using the reduced density gradient （RDG） color-filled isosurface map and the electronic density difference map. It has been showed that the P…π hydrogen bonding interaction is formed between PH3 and three five-member heterocyclic compounds, and the pnicogen bonding interactions between PH2X （X=F, C1, Br） and five-member heterocyclic compounds. There exist two types of pnicogen bonding interactions （π- and n-types） in these complexes, and the stabilities of the n-type pnicogen bonded complexes are stronger than those of the n-type ones. Moreover, the interaction energies have been found to correlate closely with the angle between P--X vector and the direction vector of P atom to the heterocyclic centroid. For comparison, inter- molecular interactions between PC13 and the three kinds of heterocyclic compounds were also studied, It has been showed that three positive electrostatic potential areas （or ＂a-hole＂） are presented at phosphorus atom end along the C1--P bond in PC13 molecule, so the complexes with multi-pnicogen-bonding can be formed between PC13 and the heterocyclic compounds. Through atom in molecule （AIM） analysis, it has been disclosed that the nature of all the pnicogen bonding interactions be- longs to the closed-shell electrostatic interactions, and the stabilities of the complexes are correlated positively with the elec- tron densities in the bond critical points （BCPs）. RDG graphical analyses are performed to visualize the positions and strengths of the pnicogen bonding. DDF analyses are also done, and indicating that electron density is reduced at phosphorusatom end and increased around the P--X axis and five-member heterocyclic molecule because of the pnicogen bonding in- teraction, thus the underlying rearrangement of the electron densities is intuitively reflected.