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Abstract
Chloro- and dichloro-methylsulfonyl nitrenes, CH2ClS(O)2N and CHCl2S(O)2N, have been generated from UV laser photolysis (193 and 266 nm) of the corresponding sulfonyl azides CH2ClS(O)2N3 and CHCl2S(O)2N3, respectively. Both nitrenes have been characterized with matrix-isolation IR and EPR spectroscopy in solid N2 (10 K) and glassy toluene (5 K) matrices. Triplet ground-state multiplicity of CH2ClS(O)2N (|D/hc| = 1.57 cm−1 and |E/hc| = 0.0026 cm−1) and CHCl2S(O)2N (|D/hc| = 1.56 cm−1 and |E/hc| = 0.0042 cm−1) has been confirmed. In addition, dichloromethylnitrene CHCl2N (|D/hc| = 1.57 cm−1 and |E/hc| = 0 cm−1), formed from SO2-elimination in CHCl2S(O)2N, has also been identified for the first time. Upon UV light irradiation (365 nm), the two sulfonyl nitrenes R–S(O)2N (R = CH2Cl and CHCl2) undergo concomitant 1,2-R shift to N-sulfonlyamines R–NSO2 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 15N labeling experiments and quantum chemical calculations at the B3LYP/6-311++G(3df,3pd) level. In contrast, the thermally-generated sulfonyl nitrenes CH2ClS(O)2N (600 K) and CHCl2S(O)2N (700 K) dissociate completely in the gas phase, and in both cases, HCN, SO2, HCl, HNSO, and CO form. Additionally, ClCN, OCCl2, HNSO2, •NSO2, and the atmospherically relevant radical •CHCl2 are also identified among the fragmentation products of CHCl2S(O)2N. The underlying mechanisms for the rearrangement and decomposition of CH2ClS(O)2N and CHCl2S(O)2N are discussed based on the experimentally-observed products and the calculated potential energy profile.
Highlights
Nitrenes R–N are neutral species containing monovalent nitrogen atoms [1]
The photolysis of CH2 ClS(O)2 N3 in solid N2 -matrix was performed by using an ArF excimer laser
Caution! Covalent azides are explosive! no explosions occurred during this work, appropriate safety precautions should be taken, especially when working with pure CH2 ClS(O)2 N3 and CHCl2 S(O)2 N3 in the condensed phase
Summary
Nitrenes R–N are neutral species containing monovalent nitrogen atoms [1]. Nitrenes are highly reactive intermediates that have been extensively used in chemical transformations such as the well-known aziridination and C–H amidation reactions, and in the covalent functionalization of nanomaterials [2,3,4]. Nitrenes R–N can be readily generated from the decomposition of azides R–N3 upon either photolysis or pyrolysis, in which molecular nitrogen is the only byproduct [5]. Due to inherent instability and high reactivity of nitrenes, the associated rapid intramolecular rearrangement and/or intermolecular reactions with solvent molecules in solution render their direct observations challenging. Molecules 2018, 23, 3312 been frequently used to probe the structure and reactivity of nitrenes [6,7]. The direct characterization of nitrenes requires either ultrafast [8,9,10] or cryogenic matrix-isolation spectroscopic methods [11,12,13]
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