Chloro- and Dichloro-methylsulfonyl Nitrenes: Spectroscopic Characterization, Photoisomerization, and Thermal Decomposition

Chloro- and dichloro-methylsulfonyl nitrenes, CH(2)ClS(O)(2)N and CHCl(2)S(O)(2)N, have been generated from UV laser photolysis (193 and 266 nm) of the corresponding sulfonyl azides CH(2)ClS(O)(2)N(3) and CHCl(2)S(O)(2)N(3), respectively. Both nitrenes have been characterized with matrix-isolation IR and EPR spectroscopy in solid N(2) (10 K) and glassy toluene (5 K) matrices. Triplet ground-state multiplicity of CH(2)ClS(O)(2)N (|D/hc| = 1.57 cm(−1) and |E/hc| = 0.0026 cm(−1)) and CHCl(2)S(O)(2)N (|D/hc| = 1.56 cm(−1) and |E/hc| = 0.0042 cm(−1)) has been confirmed. In addition, dichloromethylnitrene CHCl(2)N (|D/hc| = 1.57 cm(−1) and |E/hc| = 0 cm(−1)), formed from SO(2)-elimination in CHCl(2)S(O)(2)N, has also been identified for the first time. Upon UV light irradiation (365 nm), the two sulfonyl nitrenes R–S(O)(2)N (R = CH(2)Cl and CHCl(2)) undergo concomitant 1,2-R shift to N-sulfonlyamines R–NSO(2) and 1,2-oxygen shift to S-nitroso compounds R–S(O)NO, respectively. The identification of these new species with IR spectroscopy is supported by (15)N labeling experiments and quantum chemical calculations at the B3LYP/6-311++G(3df,3pd) level. In contrast, the thermally-generated sulfonyl nitrenes CH(2)ClS(O)(2)N (600 K) and CHCl(2)S(O)(2)N (700 K) dissociate completely in the gas phase, and in both cases, HCN, SO(2), HCl, HNSO, and CO form. Additionally, ClCN, OCCl(2), HNSO(2), •NSO(2), and the atmospherically relevant radical •CHCl(2) are also identified among the fragmentation products of CHCl(2)S(O)(2)N. The underlying mechanisms for the rearrangement and decomposition of CH(2)ClS(O)(2)N and CHCl(2)S(O)(2)N are discussed based on the experimentally-observed products and the calculated potential energy profile.