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

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• 作者：Hongmin Li ; Dingqing Li ; Xiaoqing Zeng ; Kun Liu ; Helmut Beckers ; Henry F. Schaefer ; III ; Brian J. Esselman ; Robert J. McMahon
• 刊名：Journal of Physical Chemistry A
• 出版年：2015
• 出版时间：August 20, 2015
• 年：2015
• 卷：119
• 期：33
• 页码：8903-8911
• 全文大小：494K
• ISSN：1520-5215

文摘

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鈥揘CO (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鈥搒yn structure (I) readily converts into the syn鈥揳nti conformer (螖H_exptl = 1.1 卤 0.5 kcal mol^鈥?), which undergoes decomposition in two competing pathways: a concerted path to N₃鈥揘CO (III) or a stepwise route to (III) via the nitrene intermediate N₃C(O)N ¹(II). The calculated activation barriers (E_a) are almost the same (鈭?3 kcal mol^鈥?, B3LYP/6-311+G(3df)). Further decomposition of (III) occurs through a concerted fragmentation into 2 N₂ + CO with a moderate E_a of 22 kcal mol^鈥?, and this process is compared to the isoelectronic species N₃鈥揘₃ 鈫?3 N₂ (E_a = 17 kcal mol^鈥?) and OCN鈥揘CO 鈫?N₂ + 2 CO (61 kcal mol^鈥?). 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 (E_a = 30 kcal mol^鈥?) 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鈥揅鈥揘 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).