Synthesis and Characterization of Nitro-, Trinitromethyl-, and Fluorodinitromethyl-Substituted Triazolyl- and Tetrazolyl-trihydridoborate Anions.

The problem of preparing energetic, exclusively mono-azolyl substituted hydridoborate anions in high yield and purity from [BH4 ]- and nitroazoles by hydrogen elimination was overcome by reacting the corresponding nitroazolate anions with the BH3 adducts BH3 ⋅S(CH3 )2 or BH3 ⋅THF. The highly-energetic, nitro-, trinitromethyl-, and fluorodinitromethyl- substituted triazolyl- and tetrazolyl-trihydridoborate anions were synthesized in this manner and characterized by vibrational and multinuclear NMR spectroscopy and their crystal structures. The use of excess BH3 resulted in some cases in the addition of a second BH3 molecule bound more-weakly to one of the nitrogen atoms of the azole ring. All monoazolyl-trihydridoborates were thermally less stable than the parent azolate anions. A decomposition product of tetraphenylphosphonium (5-(trinitromethyl)-5H-2λ4 -tetrazol-2-yl)trihydridoborate, the tetraphenyl-phosphonium (dinitro-1H-tetrazol-5-yl)methanide monohydrate, was also structurally characterized, providing some insight into the decomposition pathways of the nitromethyl-substituted azolyltrihydridoborate anions.