Islam Shahidul M, Hollett Joshua W, Poirier Raymond A
Department of Chemistry, Memorial University of Newfoundland, St. John's, Newfoundland, Canada A1B 3X7.
J Phys Chem A. 2007 Jan 25;111(3):526-40. doi: 10.1021/jp066524o.
Ab initio calculations were carried out for the reactions of silane and halosilanes (SiH3X, X=H, Cl, Br, I) with HCN. Geometries of the reactants, transition states, intermediates and products were optimized at HF, MP2, and B3LYP levels of theory using the 6-31G(d) and 6-31G(d,p) basis sets. Energies were also obtained using G3MP2 and G3B3 levels of theory. Intrinsic reaction coordinate (IRC) calculations were performed to characterize the transition states on the potential energy surface. It was found that HCN can react with silane and halosilanes via three different mechanisms. One involves HX elimination by a one-step pathway producing SiH3CN. The second mechanism consists of H2 elimination, producing SiH2XCN via a one-step pathway or three multiple-step pathways. The third mechanism involves dissociation of SiH3X to various products, which can then react with HCN. Activation energies, enthalpies, and free energies of activation along with the thermodynamic properties (DeltaE, DeltaH, and DeltaG) of each reaction pathway were calculated. The reaction of SiH3X with HCN produce different products depending on substituent X. We have found that the standard 6-31G(d) bromine basis set gave results which were in better agreement with the G3MP2 results than for the Binning-Curtiss basis set. Computed heats of formation (DeltaHf) for SiH3CN, SiH3NC, SiH2ClCN, SiH2BrCN, SiH2ICN, SiHCl, SiHBr, and SiHI were found to be 133.5, 150.8, -34.4, 23.6, 102.4, 48.7, 127.1, and 179.8 kJ mol-1, respectively. From enthalpies calculated at G3MP2, we predict that the DeltaHf for SiH2 to be 262.8 kJ mol-1 compared to the experimental value of 273.8+/-4.2 kJ mol-1.
对硅烷和卤代硅烷（SiH3X，X = H、Cl、Br、I）与HCN的反应进行了从头算计算。使用6 - 31G(d)和6 - 31G(d,p)基组，在HF、MP2和B3LYP理论水平上对反应物、过渡态、中间体和产物的几何结构进行了优化。还使用G3MP2和G3B3理论水平获得了能量。进行了内禀反应坐标（IRC）计算以表征势能面上的过渡态。发现HCN可通过三种不同机制与硅烷和卤代硅烷反应。一种是通过一步途径消除HX生成SiH3CN。第二种机制是消除H2，通过一步途径或三步多步途径生成SiH2XCN。第三种机制涉及SiH3X分解为各种产物，然后这些产物可与HCN反应。计算了每个反应途径的活化能、焓和活化自由能以及热力学性质（ΔE、ΔH和ΔG）。SiH3X与HCN的反应根据取代基X产生不同产物。我们发现标准的6 - 31G(d)溴基组给出的结果与G3MP2结果的一致性比Binning - Curtiss基组更好。计算得到的SiH3CN、SiH3NC、SiH2ClCN、SiH2BrCN、SiH2ICN、SiHCl、SiHBr和SiHI的生成热（ΔHf）分别为133.5、150.8、 - 34.4、23.6、102.4、48.7、127.1和179.8 kJ mol-1。根据G3MP2计算的焓，我们预测SiH2的ΔHf为262.8 kJ mol-1，而实验值为273.8±4.2 kJ mol-1。
