Toward Understanding the Decomposition of Carbonyl Diazide (N₃)₂C═O and Formation of Diazirinone cycl-N₂CO: Experiment and Computations

Abstract

Carbonyl diazide, (N3)2CO (I), is a highly explosive compound. The isolation of the substance in a neat form was found to provide unique access to two other high-energy molecules, namely, N3-NCO (III) and cycl-N2CO (IV), among the decomposition products of (I). To understand the underlying reaction mechanism, the decomposition reactions including the thermal conversion of two conformers of (I) were revisited, and the potential energy surface (PES) was computationally explored by using the methods of B3LYP/6-311+G(3df) and CBS-QB3. The most stable syn-syn structure (I) readily converts into the syn-anti conformer (ΔHexptl = 1.1 ± 0.5 kcal mol(-1)), which undergoes decomposition in two competing pathways: a concerted path to N3-NCO (III) or a stepwise route to (III) via the nitrene intermediate N3C(O)N (1)(II). The calculated activation barriers (Ea) are almost the same (∼33 kcal mol(-1), B3LYP/6-311+G(3df)). Further decomposition of (III) occurs through a concerted fragmentation into 2 N2 + CO with a moderate Ea of 22 kcal mol(-1), and this process is compared to the isoelectronic species N3-N3 → 3 N2 (Ea = 17 kcal mol(-1)) and OCN-NCO → N2 + 2 CO (61 kcal mol(-1)). No low-energy pathway leading to (IV) was found on the singlet PES. However, the intervention of triplet ground-state (3)(II) from the initially generated (1)(II) through an intersystem crossing (ISC) offers a likely approach to (IV); that is, (3)(II) can decompose in a concerted process (Ea = 30 kcal mol(-1)) by eliminating one N2 to yield the disfavored OCNN (3)(VI). A careful intrinsic reaction coordinate analysis and a combined energy scan of the N-C-N angle reveals a bifurcation point on this triplet PES, which allows a spin crossover to the singlet PES along the reaction coordinate and eventually leads to the formation of the metastable diazirinone (IV).

Synthesis and Chemistry of Organic Geminal Di- and Triazides

“…Furthermore the structure was confirmed by X-ray diffraction. Of note, all experimental data were in good agreement with several independent calculations [15,16,17,18,19]. Very interesting from a preparative point of view, carbonyl diazide ( 2 ) is thermally stable with a defined melting point of 16 °C, and it shows a high impact sensitivity.…”

“…Very interesting from a preparative point of view, carbonyl diazide ( 2 ) is thermally stable with a defined melting point of 16 °C, and it shows a high impact sensitivity. Regarding the reactivity of carbonyl diazide ( 2 ), the photolysis [20] and the thermal decomposition [19,21,22] were investigated by means of infrared spectroscopy and theoretical calculations (Scheme 3). The irradiation of matrix-isolated carbonyl diazide ( 2 ) with UV-light (255 nm) causes the loss of molecular nitrogen and the formation of azido carbonyl nitrene 12 , which rearranges under visible light (455 nm) to give azido isocyanate ( 13 ).…”

Cleavage of the N≡N Triple Bond and Unpredicted Formation of the Cyclic 1,3‐Diaza‐2,4‐Diborete (FB)2N2 from N2 and Fluoroborylene BF

“…We recall that C is observed only in freshly deposited samples, and it disappeared already upon annealing to 15 K. Cyclic C is isolectronic to the known diazirinone, OC( η 2 ‐N 2 ), [23a] and although C should be more stable because of a higher barrier and a lower dissociation energy, [23b] the N=N bond in C is strongly activated and it reacts readily with a second singlet FB molecule to yield A through a very low energy barrier of 0.5 kcal mol −1 (Figure S5).…”

Contrasting Photolytic and Thermal Decomposition of Phenyl Azidoformate: The Curtius Rearrangement Versus Intramolecular C–H Amination

“…The missing nitrene intermediate (PhO–C­(O)­N) in the decomposition of PhO–C­(O)­N 3 and the absence of the evidence for its Curtius rearrangement to PhONCO in the previous studies requires a reinvestigation of the underlying mechanism from both aspects of experiment and theory. Continuing our interest in the decomposition of α-oxoazides (RC­(O)­N 3 , − RS­(O)­N 3 , , R 2 P­(O)­N 3 , and RS­(O) 2 N 3 − ), herein we report a comprehensive study of the decomposition of PhO–C­(O)­N 3 by combining laser photolysis, flash vacuum pyrolysis, matrix-isolation IR and EPR spectroscopies, and quantum chemical calculations.…”