Detection of Cyclo‐N 5 − in THF Solution

Abstract 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 phenylpentazole 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 15 N, 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 °C, and has a half‐life of a few minutes at room temperature.