醚溶液中烯烃硼氢化反应机理的理论模拟

在B₃LYP/6-31G^*水平上以二甲醚(Me₂O)模拟四氢呋喃(THF)对烯烃在THF溶液中硼氢化反应的机理进行了研究.计算结果发现,烯烃通过类似SN₂的交换过程从醚与BH₃构成的配合物获得BH₃结合成π配合物中间体,这一交换是整个硼氢化反应的决速步骤.

A Theoretical Simulation of Hydroboration of Alkenes with BH3 in Ether Media

The reaction of the monomeric BH₃ with alkenes in ether media has been examined by using B3LYP, a hybrid density functional method, with 631G^* basis set. Calculations of various possible species involveDIn the hydroboration process, including the complexes of borane (BH₃) with dimethyl ether, ethylene, propene, 1-butene, trans-2-butene, cis-2-butene, 2-methylpropene, 2-methyl 2-butene and 2,3-dimethyl-2-butene as well as the reactants and transition states of the corresponding hydroboration have been performed. The zero point energies(ZPE) and thermal analyses were computed at the same level. Based on the calculations, the prior formation of a three center π-complex intermediate of BH₃ with the respective alkene is predicted and the overall reaction rate was determined. For the formation of the π-complex intermediates, two extreme pathways, i.e . the S_N1 and S_N2-like manner, have been compared, with the latter one more preferentially in terms of the activation barrier by 25²8 kJ/mol endothermically.