Kua Jeremy, Fletcher Matthew N, Iovine Peter M
Department of Chemistry, University of San Diego, 5998 Alcala Park, San Diego, CA 92110, USA.
J Phys Chem A. 2006 Jul 6;110(26):8158-66. doi: 10.1021/jp062055e.
Density functional theory (B3LYP//6-311+G) calculations including Poisson-Boltzmann implicit solvent and NMR were used to study the formation of a series of para-substituted triphenylboroxine.amine adducts with respect to their phenylboronic acid monomers and free amine in solution. Our calculations suggest that the intermediate prior to forming trimer.amine is a dimer.amine adduct. Formation of dimer.amine can proceed via two pathways. Electron-donating substituents favor dimerization of two monomers before addition of the amine, and electron-withdrawing substituents favor formation of a monomer.amine adduct before addition of the second monomer. We also find that pi-electron acceptors destabilize formation of the dimer and trimer with respect to its monomers. Electron-withdrawing substituents favor adduct formation. Adduct formation is enthalpically stabilized by increasing the polarity of the solvent but differential solubility of the monomer compared to trimer.amine also has an effect on the equilibrium constant.
采用密度泛函理论（B3LYP//6 - 311 + G）计算方法，结合泊松 - 玻尔兹曼隐式溶剂模型和核磁共振技术，研究了一系列对位取代的三苯基硼酸酯 - 胺加合物在溶液中相对于其苯基硼酸单体和游离胺的形成过程。我们的计算结果表明，在形成三聚体 - 胺之前的中间体是二聚体 - 胺加合物。二聚体 - 胺的形成可以通过两条途径进行。供电子取代基有利于在胺加成之前两个单体的二聚化，而吸电子取代基有利于在第二个单体加成之前形成单体 - 胺加合物。我们还发现，π电子受体相对于其单体而言会使二聚体和三聚体的形成不稳定。吸电子取代基有利于加合物的形成。通过增加溶剂的极性，加合物的形成在焓上得到稳定，但单体与三聚体 - 胺的溶解度差异也对平衡常数有影响。
