High Yield Autoclave Synthesis of pure M2B12H12 (M = Na, K)

Metal dodecaborates (M x B 12 H 12 ) 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 B 12 H 12 2– derivatives. In this work, we report a simple, efficient, and environmentally benign solvothermal method to prepare diffraction and 11 B NMR pure Na 2 B 12 H 12 (85% yield) and K 2 B 12 H 12 (84% yield). This new synthetic approach is based on the use of the borane dimethyl sulfide complex (DMS·BH 3 ) and borohydrides (NaBH 4, KBH 4 ) heated at different temperatures in diglyme in an autoclave. It was found that high-purity Na 2 B 12 H 12 ·diglyme solvate is obtained via an intermediate formation of B 3 H 8 –, B 9 H 14 –, and B 11 H 14 –, which are all soluble in diglyme. Heating under vacuum is shown to be efficient for removing the coordinated diglyme, allowing the formation of unsolvated Na 2 B 12 H 12 . Autoclave synthesis starting from KBH 4 directly yields solvent-free K 2 B 12 H 12, and ball-milling KBH 4 prior to the synthesis enabling us to significantly improve the final yield. The new synthetic method paves the way for large-scale synthesis of M x B 12 H 12 derivatives, enabling to envisage a wider scope of practical applications.