School of Chemistry and Chemical Engineering, Henan Key Laboratory of Boron Chemistry and Advanced Energy Materials , Henan Normal University , Xinxiang , Henan 453007 , China.
Department of Chemistry , Brown University , Providence , Rhode Island 02912 , United States.
J Am Chem Soc. 2018 May 30;140(21):6718-6726. doi: 10.1021/jacs.8b03785. Epub 2018 May 16.
Boron compounds are well-known electrophiles. Much less known are their nucleophilic properties. By recognition of the nucleophilicity of the B-H bond, the formation mechanism of octahydrotriborate (BH) was elucidated on the bases of both experimental and computational investigations. Two possible routes from the reaction of BH and THF·BH to BH were proposed, both involving the BH and BH intermediates. The two pathways consist of a set of complicated intermediates, which can convert to each other reversibly at room temperature and can be represented by a reaction circle. Only under reflux can the BH and BH intermediates be converted to BH and BH(H) via a high energy barrier, from which H elimination occurs to yield the BH final product. The formation of BH from THF·BH by nucleophilic substitution of the B-H bond was captured and identified, and the reaction of BH with BH to produce BH was confirmed experimentally. On the bases of the formation mechanisms of BH, we have developed a facile synthetic method for MBH (M = Li and Na) in high yields by directly reacting the corresponding MBH salts with THF·BH. In the new synthetic method for MBH, no electron carriers are needed, allowing convenient preparation of MBH in large scales and paving the way for their wide applications.
硼化合物是众所周知的亲电试剂。但人们对它们的亲核性质知之甚少。通过识别 B-H 键的亲核性，我们在实验和计算研究的基础上阐明了八氢三硼酸（BH）的形成机制。根据 BH 和 THF·BH 反应生成 BH 的两种可能途径，提出了两种可能的途径，都涉及 BH 和 BH 中间体。这两条途径包含了一系列复杂的中间体，它们在室温下可以相互可逆转化，可以用一个反应循环来表示。只有在回流条件下，BH 和 BH 中间体才能通过高能量垒转化为 BH 和 BH(H)，然后发生 H 消除反应，生成 BH 最终产物。通过 B-H 键的亲核取代反应，捕获并鉴定了从 THF·BH 生成 BH 的反应，并且通过实验证实了 BH 与 BH 反应生成 BH 的反应。基于 BH 的形成机制，我们开发了一种简便的合成方法，可以通过直接将相应的 MBH 盐与 THF·BH 反应，以高产率得到 MBH（M = Li 和 Na）。在这种新的 MBH 合成方法中，不需要电子载体，允许在大规模条件下方便地制备 MBH，为其广泛应用铺平了道路。
