Detection of Cyclo‐N₅⁻ in THF Solution

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 15N, 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.

Pentazole and Ammonium Pentazolate: Crystalline Hydro-Nitrogens at High Pressure

“…Pentazole N 5 H, a hydro-nitrogen molecule containing all-nitrogen aromatic ring N 5 , has been in the focus of intensive experimental efforts of synthetic chemists for at least a century [1][2][3][4] Although theory predicted its existence as a metastable species with a local minimum on the potential energy surface confined by a large activation barrier 5 , this planar pentagon of N atoms connected to one H atom is short-lived in the gas phase, making the synthesis of this last member of azole series very difficult [6][7][8] . After many unsuccessful attempts, the isolated but short-lived N − 5 anion has been produced in the gas phase 9,10 , followed by its recent observation in a THF solution 11 . However, synthesis of hydrogen-containing N 5 H still remains a challenge.…”

Pentazole (N5H) as a possible catalyst for CO2 activation: Density functional theory (DFT) and ab initio molecular dynamics (AIMD) studies

“…[ 42 ] The prime report published by Haas et al in 2016 has ended the race for detection of N 5 − in solution. [ 43 ] In their research, they showed the formation, separation and stability for N 5 – ion. The synthesis of pentazolate anion is carried out by the reduction of phenylpentazole using an alkali metal, which is followed by thermal dissociation.…”

“…The synthesis of pentazolate anion is carried out by the reduction of phenylpentazole using an alkali metal, which is followed by thermal dissociation. [ 43 ] Countless experiments and efforts were made to figure out the structure, stability and properties of numerously diversified N‐ring structured compounds. [ 44–51 ] An attempt has also been made to probe the stability of N 5 H in water clusters.…”

Density functional theory studies on two novel poly‐nitrogen compounds: N5+N3− and N5+N5−

“…With the progress of synthetic technology, more and more poly‐nitrogen species have been discovered and synthesized. [ 11–14 ] The most representative of them are three relatively stable ionic poly‐nitrogen species, N 3 − , N 5 + , and recently synthesized N 5 − . They can all exist in the form of salts that are stable at normal temperature and pressure.…”