Department Chemie & Catalysis Research Center, Technische Universität München, 85747 Garching, Germany.
Chemistry. 2012 Jul 16;18(29):9106-16. doi: 10.1002/chem.201104015. Epub 2012 Jun 12.
The initial steps of the thermal decomposition of silanes in the gas phase were examined by DFT-B3LYP calculations, with particular attention being paid to the way in which the reactivity pattern changes with the degree of branching of the silane. Besides the established pathways-1,2-hydrogen shift, H(2) elimination, and homolytic dissociation-1,3-hydrogen shift was also explored as an initial reaction step which leads to disilene structures. Subsequent silylene insertion and initial steps of radical chain reactions were also studied. To estimate the energetic changes with temperature, various reaction free energies and the corresponding activation free energies up to 650 °C were calculated. Accordingly, the leading reaction channel at room temperature is 1,2-hydrogen shift with subsequent silylene insertion; for higher degrees of branching, competing pathways (homolytic dissociation, 1,3-hydrogen shift, and radical polymerization) gain in relative importance. At high temperatures, the rate-determining step changes to homolytic dissociation, and thereby the apparent rates of decomposition become dependent on the degree of branching.
通过 DFT-B3LYP 计算研究了硅烷在气相中的热分解的初始步骤，特别关注随着硅烷支化程度的变化，反应性模式的变化方式。除了已建立的途径-1,2-氢转移、H2 消除和均裂解离-1,3-氢转移之外，还探索了 1,3-氢转移作为导致二硅烯结构的初始反应步骤。随后还研究了硅烯插入和自由基链式反应的初始步骤。为了估计随温度的能量变化，计算了各种反应自由能和相应的激活自由能，最高可达 650°C。因此，在室温下的主要反应通道是 1,2-氢转移，随后是硅烯插入；对于更高的支化程度，竞争途径（均裂解离、1,3-氢转移和自由基聚合）的相对重要性增加。在高温下，速率决定步骤变为均裂解离，因此分解的表观速率取决于支化程度。
