Detection of Cyclo-N 5 - in THF Solution.

Compelling evidence has been found for the formation and direct detection of the cyclopentazole anion (cyclo-N-5(-)) in solution. The anion was prepared from phenyl-pentazole in two steps: reduction by an alkali metal to form the phenylpentazole radical anion, followed by thermal dissociation to yield cyclo-N-5(-). The reaction solution was analyzed by HPLC coupled with negative mode mass spectrometry. A signal with m/z 70 was eluted about 2.1 min after injection of the sample. Its identification as N-5 was supported by single and double labeling with N-15, which yielded signals at m/z = 71 and 72, respectively, with identical retention times in the HPLC column. MS/MS analysis of the m/z = 70 signal revealed a dissociation product with m/z = 42, which can be assigned to N-3(-). To our knowledge this is the first preparation of cyclo-N-5(-) in the bulk. The compound is indefinitely stable at temperatures below -40 degrees C, and has a half-life of a few minutes at room temperature.