Decomposition of Sulfonyl Azide Isocyanate and Sulfonyl Diazide: The Oxygen-Shifted Curtius Rearrangement via Sulfonyl Nitrenes.

Sulfonyl azide isocyanate, (OCN)S(O)N, was prepared and characterized by IR (gas, matrix-isolation), Raman (liquid), and UV-vis spectroscopy. Upon flash vacuum pyrolysis (FVP) at ca. 1000 K, gaseous (OCN)S(O)N decomposes completely and yields fragments N, SO, SO, NCN, N, NCO, CO, CN, and NO. In contrast, the azide splits off N and furnishes a transient triplet sulfonyl nitrene intermediate (OCN)S(O)N upon a 266 nm laser irradiation in solid Ne-matrix at 2.8 K. Subsequent photolysis of the nitrene with visible light (λ = 380-450 nm) results in oxygen-shifted Curtius rearrangement to a novel nitroso sulfoxide (OCN)S(O)NO. For comparison, the photodecomposition of the closely related sulfonyl diazide OS(N) in a solid Ar matrix was also studied. Upon an ArF excimer laser (193 nm) photolysis, OS(N) decomposes and yields N, SO, and OSNNO via the intermediacy of an elusive sufonyl nitrene NS(O)N. Further visible light irradiation (λ > 395 nm) leads to depletion of NS(O)N and OSNNO and concomitant formation of SO and N. The identification of the intermediates in cryogenic matrixes by IR spectroscopy was supported by N-labeling experiments and quantum chemical calculations. The mechanism for the decomposition of both sulfonyl azides (OCN)S(O)N and OS(N) was discussed on the basis of the observed intermediates and the calculated potential energy profiles.