GeX_2(X=F,Cl)与甲醛环加成反应机理的理论研究

Theoretical Study on Mechanism of Cycloaddition Reaction of GeX_2(X=F,Cl) with Formaldehyde

在从头算方法HF/6311+G水平上研究了单重态GeX2(X=F,Cl)与甲醛的环加成反应,找到了反应的中间配合物和过渡态,并在MP4(SDTQ)/6311+G计算水平上进一步进行单点算,对得到的复合物以振动频率确认其驻点性质(过渡态和稳定态),讨论了其反应机理.结果表明,二氟锗烯与甲醛的环加成反应分两步进行,第一步生成中间配合物,是一个无势垒的放热反应;第二步是中间配合物异构化为产物%D二氟锗杂环氧甲烷,计算的反应势垒为196.4kJ/mol,是整个反应发生的控速步骤.而在二氯锗烯与甲醛环加成反应中,对应的控速步骤的能垒仅为125.7kJ/mol.与二氟硅烯与甲醛环加成反应相比,二氟锗烯与甲醛的环加成反应速率要慢一些,而二氯锗烯与甲醛环加成反应速率则与其相当.

The mechanisms of the cycloaddition reaction of singlet GeX2 （ X = F, Cl） with formaldehyde was studied employing the HF/6-311 ＋ G^＊ theory. The electron-correlation corrections have been further considered by the fourth-order Moller-Plesset perturbation theory （MP4SDTQ/6-311 ＋ G^＊ ）. The results show that this reaction proceeds in two steps： ① Difluorogemylene and formaldehyde form an intermediate complex, which is a barrierless exothermal reaction;②the intermediate complex isomerizes to form the product, which is a rate-control step in the whole reaction. In the second step, the calculated barrier heights are 216.7 and 196.4 kJ/mol before and after considering electron-correlation effects. Compared with that of the cycloaddition reaction of difluorosilylene with formaldehyde, the cycloaddition reaction of difluorogemylene with formaldehyde is relatively slow, whereas the cycloaddition reaction of dichlorogemylene with formaldehyde can be comparable in speed.