Photochemistry of Matrix Isolated (Trifluoromethyl)sulfonyl Azide, CF 3 SO 2 N 3 Xiaoqing Zeng,* ,† Helmut Beckers,* ,‡ Helge Willner, ‡ Patrik Neuhaus, § Dirk Grote, § and Wolfram Sander § † College of Chemistry, Chemical Engineering and Materials Science, Soochow University, 215123 Suzhou, China ‡ FB C-Anorganische Chemie, Bergische Universitä t Wuppertal, Gaussstrasse 20, 42119 Wuppertal, Germany § Lehrstuhl fü r Organische Chemie II, Ruhr-Universitä t Bochum, Universitä tsstraß 150, 44780 Bochum, Germany *S Supporting Information ABSTRACT: The photochemistry of matrix isolated (trifluoromethylsulfon- yl) azide, CF 3 SO 2 N 3 , has been studied at low temperatures. Upon ArF laser irradiation (λ = 193 nm), the azide eliminates N 2 and furnishes triplet [(trifluoromethyl)sulfonyl]nitrene, CF 3 SO 2 N, which has been characterized by IR and EPR spectroscopy. Upon subsequent UV light irradiation (λ = 260−400 nm) the nitrene converts to CF 3 NSO 2 and CF 3 S(O)NO through a Curtius-type rearrangement. Further two new species CF 2 NSO 2 F and FSNO were identified together with CF 2 NF, SO 2 ,F 2 CO, CF 3 NO, and SO as side products. In addition, triplet nitrene CF 3 N was detected by its EPR and IR spectra. The complex stepwise photodecomposition of matrix isolated CF 3 SO 2 N 3 is discussed in terms of the observed photolysis products and quantum chemical calculations. ■ INTRODUCTION Sulfonyl azides, RSO 2 N 3 , are important reagents in synthetic chemistry. 1−4 Similar to the reactions of related carbonyl azides, 5,6 both photodecomposition and thermal decomposition reactions of sulfonyl azides have been extensively studied in solution. The intervention of sulfonylnitrenes, RSO 2 N, were chemically inferred from secondary decomposition prod- ucts. 7−17 A number of triplet sulfonylnitrenes have already been experimentally detected among the photolysis products of the corresponding azides by electron paramagnetic resonance (EPR) spectroscopy at low temperatures. 18−20 These early studies strongly suggested that sulfonylnitrenes adopt triplet ground states, and no straightforward evidence for a Curtius- type rearrangement was obtained. Recently, laser flash photolysis of arylsulfonyl azide was studied by ultrafast absorption spectroscopy (IR and UV− vis). 21,22 The (2-naphthylsulfonyl)nitrene intermediate (2- NpSO 2 N) has been verified to be formed in both the singlet and the triplet states, whereas the rather short-lived (τ = 700 ± 300 ps in CCl 4 ) singlet nitrene was found to relax to the long- lived triplet ground state. Still no conclusive evidence have been established for a Curtius-type rearrangement of 2-NpSO 2 N. 21 The complex photochemistry in solution and the congested spectra of the photolysis products prevented as yet an unambiguous detection of the potential rearrangement product 2-NpNSO 2 . In comparison to the complex photochemistry in solution, photolysis of the facile sulfonyl azide FSO 2 N 3 in solid noble gas matrices was found to be much simpler. 23 Upon ArF excimer laser photolysis (193 nm), triplet nitrene FSO 2 N was obtained and characterized by IR, UV−vis, and EPR spectroscopy. In addition to the minor side products SO + FNO and FN + SO 2 , the oxygen-shifted Curtius-type rearrangement product FS(O)- NO was identified after subsequent irradiation with light of λ > 320 nm. A similar rearrangement has been verified for the related α-oxo nitrene F 2 P(O)N → F 2 PNO. 24 The first unambiguous spectroscopic proof for the expected Curtius- type rearrangement from RSO 2 N to a sulfuryl imide RNSO 2 was achieved for FSO 2 N (R = F). 25 Traces of FNSO 2 were identified among the photolysis (λ = 266 nm) products of FSO 2 N, 25 which was synthesized in a high-yield (∼70%) by flash pyrolysis of FSO 2 N 3 . In contrast, no Curtius-type rearrangement product was found among the pyrolysis products of FSO 2 N 3 , and also the previously studied flash pyrolysis of CF 3 SO 2 N 3 revealed very different results. No sulfonylnitrene CF 3 SO 2 N but O 2 SN and CF 3 were obtained as main decomposition products. 26 The rich and diverse chemistry of sulfonyl azides prompted us to study the photodecomposition of the broadly used diazo transfer reagent (trifluoromethyl)sulfonyl azide, CF 3 SO 2 N 3 , 27 in solid noble gas matrices by IR and EPR spectroscopy. The stepwise decomposition of the azide to form CF 3 NSO 2 and Special Issue: Markku Rasanen Festschrift Received: June 23, 2014 Revised: July 24, 2014 Article pubs.acs.org/JPCA © XXXX American Chemical Society A dx.doi.org/10.1021/jp506243s | J. Phys. Chem. A XXXX, XXX, XXX−XXX