Structural changes, P-P bond energies, and homolytic dissociation enthalpies of substituted diphosphines from quantum mechanical calculations.
Structural changes, P-P bond energies, and homolytic dissociation enthalpies of substituted diphosphines from quantum mechanical calculations.
复制标题
根据量子力学计算得出取代二膦的结构变化、P-P 键能和均解离解焓。
作者：
K. B. Borisenko;D. Rankin
用理论量子化学方法在HF/3- 21g *、B3LYP/3- 21g *和MP2/6-31+G*水平上预测了二膦化合物P(2)[CH(SiH(3))(2)](4)、P(2)[SiH(CH(3))(2)](4)、P(2)[Si(CH(3))(3)](4)和P(2)[Si(CH(3))(3)](2)、P[SiH(CH(3))(2)]、P[SiH(CH(3))(2)]、P[Si(CH(3))(3)](2)的分子结构。所有结构的构象分析发现，具有C(2)对称的二膦的间扭构象是最稳定的。最稳定的磷酸基构象也被发现具有C(2)对称性。解离时的结构变化允许释放一些储存在取代基中的能量，因此有助于P-P键解离能的降低。在B3LYP/3- 21g *水平上，所研究化合物的P-P键解离焓从-11.4 kJ mol(-1) (P(2)[C(SiH(3))（3)](4)）到179.0 kJ mol(-1) (P(2)[SiH(CH(3))（2)](4)）不等。MP2/6-31+G*计算预测它们在52.8-207.9 kJ mol（-1）的范围内。所有的值都对基集叠加误差进行了校正。采用弹簧连接柔性取代基的力学类比定义的P-P键能变化较小，在B3LYP/3-21G水平上在191.3 ~ 222.6 kJ mol（-1）之间，在MP2/6-31+G*水平上在225.6 ~ 290.4 kJ mol（-1）之间。它的平均值可以用来从结构弛豫的能量学中估计键的离解能。
The molecular structures of the diphosphines P(2)[CH(SiH(3))(2)](4), P(2)[C(SiH(3))(3)](4), P(2)[SiH(CH(3))(2)](4), and P(2)[Si(CH(3))(3)](4) and the corresponding radicals P[CH(SiH(3))(2)](2), P[C(SiH(3))(3)](2), P[SiH(CH(3))(2)](2), and P[Si(CH(3))(3)](2) were predicted by theoretical quantum chemical calculations at the HF/3-21G*, B3LYP/3-21G*, and MP2/6-31+G* levels. The conformational analyses of all structures found the gauche conformers of the diphosphines with C(2) symmetry to be the most stable. The most stable conformers of the phosphido radicals were also found to possess C(2) symmetry. The structural changes upon dissociation allow the release of some of the energy stored in the substituents and therefore contribute to the decrease of the P-P bond dissociation energy. The P-P bond dissociation enthalpies at 298 K in the compounds studied were calculated to vary from -11.4 kJ mol(-1) (P(2)[C(SiH(3))(3)](4)) to 179.0 kJ mol(-1) (P(2)[SiH(CH(3))(2)](4)) at the B3LYP/3-21G* level. The MP2/6-31+G* calculations predict them to be in the range of 52.8-207.9 kJ mol(-1). All the values are corrected for basis set superposition error. The P-P bond energy defined by applying a mechanical analogy of the flexible substituents connected by a spring shows less variation, between 191.3 and 222.6 kJ mol(-1) at the B3LYP/3-21G level and between 225.6 and 290.4 kJ mol(-1) at the MP2/6-31+G* level. Its average value can be used to estimate bond dissociation energies from the energetics of structural relaxation.