Curtius-Type Rearrangement of Sulfinyl Azides: A Matrix Isolation and Computational Study.

The highly unstable methyl sulfinyl azide, CHS(O)N, has been synthesized and characterized for the first time. In the gas phase, CHS(O)N decomposes quickly at room temperature (300 K) with an estimated half-life () of 7 min. Upon irradiation at 266 nm in cryogenic Ar (10 K) and Ne (3 K) matrices, the azide extrudes molecular nitrogen by yielding the novel sulfinyl nitrene intermediate CHS(O)N in the closed-shell singlet ground state, which has been characterized with matrix-isolation IR and UV-vis spectroscopy. Prolonged irradiation at 266 nm causes Curtius rearrangement of the nitrene to form -sulfinylamine CHNSO and -nitrosothiol CHSNO. By high-vacuum flash pyrolysis (HVFP) at 800 K, CHS(O)N also decomposes and furnishes CHS(O)N with minor fragmentation products HNSO and CH in the gas phase. A similar photo-induced Curtius-type rearrangement of trifluoromethyl sulfinyl azide CFS(O)N to CFNSO and CFSNO has also been observed in matrices. According to the theoretical calculations at the CCSD(T)/aug-cc-pVTZ//B3LYP/6-311++G (3df,3pd) level of theory, the rearrangement of CHS(O)N prefers a stepwise pathway by initial formation of the nitrene intermediate CHS(O)N. In line with the thermal persistence of CHS(O)N in the gas phase, the barriers for its subsequent rearrangement are higher than 30 kcal mol.