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A safe and efficient synthetic method for MB3H8 (M = Na, K, Rb and Cs) has been developed with excellent yields by directly reacting the corresponding MBH4 with the dimethyl sulfide borane complex (DMS·BH3). A general mechanism for constructing B3H8−, a basic unit for building polyhedral boranes, has been unravelled. [ABSTRACT FROM AUTHOR]

A facile synthesis of heavy alkali metal octahydrotriborates (MB3H8; M=K, Rb, and Cs) has been developed. It is simply based on reactions of the pure alkali metals with THF⋅BH3, 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 LiBH4/NaBH4 with THF⋅BH3 have to be carried out under reflux. The high stability and solubility of KB3H8 were examined, and a crystal structure thereof was obtained for the first time. Sublime reactivity: Unsolvated MB3H8 (M=K, Rb, and Cs) salts were prepared by reactions of the respective pure alkali metals with THF⋅BH3 in high yield at room temperature, and the structure of unsolvated KB3H8 was elucidated. The proposed reaction mechanisms are based on experimental and theoretical results. It was found that the physical properties of the alkali metals play a crucial role. [ABSTRACT FROM AUTHOR]

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A facile synthesis of heavy alkali metal octahydrotriborates (MB3H8; M=K, Rb, and Cs) has been developed. It is simply based on reactions of the pure alkali metals with THF⋅BH3, 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 LiBH4/NaBH4 with THF⋅BH3 have to be carried out under reflux. The high stability and solubility of KB3H8 were examined, and a crystal structure thereof was obtained for the first time. Sublime reactivity: Unsolvated MB3H8 (M=K, Rb, and Cs) salts were prepared by reactions of the respective pure alkali metals with THF⋅BH3 in high yield at room temperature, and the structure of unsolvated KB3H8 was elucidated. The proposed reaction mechanisms are based on experimental and theoretical results. It was found that the physical properties of the alkali metals play a crucial role. [ABSTRACT FROM AUTHOR]

A facile synthesis of heavy alkali metal octahydrotriborates (MB3H8; M=K, Rb, and Cs) has been developed. It is simply based on reactions of the pure alkali metals with THF⋅BH3, 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 LiBH4/NaBH4 with THF⋅BH3 have to be carried out under reflux. The high stability and solubility of KB3H8 were examined, and a crystal structure thereof was obtained for the first time. [ABSTRACT FROM AUTHOR]