Xi-Meng Chen,^†,⊥ Nana Ma,^†,⊥ Qian-Fan Zhang,^‡ Jin Wang,^† Xiaoge Feng†, Changgeng Wei,^† Lai-Sheng Wang,*^,‡ Jie Zhang,*^{, †} and Xuenian Chen*^,†

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 (B₃H₈⁻) was elucidated on the bases of both experimental and computational investigations. Two possible routes from the reaction of BH₄⁻ and THF•BH₃ to B₃H₈⁻ were proposed, both involving the B₂H₆ and BH₄⁻ 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 B₂H₆ and BH₄⁻  intermediates be converted to B₂H₅⁻ and BH₃(H₂) via a high energy barrier, from which H₂ elimination occurs to yield the B₃H₈⁻ final product. The formation of B₂H₆ from THF•BH₃  by nucleophilic substitution of the B−H bond was captured and identified, and the reaction of B₂H₆ with BH₄^– to produce B₃H₈⁻ was confirmed experimentally. On the bases of the two formation mechanisms of B₃H₈^–, we have developed a facile synthetic method for MB₃H₈ (M = Li and Na) in high yields by directly reacting the corresponding MBH₄ salts with THF•BH₃. In the new synthetic method for MB₃H₈, no electron carriers are needed, allowing convenient preparation of MB₃H₈ in large scales and paving the way for their wide applications.
该论文第一作者为陈学年老师的博士生陈西孟同学和麻娜娜老师，第一单位为河南师范大学。原文链接为https://pubs.acs.org/doi/10.1021/jacs.8b03785