Synthesis of NH₃·B₉H₁₃ and Its N-Alkyl Analogues: Toward the Polyhedral Azaboranes, M[NH₂B₉H₁₁] (M = Na, K)

Improved and effective methods for the synthesis of NH₃·B₉H₁₃ and its N-alkyl analogues have been developed with synthetically satisfying yield under mild conditions. The single-crystal structure of NH₃·B₉H₁₃ was determined for the first time, although it was found decades ago. These complexes possess high stability, suggesting promising potential applications in various reactions. Consequently, starting from the as-synthesized NH₃·B₉H₁₃, the new polyhedral azaboranes, M[NH₂B₉H₁₁] (M = Na, K), are successfully prepared by reacting with the corresponding MH with high yields. In the arachno-[NH₂B₉H₁₁]^- anion, the N atom is bonded to two B atoms and occupies a "framework" position. This conclusion is supported by the single-crystal structure analysis of the [18-crown-6·K·2THF][NH₂B₉H₁₁] adduct, which clearly distinguishes it from its parent compound NH₃·B₉H₁₃. In the latter, the N atom of NH₃ only coordinates with one B atom and does not significantly contribute to the arachno-structure. This work provides methods for preparing B₉H₁₃-based polyhedral azaboranes.