A safe and efficient synthetic method for alkali metal octahydrotriborates, unravelling a general mechanism for constructing the delta B3 unit of polyhedral boranes.

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.