Wan Huabin, Xu Jian, Liu Qian, Li Hongmin, Lu Yan, Abe Manabu, Zeng Xiaoqing
College of Chemistry, Chemical Engineering and Materials Science, Soochow University , 215123 Suzhou, P. R. China.
Department of Chemistry, Graduate School of Science, Hiroshima University , 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
J Phys Chem A. 2017 Nov 16;121(45):8604-8613. doi: 10.1021/acs.jpca.7b07969. Epub 2017 Nov 2.
The decomposition of phenyl azidoformate, PhOC(O)N, was studied by combining matrix isolation spectroscopy and quantum chemical calculations. Upon UV laser photolysis (193 and 266 nm), the azide isolated in cryogenic noble gas matrices (Ne and Ar, 2.8 K) decomposes into N and a novel oxycarbonylnitrene PhOC(O)N, which was identified by matrix-isolation IR spectroscopy (with N labeling) and EPR spectroscopy (|D/hc| = 1.620 cm and |E/hc| = 0.024 cm). Subsequent visible-light irradiation (532 nm) causes rearrangement of the nitrene into phenoxy isocyanate PhONCO with complex secondary fragmentation (PhO· + ·NCO) and radical recombination species in matrices. The observation of PhONCO provides solid evidence for the Curtius rearrangement of phenyl azidoformate. In sharp contrast, flash vacuum pyrolysis (FVP) of PhOC(O)N at 550 K yields N and exclusively the intramolecular C-H amination product 3H-benzooxazol-2-one. FVP at higher temperature (700 K) leads to further dissociation into CO, HNCO, and ring-contraction products. To account for the very different photolytic and thermal decomposition products, the underlying mechanisms for the Curtius rearrangement (concerted and stepwise) of PhOC(O)N and the intramolecular C-H amination of the nitrene in both singlet and triplet states are discussed with the aid of quantum chemical calculations using the B3LYP, CBS-QB3, and CASPT2 methods.
通过结合基质隔离光谱法和量子化学计算，研究了苯基叠氮甲酸酯（PhOC(O)N）的分解。在紫外激光光解（193和266 nm）时，低温稀有气体基质（Ne和Ar，2.8 K）中隔离的叠氮化物分解为N和一种新型的氧羰基氮烯PhOC(O)N，通过基质隔离红外光谱（用N标记）和电子顺磁共振光谱（|D/hc| = 1.620 cm和|E/hc| = 0.024 cm）对其进行了鉴定。随后的可见光照射（532 nm）会使氮烯重排为苯氧基异氰酸酯PhONCO，同时在基质中伴有复杂的二次碎片化（PhO· + ·NCO）和自由基重组产物。PhONCO的观测为苯基叠氮甲酸酯的库尔提斯重排提供了确凿证据。与之形成鲜明对比的是，PhOC(O)N在550 K下的快速真空热解（FVP）产生N，且仅生成分子内C-H胺化产物3H-苯并恶唑-2-酮。在更高温度（700 K）下的FVP会导致进一步分解为CO、HNCO和环收缩产物。为了解释截然不同的光解和热分解产物，借助使用B3LYP、CBS-QB3和CASPT2方法的量子化学计算，讨论了PhOC(O)N的库尔提斯重排（协同和分步）以及单线态和三线态氮烯分子内C-H胺化的潜在机制。
