Lewis碱稳定的硼代苯与亲二烯体的Diels-Alder反应的理论研究

Theoretical Study of the Diels-Alder Reactions of Lewis Base-Stabilized Borabenzenes with Dienophiles

采用密度泛函理论方法在B3LYP/6-31G(d)水平上研究了Lewis碱稳定的硼代苯与一些亲二烯体的两种可能的Diels-Alder反应的微观机理和势能剖面,并研究了反应的溶剂效应和取代基效应.计算结果表明,一部分反应以直接的近同步的协同方式进行,而在另一部分反应中,两个反应物分子先形成分子间复合物,然后再经过协同的过渡态生成产物.与气相中相比,二氯甲烷溶剂使所研究的大部分反应的活化能垒有所增加.在乙炔或乙烯分子中分别引入吸电子基团CO2Me或CN能显著降低反应的活化能垒.形成一个C—B键的杂Diels-Alder反应都比相应的Diels-Alder反应在热力学和动力学上容易进行,这与实验结果一致.

Density functional theory （DFT） calculations at the B3LYP/6-31 G （d） level of theory were employed to study the mechanism and the potential energy surface of Diels-Alder reactions between Lewis base stabilized borabenzene and dienophiles. The solvent effect and substituent effect were also considered. The results indicate that some of the reactions take place in a simple concerted way, while other reactions will form an intermolecular complex first and then proceed through a concerted transition state to obtain final products. The studies on the solvent and substituent effects reveal that the CHECl2 solvent will elevate the activation barriers, while CO2 Me or CN groups on C atom of acetylene or ethylene may lower the activation barriers considerably. The Diels-Alder reactions forming one C-B bond and one C-C bond are always more favorable than the corresponding Diels-Alder reactions forming two C-C bonds, both thermodynamically and kinetically, which is in agreement with experimental observation.