Spectroscopic Detection And Reaction Mechanism Of Sulfamoyl Nitrenes

As a class of versatile reactive intermediates,a-oxo nitrenes play crucial roles in chemistry,biology,and materials science.Over the past few decades,a-oxo nitrenes RC(O)N,RS(O)N,RS(O)2N,and R2P(O)N have been paid close attention by the physical organic chemistry due to their rich structrue and reactivity.As a typical type of a-oxo nitrenes,the chemical properties of alkyl,and aryl-sulfonylnitrenes has been studied in solution by using chemical trapping,ultrafast spectroscopy and quantum chemical calculations.In contrast,the highly reactive sulfamoyl nitrenes,R2NS(O)2N,have been barely investigated,although their involvement has been proposed as key intermediates in metal-catalyzed intramolecular C-H amination and aziridination with sulfamoyl azides.In this thesis,sulfamoyl azides have been synthesized based on low temperature vacuum and on-line characterization device.By combining the unique low temperature matrix-isolation spectroscopy with laser photolysis and flash vacuum pyrolysis techniques,the sulfamoyl nitrenes and the corresponding products were generated and detected.Furthermore,the properties of molecular and electronic configuration,structure and underlying reaction mechanism for the produced sulfamoyl nitrenes have been revealed in conjunction with quantum chemical calculations.The main work of this thesis includes the following two aspects1.Two sulfamoyl azides,H2NS(O)2N3 and MeN(H)S(O)2N3,have been isolated as neat substances and characterized with vibrational spectroscopy(IR and Raman).The solid-state structure of the parent molecule H2NS(O)2N3 has been established with X-ray crystallography.The thermal decomposition of both azides has been studied by combining flash vacuum pyrolysis(FVP,400?)and matrix-isolation IR spectroscopy.In addition to the complete dissociation fragments for H2NS(O)2N3(SO2,N2,and H2)and MeN(H)S(O)2N3(SO2,N2,and CH2NH),the retro-ene decomposition products HN3 and N-sulfonylamines HNSO2 and MeNSO2 form,respectively.Alternatively,quantitative yield of both N-sulfonylamines further confirmed occurs when sulfamoyl chlorides H2NS(O)2Cl and MeN(H)S(O)2Cl are used as the FVP precursors(400?).Consistent with these experimental observations,computational studies on the potential energy profiles for the decomposition of the two azides,conclusively suggest that the activation barrier of HN3-elimination through either retro-ene reaction or 1,2-elimination is ca.45 kcal mol-1,which is higer than that(ca.30 kcal mol-1)required for the direct N2-elimination to sulfamoyl nitrenes at the CCSD(T)/aug-cc-pVTZ//B3LYP/6-311++G(3df,3pd)level.The facile HCl-elimination from sulfamoyl chlorides need to surmount barriers of ca.40 kcal mol-1,which provides a safe,simple and convenient method for the gas-phase generation of N-sulfonylamines known as important reactive intermediates in synthetic chemistry.2.As the most fundamental property of sulfonylnitrenes,the energy gap between the singlet and triplet states determines the structure and reactivity.Extensive studies have been confirmed that alkyl-,aryl-,and alkoxy-sulfonylnitrenes invariably adopt the triplet ground state,despite the stabilize intromolecular interaction between the electron-deficient nitrene center and oxgen atom,which has been also observed in the closed-shell singlet states of other ?-oxo nitrenes.The molecular structures and energies of sulfamoylnitrenes R2NS(O)2N(R=H,Me)in the different spin-states were computed with second-order multiconfigurational perturbation theory CASPT2.The theory calculations predicted the sulfamoylnitrenes in the closed-shell singlet not only be stabilized by intramolecular of N…O interaction,but also intramolecular of N…N interaction.The latter situation is the lowest in energy.Two prototypical triplet sulfamoylnitrenes R2NS(O)2N(R=H,Me)were directly observed in the laser photolysis of the corresponding azides by using the matrix-isolation IR(3 K)and EPR(5 K)spectroscopy.The typical triplet signals were also confirmed by computed IR spectrum and isotopic labeling studies.The formation of the higher-energy triplet state and mechanism are reasonably explained by a change of spin from the initially generated closed-shell state through a low-energy minimum energy crossing point(MECP).