BF_3活化高锰酸氧化丙烯酸反应机理的密度泛函研究

Density functional study on the mechanism of BF_3-activated oxidation of alkenes by MnO_4^-

用量子化学密度泛函理论(DFT)的B3LYP方法对高锰酸根离子与丙烯酸的环加成反应机理进行了系统研究,全参数优化了反应势能面上各驻点的几何构型、振动频率和能量.计算结果表明:反应有两个竞争通道,即[2+3]反应通道和[2+2]反应通道,其中[2+3]通道比[2+2]通道的反应势垒降低了183.89kJ/mol,并通过在高锰酸根的氧原子上配位一个或两个BF3分子来研究BF3分子对反应体系的活化效应,结合两个BF3分子使得[2+3]通道的反应势垒降低为23.97kJ/mol,则有利于反应按该通道进行,然而[2+2]通道的反应势垒仍较高(>195kJ/mol).这进一步表明该反应体系中加入一定量BF3能提高高锰酸氧化烯烃双键的化学活性.

A computational study of the Cycloaddition reactions of permanganate ion with acrylic acid is presented.The reaction proceeds through two competing channels：[2＋3 ]and [2＋2] pathway.The accelerating effect for the reaction systems was investigated by explicit coordination of the BF3 molecules to the oxygen atoms in the permanganate ion.The barriers for the [2＋3]pathway become systematically lower as more BF3 molecules are added（from 36.44 kJ/mol for no BF3 molecules to 23.97 kJ/mol for two BF3 molecules）.The reactions are able to occur readily at low temperatures.By contrast,the reaction barriers for the[2＋2] pathway remain high（195 kJ/mol）.These results suggest that the BF3 molecule helps to enhance the chemical reactivity of the MnO4-toward olefins.The computational results are in reasonable agreement with experimental results.