Formation, Characterization And Reaction Of ?-Oxo And ?-Sulfur Nitrenes

Nitrene radicals belong to electron-deficient reactive species and are one of the important branches of free radical chemistry.As key intermediates,they participate in many reaction processes.They play important role in organic synthesis,surface modification of functional materials,biochemistry industrial catalysis and other fields.Due to the high reactivity and short lifetime of nitrenes,many researches on such species mainly focus on theoretical exploration and in situ chemical trapping reaction.However,the direct experimental investigation of their physical and chemical properties is difficult.With the prominent theoretical and applications of nitrene in many fields,the research on the structures,properties and spectrual of these species has become an urgent problem to be solved.In this thesis,a series of alpha-oxygen/sulfur substituted metastable azide and isocyanate compounds have been synthesized based on low temperature vacuum and on-line characterization device.By combining low temperature matrix isolation spectroscopy with laser photolysis and flash vacuum pyrolysis techniques,we have generated and characterized a series of alpha-oxygen/sulfur substituted nitrene intermediates.Combined with quantum chemical calculations,we have revealed their molecular and electronic structures,bonding properties,and reaction mechanisms,which will provide an important theoretical basis and scientific guidance for their potential applications.The main research contents of this thesis include the following five parts:1.The simplest alkoxycarbonylnitrene,CH₃OC?O?N,has been generated through laser?266 and 193 nm?photolysis of CH₃OC?O?N₃ and CH₃OC?O?NCO and subsequently characterized by IR(¹⁵N,D-labelling)and EPR(|D/hc|=1.66 cm^?1 and|E/hc|=0.020 cm^?1)spectroscopy in cryogenic matrices.Two conformers of the nitrene,with the CH₃ group being in syn or anti configuration to the C=O bond,have been unambiguously identified.Further UV light irradiation?365 nm?of the nitrene results in isomerization to CH₃ONCO,completing the frequently explored mechanism for the Curtius rearrangement of CH₃OC?O?N₃.2.As the prototype Curtius rearrangement reaction,carbamoyl azide decomposes into aminoisocyanate and molecular nitrogen.However,the key intermediate carbamoylnitrene was previously undetected,even though the decomposition of carbamoyl azides has been studied frequently since its discovery in the 1890s.Upon ArF laser??=193 nm?photolysis,the stepwise decomposition of the two simplest carbamoyl azides H₂NC?O?N₃ and Me₂NC?O?N₃,isolated in solid noble gas matrices,occurs with the formation of the corresponding carbamoylnitrenes H₂NC?O?N and Me₂NC?O?N.Both triplet species are characterized for the first time by combining matrix-isolation IR spectroscopy and quantumchemical calculations.Subsequent visible-light irradiations cause efficient rearrangement of these nitrenes into the respective aminoisocyanates.3.The high-energy carbonyl azide OC?N₃?₂ easily decompose into CO and N₂ at room temperature.To account for the formation of the various decomposition intermediates of OC?N₃?₂ reported in the literature,we used the DFT method to analyze the decomposition potential energy surface of OC?N₃?₂ in detail.The theoretical calculation results show that before OC?N₃?₂ generates the important intermediate cyclo-N₂CO in the thermal decomposition process,the singlet carbonyl nitrene species OC?N₃?N is firstly produced,and then it releases to the lower triplet state through intersystem crossing,then OC?N₃?N decomposes cyclo-N₂CO and N₂ in a concerted pathway.The decomposition barrier of cyclo-N₂CO is nearly 25 kcal mol^?1,which makes it detectable.The singlet nitrene OC?N₃?N can also undergo intramolecular rearrangement to generate a open-chain high-energy polynitrogen molecule NNNNCO,which generates CO and N₂ through concerted pathway.4.Thiophosphoryl nitrenes,R₂P?S?N,are thiazirine-like intermediates that have been chemically inferred from trapping products in early solution studies.In this work,photolysis of the simplest thiophosphoryl azide,F₂P?S?N₃,in solid noble-gas atrices enabled a firsttime spectroscopic?IR and UV-vis?identification of the thiophosphoryl nitrene F₂P?S?N in its singlet ground state.Upon visible-light irradiation??495 nm?,it converts into the thionitroso isomer F₂PN=S,which can also be produced in the gas phase from flash vacuum pyrolysis of F₂P?S?N₃.Further irradiation of F₂PN=S with 365nm UV light leads to the reformation of F₂P?S?N and isomerization to the thiazyl species F₂PS?N.5.The novel aromatic ring compound 2,4-diphospha-3,5-diaza-thiole?cyclo-SNPNP?was synthesized via flash pyrolysis of SP?N₃?₃ and characterized by IR spectroscopy and ¹⁵N isotope labeling.Quantum chemical computations indicate its formation by head-to-tail dimerization of SNP and subsequent elimination of a sulfur atom from the highlyunstable boatlike six-membered-ring compound cyclo-SNPSNP.