Unraveling the Mechanism of <i>cyclo</i>-N<sub>5</sub><sup>–</sup> Production through Selective C–N Bond Cleavage of Arylpentazole with Ferrous Bisglycinate and <i>m</i>-Chloroperbenzonic Acid: A Theoretical Perspective
Fangjian Shang, Runze Liu, Jianyong Liu, Panwang Zhou, Chaoyang Zhang, Shuhui Yin, Keli Han
Abstract
Very recently, the bulk synthesis of cyclo-N5– 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-N5– generation. Our calculations clarified the key mechanistic details of the cyclo-N5– generation, and the factors that affect the production yield are further discussed.