硅烯与甲醛环加成反应的理论研究

Theoretical Study on the Cycloaddition Reaction of Silylene and Formaldehyde

本文用RHF/6-31G^(?)解析梯度方法研究了单重态硅烯与甲醛环加成反应的机理,用二级微扰方法对各构型的能量进行了相关能校正,并用统计热力学方法和过渡态理论计算了该反应在不同温度下的热力学函数的变化和动力学性质.结果表明,此反应历程由两步组成:1)硅烯与甲醛生成—中间配合物,是一无势垒的放热反应,2)中间配合物异构化为产物,此步势垒经零点能校正后只有51.4kJ·mol^(-1)(MP2/6-31G^(?)∥6-31G^(?));从热力学和动力学的综合角度考虑,该反应在300～400K温度下进行为宜,如此,反应既有较大的自发趋势和平衡常数,又具有较快的反应速率.

The mechanism of the cycloaddition reaction of singlet silylene with formaldehyde has been studied by RHF/6 - 31G* gradient method. The electron correlation energies of all the structures are calculated by using second - order Moller - Plesset perturbation theory(MP2) . We have also calculated the changes of thermodynamic functions and the quality of kinetic properties for this reaction at different temperatures by using statistical thermodynamics method and transition - state theory. The results show that this reaction proceeds in two steps: 1) silylene and formaldehyde form an intermediate complex, which is a kind of exothermal reaction with no barrier; 2) the intermediate complex isomerizes to sive the product. The barrier for the second step is 51.4kJ·mol-1 at MP2/6 - 31G* //6 - 31G* level (with zero - point energies correction). In view of dynamics and thermodynamics, it is between 300-400K that the reaction will have not only larger spontaneous tendency and equilibrium constant but also quicker reaction rate.