R·BH3中B-H键与酚类物质的反应研究

摘要

Understanding the reactivity of borane is a challenging task since the complex R·BH3can behave as both Lewis acid and Lewis base. The deficiency in valence electrons in B always makes such type compounds act as Lewis acid. On the other hand,the electronegativity of boron(2.0) is less than that of hydrogen(2.1),thus the hydrogen of B is hydridic,which can act as Lewis base. The reactivi-ty of B-H bond in R·BH3(R=THF, DMA, NH3) towards phenols has been studied systematically. The experiment results have shown that all hydridic hydrogens in B-H of R·BH3(R=THF, DMA) can react with the protic hydrogens in O-H of phenol(ROH) to produce H2and B(OR)3borate.With the base strength decreased,NH3> DMA > THF, the relative reactivity of hydridic hydrogen of B-H increased in the sequence of NH3·BH3< DMA·BH3< THF·BH3. According to the experiment results and the DFT calculation, we proposed a four-step mechanism for the reaction of R·BH3and phenols. The characteristics of the ligands (THF, NH3, DMA) of borane and the B-Hδ-…δ+H-O dihydrogen bonds play important roles in the reactions.%硼烷化合物既能表现路易斯酸性,因分子B-H键中的氢带负电荷,又可表现出路易斯碱性.本文系统研究了R·BH3(R=THF,DMA,NH3)与酚类物质在常温常压无催化剂条件下的反应,发现R·BH3(R=THF, DMA)硼烷中与B相连的负电性氢能够全部与酚中与氧相连的正电性氢发生反应,生成含BO3的硼酸酯和氢气,但NH3·BH3却不与酚发生反应.DMA ·BH3与间苯二酚反应生成聚合物.根据实验结果,我们推测随着与硼配位的路易斯碱的配位能力/碱性减弱(NH3> DMA > THF),B-H活性增强,即R·BH3与酚类物质的反应程度按照NH3·BH3< DMA·BH3< THF·BH3顺序依次增强.结合实验和理论计算发现,硼烷与酚的反应是分四步进行的,反应第一步的主要影响因素是与硼配位的配体离去的难易,而B-Hδ-…δ+H-O双氢键在第二步到第四步反应中发挥了重要作用.配体的性质及B-Hδ-…δ+H-O双氢键在反应中发挥着重要作用.