Unraveling the Mechanism of cyclo-N₅^– Production through Selective C–N Bond Cleavage of Arylpentazole with Ferrous Bisglycinate and m-Chloroperbenzonic Acid: A Theoretical Perspective

Abstract

Very recently, the bulk synthesis of cyclo-N 5 − from arylpentazole through the treatment with m-chloroperbenzonic acid (m-CPBA) and ferrous bisglycinate ([Fe(Gly) 2 ]) (Zhang, C., et al. Science 2017, 355, 374) has greatly promoted the application of pentazolate anion as a novel high-performance energetic material. Yet the mechanism for this reaction is still unexplored. Herein we perform mechanistic studies on the selective C−N bond cleavage in arylpentazole by using density functional theory methods. The direct C−N bond activation by m-CPBA was computed to be kinetically inaccessible. Instead, the oxidation of [Fe(Gly) 2 ] by m-CPBA is much favorable, which leads to the generation of a high-valent iron(IV)−oxo product. The Fe(IV)− oxo intermediate has been examined by UV−vis absorption spectra experiments and further verified by excited-state calculations. It is found that the Fe(IV)−oxo serves as the key intermediate for the C−N bond activation of arylpentazole and the cyclo-N 5 − generation. Our calculations clarified the key mechanistic details of the cyclo-N 5 − generation, and the factors that affect the production yield are further discussed.

Recent advances in studying the nonnegligible role of noncovalent interactions in various types of energetic molecular crystals

“…In addition, the π-π interactions emerging between energetic molecules also have a significant impact on the initiation and decomposition mechanisms of the energetic crystals, which may guide the optimization of design and synthesis routes for outstanding energetic materials. Shang et al 83 precursor have shown that the π-π stacking mode between the aromatic moieties of benzyl groups is mainly responsible for the reduction of the energy barrier of the ratedetermining step that facilitates the subsequent reaction to form the five-membered ring. 84 Similarly, the mechanistic investigations of the initial decomposition mechanism of FOX-7 and RDX reported by Ma et al have revealed that the interlayer π-π interactions in the crystalline state will significantly increase the reaction barrier of the primary decomposition pathways compared to that in the gas phase.…”

“…In addition, the π–π interactions emerging between energetic molecules also have a significant impact on the initiation and decomposition mechanisms of the energetic crystals, which may guide the optimization of design and synthesis routes for outstanding energetic materials. Shang et al 83 reported a detailed description of the reaction mechanisms in the production process of cyclo-N 5 − under the treatment of ferrous bisglycinate using the quantum chemistry method. The results revealed that the high-valent Fe( iv )-oxo intermediate was produced through a favorable route involving the oxidation of ferrous bisglycinate, which can serve as a key structure during the C–N bond activation and N 5 − anion generation.…”

Theoretical study on N‐oxide pentazolate high‐energy‐density materials: Toward excellent energetic performance and good stability

“…[ 4,5 ] Because of the huge energy difference among N–N (159.9 kJ mol −1 ), N═N (418.2 kJ mol −1 ), and NN (946 kJ mol −1 ) bonds, poly‐nitrogen materials are able to release a lot of energy by breaking the N–N, N═N bonds and the formation of N 2 . [ 6 ]…”

“…[4,5] Because of the huge energy difference among N-N (159.9 kJ mol À1 ), N═N (418.2 kJ mol À1 ), and N N (946 kJ mol À1 ) bonds, poly-nitrogen materials are able to release a lot of energy by breaking the N-N, N═N bonds and the formation of N 2 . [6] Since the first found of N 2 in 1772, poly-nitrogen compounds have gone through a long and difficult development. Until now, only azide ion (N 3 À ), N 5 + cation, cyclo-N 5 À anion, and polymeric nitrogen (cg-N) under high pressure have been synthesized.…”

Characterization of thermal decomposition mechanism and combustion performance of 4,4’‐azobis(1,2,4‐triazole)**

“…Traditional CHON type energetic materials use nitro groups as the main functional group, and the main energy source is the oxidation-reduction reaction between oxygen and carbon carried by nitro groups [1][2]. The demand for novel high energy density materials has been growing in modern society [3][4][5]. New compounds that achieve higher energy density and nitrogen content levels are the material basis for improving the performance of energetic materials [6][7].…”