Spectroscopic Detection And Reactions Of Heteroaroyl Nitrenes And Derivatives

Carbonyl nitrenes as key reactive intermediates,have been broadly used for functionalization of carbon nanomaterials and photoaffinity labeling of biological systems.Because carbonyl nitrenes are hightly reactive,short-lived and easy to rearrange at room temperature,their structure and chemical characterization have attracted numerous attention.As a kind of ?-oxo nitrenes,the structure and reactivity of carbonyl nitrenes have been also extensively explored by experiments and quantum chemical calculations.Because of the challenge to capture reactive nitrenes,the knowledge about some novel carbonyl nitrene intermediates is limited,including the spin multiplicity and the generation of furoylnitrenes,thenoylnitrenes and difluoroacetyl nitrene.Based on unique low-temperature synthesis and matrix-isolation IR spectroscopy,we study on the decomposition of heteroaroyl azides and derivatives,carbonyl nitrenes.are detected sucessfully by IR spectroscopy.And the structure,electronic characterization,intramolecular isomerization and the decomposition of corresponding azides have been also explored by experiment and theory.In this thesis,we investigated the decomposition mechanism of furoylazides,thenoylazides and difluoroacetylazide,and photo-isomerization processes by low temperature matrix-isolation techniques.Finally,the fundamental properties of nitrenes,underlying mechanism and photochemistry in cryogenic matrices have been revealed in combination with quantum chemical calculations.1.Prior to the experimental and theoretical study,the singlet-triplet energy gaps((35)EST)in nitrenes depend strongly on the substituents.For examples,Ph C(O)N and Np C(O)N was identified as singlet species by time-resolved IR spectroscopy,matrix isolation IR spectroscopy,matrix EPR spectroscopy,and(35)EST < 0 kcal mol-1.Whereas,both NH2C(O)N and Ph O(O)N were found to have triplet ground state by matrix isolation IR spectroscopy,matrix EPR spectroscopy,and(35)EST > 0 kcal mol-1.The quantum chemical calculations predict that the(35)EST values for two furoylnitrenes will be close to zero.Therefore,two simple singlet acylnitrenes were generated through 266 nm laser photolysis of the corresponding azides.Unlike other carbonylnitrenes,both were magnetically bistable in cryogenic matrices,as evidenced by the direct observation of the singlet state with IR spectroscopy in noble matrices and the triplet state with EPR spectroscopy.We reported herein a first-time generation of two states furoylnitrenes,and fully explained this phenomenon aid of quantum chemical calculations.Upon laser irradiation,triplet 3-furylnitrene was generated from 193 nm laser photolysis of the 3-furisocyanate,which was evidenced by 15 N isotopic shift and matrix EPR spectroscopy.2.The thermal-and photo-decomposition of 2-thenoylazide and 3-thenoylazide has been studied by combining matrix-isolation IR spectroscopy and quantum chemical calculations.Upon laser irradiation(? = 266 nm),the azide eliminated N2 and furnished novel thenoylnitrenes in singlet states,which has been characterized by IR spectroscopy.Furthermore,upon subsequent UV light irradiation(? = 532 nm)the nitrenes converted to thenylisocyanate through a Curtius-type rearrangement.3-Thenylisocyanate yielded 3-thenylnitrene through 193 nm irradiation,IR spectroscopy and quantum chemical calculation demonstrated the presence of 3-thenylnitrene in triplet state.Instead,2-thenylnitrene was not observed in the laser photolysis of 2-thenylisocyanate,the experimental result was consistent with the theoretical prediction that the optimization of 2-thenylnitrene in the initially generated singlet state led directly to the ring-opened product.3.The parent difluoroacetyl azide CF2HC(O)N3 has been synthesized and characterized.The azide decomposes slowly at room temperature(300 K)into N2 and difluoromethyl isocyanate CF2 HNCO.The elusive intermediate in the stepwise Curtius-rearrangement of the azide,difluoroacetyl nitrene CF2HC(O)N,was observed by IR spectroscopy in the 193 nm laser photolysis of the azide in solid Ne matrix.Unlike other carbonylazides,flash vacuum pyrolysis(FVP)of CF2HC(O)N3 at 500 K yielded a novel carbonyl isocyanide FC(O)NC and traces of CHF2 NCO.And subsequent irradiation(193 nm)of the pyrolysis products resulted in the rearrangement of FC(O)NC to FC(O)CN.According to the quantum chemical calculations,the azide CHF2C(O)N3 prefered concerted Curtius rearrangement with minor contribution of the stepwise decomposition.The thermally generated CHF2 NCO eliminated HF and formed carbene F — C — NCO,which further undergone 1,3 fluorine shift into FC(O)NC.