An Improved Method to Synthesize M2[B12H12] (M = Li, Na) by the Sequential Addition of Different Solvents

The derivatives of [B₁₂H₁₂]²⁻ anion are an important part of polyhedral boranes and play a significant role in the fields of energy, materials, and biomedicine. The researchers have made a great effort to explore the efficient method to synthesize the [B₁₂H₁₂]²⁻ salts. However, the reported synthetic strategies are limited by the requirement of using toxic starting materials, harsh reaction conditions, and tedious and difficult work-up processes. Herein, we developed an efficient method to synthesize [B₁₂H₁₂]²⁻ salts with MBH₄ (M = Li, Na) and N,N-dibutylbenzenamine borane as the starting materials and by adding two kinds of solvents (DME and 1,4-dioxane or THF and 1,4-dioxane) into the system in a sequential order. M₂[B₁₂H₁₂] (M = Li, Na) was synthesized in 75%–86% yields, respectively. This method avoids high boiling point ether solvents and flammable, toxic starting materials. Moreover, the developed method is simple and efficient, as the products can precipitate from the reaction system, greatly simplifying the separation process.