Dispersion Force Effects on the Dissociation of "Jack-in-the-Box" Diphosphanes and Diarsanes
Dispersion Force Effects on the Dissociation of "Jack-in-the-Box" Diphosphanes and Diarsanes
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DOI：
10.1021/acs.organomet.5b00254
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发表时间：
2015-05-25
期刊：
影响因子：
2.8
通讯作者：
Power, Philip P.
中科院分区：
文献类型：
--
作者：
Guo, Jing-Dong;Nagase, Shigeru;Power, Philip P.
用杂化密度泛函理论（DFT）在B3 PW 91上对空间位阻的二膦和二砷烷[：E{CH（SiMe 3）（2）}（2）]（2）（E = P或As）和[：E{N（SiMe 3）（2）}（2）]（2）（E = P或As）解离成：E{CH（SiMe 3）（2）}（2）或：E{N（SiMe 3）（2）}（2）自由基单体进行了计算，P和As采用6-311+G（d）基组，其它原子采用6- 31 G（d，p）基组.采用色散修正B3 PW 91-D3方法对结构进行了优化，以估算色散力效应。计算结果与实验数据吻合较好。在不进行色散校正的情况下，磷和砷四烷基化合物的负离解能分别为-10.3和-6.5 kcal mol（-1），表明自由基单体更稳定。相反，色散力效应的引入提供了+37.6和+37.1 kcal mol（-1）的高正离解能，有利于二聚体结构。对于四酰胺基取代的二聚体计算的解离能（无色散）也是负的，但在用D3色散项优化后变为+29.3和+32.5千卡莫里的正值。与早期的计算相反，早期的计算表明四烷基二聚体内累积的应变能的释放是解离成单体的驱动力（即，“Jack-in-the-Box”分子模型），目前的计算表明，分散力吸引相互作用超过配体弛豫和稳定的二聚体结构。包括色散效应的单点MP2（二阶Moller-Plesset微扰理论）计算得出四烷基物质的离解能为30.4和30.8 kcal mol（-1），这表明将D3色散项添加到B3 PW 91泛函中可能会高估这些力7-8 kcal mol（-1）。结果表明，色散力的平衡和熵效应是决定解离平衡的主要因素。
The dissociation of the sterically encumbered diphosphanes and diarsanes [:E{CH(SiMe3)(2)}(2)](2) (E = P or As) and [:E{N(SiMe3)(2)}(2)](2) (E = P or As) into :E{CH(SiMe3)(2)}(2) or :E{N(SiMe3)(2)}(2) radical monomers was studied computationally using hybrid density functional theory (DFT) at the B3PW91 with the 6-311+G(d) basis set for P and As, and the 6-31G(d,p) basis set for other atoms. The structures were reoptirnized with the dispersion corrected B3PW91-D3 method to estimate dispersion force effects. The calculations reproduced the experimental structural data for the tetraalkyls with good accuracy. Without the dispersion correction, negative dissociation energies of -10.3 and -6.5 kcal mol(-1) were calculated for the phosphorus and arsenic tetraalkyls, indicating that the radical monomers are more stable. In contrast, the incorporation of dispersion force effects afforded high, positive dissociation energies of +37.6 and +37.1 kcal mol(-1) that favored dimeric structures. The dissociation energies (without dispersion) calculated for the tetraamido-substituted dimer are also negative, but changed to positive values of +29.3 and +32.5 kcal mori upon optimization with the D3 dispersion term. In contrast to earlier calculations, which indicated that the release of accumulated strain energy within the tetraalkyl dimers was the driving force for dissociation to monomers (i.e., the "Jack-in-the-Box" molecular model), the current calculations show that dispersion force attractive interactions exceed those of ligand relaxation and stabilize the dimeric structures. Single-point MP2 (second-order Moller-Plesset perturbation theory) calculations including dispersion effects afforded dissociation energies of 30.4 and 30.8 kcal mol(-1) for the tetraalkyl species, suggesting that the addition of the D3 dispersion term to the B3PW91 functional may overestimate such forces by 7-8 kcal mol(-1). It is concluded that the balance of dispersion forces and entropic effects are the major determinants of the dissociation equilibria.