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

Abstract

Sulfonyl azide isocyanate, (OCN)S(O)2N3, 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)2N3 decomposes completely and yields fragments N2, SO2, SO3, NCN, N3, NCO, CO, CN, and NO. In contrast, the azide splits off N2 and furnishes a transient triplet sulfonyl nitrene intermediate (OCN)S(O)2N 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 O2S(N3)2 in a solid Ar matrix was also studied. Upon an ArF excimer laser (193 nm) photolysis, O2S(N3)2 decomposes and yields N2, SO2, and OSNNO via the intermediacy of an elusive sufonyl nitrene N3S(O)2N. Further visible light irradiation (λ > 395 nm) leads to depletion of N3S(O)2N and OSNNO and concomitant formation of SO2 and N2. The identification of the intermediates in cryogenic matrixes by IR spectroscopy was supported by 15N-labeling experiments and quantum chemical calculations. The mechanism for the decomposition of both sulfonyl azides (OCN)S(O)2N3 and O2S(N3)2 was discussed on the basis of the observed intermediates and the calculated potential energy profiles.