Facile Synthesis of Unsolvated Alkali Metal Octahydrotriborate Salts MB 3 H 8 (M=K, Rb, and Cs), Mechanisms of Formation, and the Crystal Structure of KB 3 H 8

• Published in: Angewandte Chemie International Edition Vol. 58; no. 9; pp. 2720 - 2724
• Main Authors: Chen, Xi-Meng, Ma, Nana, Liu, Xin-Ran, Wei, Changgeng, Cui, Chong-Chao, Cao, Bu-La, Guo, Yanhui, Wang, Lai-Sheng, Gu, Qinfen, Chen, Xuenian
• Format: Journal Article
• Language: English
• Published: Germany 25.02.2019
• Subjects: nucleophilicity; X-ray diffraction; reaction mechanisms; boron; alkali metals
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201812795

A facile synthesis of heavy alkali metal octahydrotriborates (MB H ; M=K, Rb, and Cs) has been developed. It is simply based on reactions of the pure alkali metals with THF⋅BH , does not require the use of electron carriers or the addition of other reaction media such as mercury, silica gel, or inert salts as for previous procedures, and delivers the desired products at room temperature in very high yields. However, no reactions were observed when pure Li or Na was used. The reaction mechanisms for the heavy alkali metals were investigated both experimentally and computationally. The low sublimation energies of K, Rb, and Cs were found to be key for initiation of the reactions. The syntheses can be carried out at room temperature because all of the elementary reaction steps have low energy barriers, whereas reactions of LiBH /NaBH with THF⋅BH have to be carried out under reflux. The high stability and solubility of KB H were examined, and a crystal structure thereof was obtained for the first time.