High Yield Autoclave Synthesis of pure MBH (M = Na, K).

Metal dodecaborates (MBH) are a versatile class of materials used in polymer chemistry and cancer treatment and are promising candidates as electrolytes for solid-state batteries. However, a general and scalable approach has not yet been developed for producing high-purity BH derivatives. In this work, we report a simple, efficient, and environmentally benign solvothermal method to prepare diffraction and B NMR pure NaBH (85% yield) and KBH (84% yield). This new synthetic approach is based on the use of the borane dimethyl sulfide complex (DMS·BH) and borohydrides (NaBH, KBH) heated at different temperatures in diglyme in an autoclave. It was found that high-purity NaBH·diglyme solvate is obtained via an intermediate formation of BH, BH, and BH, which are all soluble in diglyme. Heating under vacuum is shown to be efficient for removing the coordinated diglyme, allowing the formation of unsolvated NaBH. Autoclave synthesis starting from KBH directly yields solvent-free KBH, and ball-milling KBH prior to the synthesis enabling us to significantly improve the final yield. The new synthetic method paves the way for large-scale synthesis of MBH derivatives, enabling to envisage a wider scope of practical applications.