C_(60)与硅烯环加成反应机理的理论研究

Theoretical Studies on the Mechanism Cycloaddition Reaction of Silylene with C_(60)

用半经验AM 1法研究了C60 与单态硅烯环加成反应机理 .经Berny梯度法优化得到反应的过渡态 ,并进行了振动分析确认 .计算结果表明 :硅烯在C60 的 6 6键上的加成反应分两步 ,第一步反应物生成中间配合物 ,无势垒 ;第二步由中间配合物经过渡态变为产物 .6 5键上的加成反应分三步 ,第一步由反应物生成中间配合物 ,第二步由中间配合物经过渡态I得到闭环结构的中间体 ,第三步由中间体经过渡态Ⅱ形成产物 .6 6键加成反应的活化势垒较低 ,从反应机理和动力学角度解释了 6 6键加成优于 6 5键加成的原因 .

The cycloaddition reaction of silylene(SiH_2) and C_60 have been studied by using the semi-empiri- cal method AM1, a reasonable mechanism of the reaction has been suggested. All the geometry of the sta- tionary points on the reaction path have been optimized by energy gradient technique and the transition states were characterized by vibration frequency analysis. The calculation results show that the reaction mechanism is different between 6-6 and 6-5 bond addition. The 6-6 bond cycloaddition reaction proceedvia two steps: (1) Silylene and C_60 form an intermediate complex; (2) The closed isomer of C_60SiH_2 is formedvia TS from intermediate complex. After being corrected by zero-point energies the barriers is 0.45 kJ·mol^-1. While the 6-5 cycloaddition reaction is of three steps: (1) An intermediate complex is formed from the reactants C_60 and SiH_2 with no barrier. (2) The closed intermediate is formedvia TS(Ⅰ). After being corrected by zero-point energies the barriers is 9.19 kJ·mol^-1. (3) The opened isomer of C_60SiH_2 is producedvia TS(Ⅱ) with the barrier of 4.33 kJ·mol^-1. The reasons that silylene cycloaddition should take place across 6-6 bond rather than 6-5 bond of C_60 are explained from the reaction mechanism and kinetic factors.