Spectroscopic Detection And Reactivity Of Sulfonyl Nitrenes

Nitrenes(R-N)are neutral species containing monovalent nitrogen atoms.As the highly reactive intermediates,nitrenes have been broadly used in organic synthesis,the covalent functionalization of nanomaterials and photolabeling of biomolecules.In the recent few decades,their spectroscopic detection,molecular structures and reaction mechanisms have attracted close attention from experimental and theoretical studies.Due to extreme unstability at room temperature,the capture and direct observation of nitrenes require sophisticated methods such as ultrafast time-resolved spectroscopy and cryogenic matrix-isolation spectroscopy.Herein,the heteroaryl sulfonyl nitrenes(2-and 3-thienylsulfonyl nitrenes)and alkyl sulfonyl nitrenes(chloro-and dichloro-methylsulfonyl nitrenes)were studied by matrix-isolation IR and EPR spectroscopy,high flash vacuum pyrolysis as well as quantum chemical calculations.Their spectra,ground state multiplicity,molecular structures and decompositions are reported systematically.The main work includes the following two aspects.1.2-Thienylsulfonyl azide and 3-thienylsulfonyl azide have been prepared and spectroscopically characterized.During the 266 nm laser irradiation,both azides split off molecular nitrogen and generate the corresponding thienylsulfonyl nitrene intermediates in solid Ne(2.8 K),Ar(10 K)and N2(15 K)matrices.Upon subsequent UV-light(365 nm)irradiation,no Curtius-rearrangement but decomposition of 2-thienylsulfonyl nitrene occurs by SO2-elimination and the concurrent formation of ring-opening product(s-Z)-4-thioxo-2-butenenitrile.While,violet-light irradiation(400±20 nm)of 3-thienylsulfonyl nitrene causes SO2-elimination to yield 3-thienylnitrene in the triplet ground state.3-Thienylnitrene not only combines with SO2 to furnish 3-thienyl-N-sulfonylamine but also undergoes ring-opening to(s-E)-4-thioxo-2-butenenitrile under the UV-light irradiation(365 nm).The identification of these new species with IR spectroscopy is supported by 15N-labeling experiments and theoretical calculations.The triplet ground-state multiplicity of two thienylsulfonyl nitrenes has been confirmed by matrix-isolation EPR spectra and the mechanisms for their generation in stepwise decomposition of corresponding azides are disclosed by quantum chemical calculations.2.Chloro-and dichloro-methylsulfonyl nitrenes,CH2CIS(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.Upon subsequent UV light irradiation(365 nm),both sulfonyl nitrenes RS(O)2N(R=CH2Cl and CHCl2)undergo 1,2-R shift to N-sulfonlyamines RNSO2 and 1,2-oxygen shift to S-nitroso compounds RS(O)NO in solid N2-matrice at 15 K.Under the condition of flash vacuum pyrolysis at 600 K,CH2CIS(O)2N3 dissociates completely to yield HCN,SO2,HCl,HNSO and CO with extrusion of molecular nitrogen.However,·NSO2,·CHCl2,SO2,HCl,HCN,ClCN and OCCl2 have been identified among the decomposition products of CHCl2S(O)2N3 at 700 K.The flash vacuum pyrolysis of CHC12S(O)2N3 provides an efficient and practical method for the gas-phase generation of atmospherically relevant radical·CHC12.With the aid of quantum chemical calculations and 15N-labeling experiments,the matrix-isolation IR(15 K)and EPR(5 K)spectra for triplet CH2ClS(O)2N and CHCl2S(O)2N have been analyzed.In the mean time,the underlying mechanisms for the decomposition and rearrangement of CH2ClS(O)2N and CHCl2S(O)2N are discussed based on the experimentally-observed products and calculated potential energy profiles.