Preparation of the Cyclopentazole Anion in the Bulk: A Computational Study

Abstract

The cyclopentazole anion (cyclo-N5(-)), calculated to be a stable species, was prepared in the gas phase but attempts to synthesize it in the bulk have so far been futile. An aryl pentazole radical anion was suggested as a promising precursor in the gas phase. It is shown computationally that the radical anion (which may be prepared by reduction of the phenyl pentazole neutral) may indeed be used to form the cyclopetazolate anion in the gas phase and in liquid solution, alongside and in competition with the extrusion of N2 to produce the corresponding azide. In the gas phase, the C-N dissociation yields are very low due to much more efficient detachment of an electron. In polar solvents, ionization is suppressed and the primary yields of the two competing reactions are similar. The reaction must be carried out at low temperatures and special measures have to be taken to avoid recombination of the nascent cyclo-N5(-) with the geminate phenyl radical. A possible remedy is to use a solvent that reacts efficiently with the phenyl radical by H atom transfer.

Roads to pentazolate anion: a theoretical insight

“…23.1 kcal mol −1 for the pentazolate anion formation and 23.2 kcal mol −1 for the dinitrogen evolution. The same trend was reported using the average of three high accuracy methods [ 11 ]. As shown in electronic supplementary material, table S2, the solvent effect of THF has little impact on the correlative barriers.…”

“…Bazanov et al [ 10 ] in 2016 treated phenylpentazole (PPZ) with sodium in tetrahydrofuran (THF), and the mass spectrometry of PZA was detected with an elution time of 2.1 min after injection into the HPLC column. The electron transfer from sodium to PPZ also follows the radical anion mechanism [ 11 ]. The cleavage of the C–N bond competes with the evolution of dinitrogen.…”

“…Vij et al [7] in 2002 observed the m/z 70 (71 for a pentazole ring containing one 15 N) peak of mass spectrometry using electrospray ionization (ESI) at high collision voltages for p-pentazolylphenolate anion (p-PZPolA). The removal of aryl group of p-PZPolA undergoes an intersystem crossing between singlet and triplet states with a barrier of 63.8 kcal mol −1 at the CASSCF (12,11)/DZV level [8]. Östmark et al [9] in 2003 also discovered the peak of mass spectrometry using a relatively mild ionization, i.e.…”

A Joint Experimental and Computational Study of the Negative Ion Photoelectron Spectroscopy of the 1-Phospha-2,3,4-triazolate Anion, HCPN3–

“…7−9 Although the cyclo-pentazolate anion (N 5 − ) was observed in the gas phase more than a decade ago 10 and has been calculated to be a stable species, 11 attempts to synthesize it in large quantities have, at least thus far, been futile. 12 Consequently, the recent synthesis of P 2 N 3 − represents important progress in the study of all-pnictogen analogues of C 5 H 5 . 13−17 Formal replacement of both phosphorus atoms in P 2 N 3 − by CH groups yields the 1,2,3-triazolide anion, (CH) 2 N 3 − ( Figure 1).…”

Reactivity Indexes and Structure of Fullerenes

“…However, over time, new polynitrogenated species such as N 3 , N 4 , N 5 − and N 5 + have been discovered or posited, whose synthesis has either represented a challenge or turned out to be surprisingly simple [27][28][29][30]. In spite of this, until now, the species with the highest content of nitrogen produced in measurable quantities has contained 5 nitrogen atoms, meaning that in particular the cyclopentazole anion could be considered as a motivator for theoretical studies on its formation, as well as representing a building block towards more complex structures [31][32][33][34][35]. As species with higher nitrogen content have proved to be very unstable with respect to decomposition to N 2 , theoretical studies have outnumbered experimental ones.…”