9-硅蒽和9-锗蒽与烯烃杂Diels-Alder反应的理论研究

采用密度泛函理论方法在B3LYP/6-311G**水平研究了9-硅蒽和9-锗蒽与烯烃的杂Diels-Alder反应的微观机理、势能剖面,考察取代基对反应势能剖面的影响.计算结果表明,所研究反应均以协同非同步的方式进行,且Si(Ge)—C键总是先于C—C键形成.乙烯分子中C原子上的苯基取代基在热力学上对反应不利,但在动力学上的影响取决于产物中苯基与Si(Ge)原子之间的相对位置.9-硅(锗)蒽分子中Si(Ge)原子上的2,4,6-三甲基苯基取代基在热力学和动力学上均对反应不利.

Theoretical Study on the Hetero-Diels-Alder Reactions of 9-silaanthracene and 9-germaanthracene with Alkenes

The mechanism and potential energy surface of the hetero-Diels-Alder reactions of 9-silaanthracene or 9-germaanthracene with alkenes were investigated using density functional theory( DFT) at the B3LYP /6-311G**level and the influences of some substituents on the potential energy surface were explored. The obtained results were compared with those of the corresponding reactions of silabenzene or germabenzene. The results show that all reactions occur in a concerted but nonsynchronous way and the formation of Si( Ge) —C bond always keeps ahead the formation of C—C bond. The phenyl group at C atom of ethylene molecules is not in favor of the hetero-Diels-Alder reactions thermodynamically,however,its influence on the kinetic properties of the reaction are determined by the relative position of phenyl with Si( Ge) atom in products. The mesityl substituent at Si( Ge) atom of 9-silaanthracene or 9-germaanthracene molecules has an unfavorable effect on the reactions both thermodynamically and kinetically.