锗硅烯与CH_3OH加成反应机理及区域选择性

Mechanism and Regioselectivity of Addition Reactions of CH_3OH to Germasilenes

采用密度泛函理论方法,在B3LYP/6-311++G(d,p)水平,研究了几种锗硅烯与CH3OH的加成反应的微观机理和势能剖面,分析了锗硅烯中Si=Ge双键的极性对加成反应区域选择性的影响.研究结果表明,锗硅烯可分别与CH3OH的单聚体或二聚体发生加成反应.所有加成反应均从初始亲核或亲电复合物的形成开始.母体锗硅烯H2Si=Ge H2与CH3OH二聚体的加成反应比其与CH3OH单聚体的相应反应在动力学上更容易些,但在其它锗硅烯与CH3OH的反应中情况则相反.用Ph或Si Me3基团取代H2Si=Ge H2中的H原子在动力学上使反应变得不利且Si Me3基团的影响更显著.加成反应的区域选择性与锗硅烯中Si=Ge双键的极性以及Si-O(Ge-H)和Ge-O(Si-H)键的相对强弱都有关.

Density functional theory（DFT） calculations of the reaction mechanisms and potential energy surfaces for the addition reactions of CH3 OH to several germasilenes were performed at the B3LYP/6-311＋＋G（d,p） level. The effect of the polarity of the Si=Ge double bond in germasilenes on the regioselectivity of the addition reactions was also investigated. The results indicate that germasilenes can react with a monomer or dimer of CH3 OH. All reactions start with formation of nucleophilic or electrophilic complexes. The dimer of CH3 OH adds to H2Si=Ge H2 kinetically more easily than the monomer. However, the situation is generally the opposite for substituted germasilenes. There is a kinetic disadvantage of substituting phenyl（Ph）or Si Me3 groups for H atoms in H2Si=Ge H2 in the addition reactions, and the effect of the Si Me3 group is more remarkable than that of the Ph substituent. Both the polarity of the Si=Ge double bond and the strength of the Si-O（Ge-H） and Ge-O（Si-H） bonds affect the regioselectivity of the addition reactions.