An Improved Method for the Synthesis of M₂[B₁₂H₁₂] (M = Na, K) and Their Formation Mechanism

Polyhedral boranes have potential applications in medicine and material science due to their unique structure and stability. However, tedious and low-yield synthetic methods limited their application. Herein, we have developed a facile large-scale synthetic method for M₂[B₁₂H₁₂] (M = Na, K) by the reaction of MBH₄ with N,N-dipropylaniline borane in diglyme at 120 or 140 °C in up to 88% yield. The mechanistic studies indicated that intermediates, such as [B₃H₈]^- and [B₉H₁₄]^-, were formed in the formation process of [B₁₂H₁₂]^2- anion, similar to previously reported. The formation of B₂H₆ from the N,N-dipropylaniline borane adducts is most important. The developed method avoided using toxic materials, with high yield, easily scaled up, raw materials are readily available. Additionally, the starting material, N,N-dipropylaniline, could be repeatedly used at least three times with similar yields, which is an economical way to facilitate industrial synthesis. It is believed that this method will support further application of Na₂[B₁₂H₁₂] and K₂[B₁₂H₁₂] as solid electrolytes for an all-solid-state batteries.