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

The highly unstable methyl sulfinyl azide, CH 3 S(O)N 3 , has been synthesized and characterized for the first time. In the gas phase, CH 3 S(O)N 3 decomposes quickly at room temperature (300 K) with an estimated half-life ( t 1/2 ) 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 CH 3 S(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 N -sulfinylamine CH 3 NSO and S -nitrosothiol CH 3 SNO. By high-vacuum flash pyrolysis (HVFP) at 800 K, CH 3 S(O)N 3 also decomposes and furnishes CH 3 S(O)N with minor fragmentation products HNSO and CH 2 in the gas phase. A similar photo-induced Curtius-type rearrangement of trifluoromethyl sulfinyl azide CF 3 S(O)N 3 to CF 3 NSO and CF 3 SNO 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 CH 3 S(O)N 3 prefers a stepwise pathway by initial formation of the nitrene intermediate CH 3 S(O)N. In line with the thermal persistence of CH 3 S(O)N in the gas phase, the barriers for its subsequent rearrangement are higher than 30 kcal mol -1 .