硅烯及取代硅烯与饱和键插入反应的量子化学研究

Quantum Chemistry Study on the Insertion Reaction of Silylene and Its Substituted Species to Saturated Bond

用量子化学的密度泛函理论(DFT)在6-311G*水平上对硅烯及其取代物与甲烷的C-H键进行插入反应的势能面进行了系统地研究.用IRC方法对过渡态进行了验证.并用组态混合模型讨论了反应势垒(△E≠)和反应热(△H)与SiXY的单-三态激发能△Est的关系.我们发现,硅烯SiXY的△Est是控制反应的主要因素,取代基的电负性越大,取代基越多,π电子给予越强,SiXY的△Est就越大,插入反应的活化能就越大,放热就越小.

The potential energy surfaces for the insertion of silylene into C-H bond of methane were studied using density functional theory(DFT). All the stationary points were determined at the B3LYP/6 - 311G* level of the theory. The transition state both to the reactant and the product direction in the reaction paths was examined by using the intrinsic reaction coordinate (IRC). A configuration mixing model has been used to explain the barrier height and the reaction enthalpy. The results show that the single - triplet splitting AE, of the SiXY species plays an important role to predict its activity for the insertion reactions. The major conclusion is as follows: the mom strong the pi - donation is or the more electronegative the substituents are the larger the DeltaE(st) of SiXY, the higher the activation energy, and the smaller the exothermicity for the insertion of SiXY into saturated C-H bonds will be. In other words, it is the electronic factors, rather than the steric factors, that play a decisive role in determining the chemical reactivity of the silylene species.