Detection of Cyclo-N5- in THF Solution

Boris Bazanov; Uzi Geiger; Raanan Carmieli; Dan Grinstein; Shmuel Welner; Yehuda Haas

doi:10.1002/anie.201605400

Detection of Cyclo-N₅^- in THF Solution

Angew Chem Int Ed Engl. 2016 Oct 10;55(42):13233-13235. doi: 10.1002/anie.201605400.

Authors

Boris Bazanov¹, Uzi Geiger¹, Raanan Carmieli², Dan Grinstein¹, Shmuel Welner¹, Yehuda Haas³

Affiliations

¹ Institute of Chemistry, Safra Campus, The Hebrew University of Jerusalem, 91904, Jerusalem, Israel.
² Head of the EPR lab, Department of Chemical Research Support, Weizmann Institute of Science, 76100, Rehovot, Israel.
³ Institute of Chemistry, Safra Campus, The Hebrew University of Jerusalem, 91904, Jerusalem, Israel. yehuda.haas@mail.huji.ac.il.

PMID: 27385080
DOI: 10.1002/anie.201605400

Abstract

Compelling evidence has been found for the formation and direct detection of the cyclopentazole anion (cyclo-N₅^- ) 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-N₅^- . 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 N₅ 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 N₃^- . To our knowledge this is the first preparation of cyclo-N₅^- 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.

Keywords: cyclopentazolate anion; high energy density materials; nitrogen heterocycles; phenylpentazole; radical anions.