81305-65-9Relevant academic research and scientific papers
Photochemistry of 2-Formylphenylnitrene: A Doorway to Heavy-Atom Tunneling of a Benzazirine to a Cyclic Ketenimine
Nunes, Cláudio M.,Reva, Igor,Kozuch, Sebastian,McMahon, Robert J.,Fausto, Rui
, p. 17649 - 17659 (2017)
The slippery potential energy surface of aryl nitrenes has revealed unexpected and fascinating reactions. To explore such a challenging surface, one powerful approach is to use a combination of a cryogenic matrix environment and a tunable narrowband radiation source. In this way, we discovered the heavy-atom tunneling reaction involving spontaneous ring expansion of a fused-ring benzazirine into a seven-membered ring cyclic ketenimine. The benzazirine was generated in situ by the photochemistry of protium and deuterated triplet 2-formylphenylnitrene isolated in an argon matrix. The ring-expansion reaction takes place at 10 K with a rate constant of ～7.4 × 10-7 s-1, despite an estimated activation barrier of 7.5 kcal mol-1. Moreover, it shows only a marginal increase in the rate upon increase of the absolute temperature by a factor of 2. Computed rate constants with and without tunneling confirm that the reaction can only occur by a tunneling process from the ground state at cryogenic conditions. It was also found that the ring-expansion reaction rate is more than 1 order of magnitude faster when the sample is exposed to broadband IR radiation.
Photochemical Generation of Benzoazetinone by UV Excitation of Matrix-Isolated Precursors: Isatin or Isatoic Anhydride
Lapinski, Leszek,Nowak, MacIej J.,Rostkowska, Hanna
, p. 4106 - 4114 (2020/06/19)
Benzoazetinone was photochemically generated by UV irradiation of isatin isolated in low-temperature Ar matrixes. Upon UV (λ = 278 nm) excitation of isatin, monomers of the compound underwent decarbonylation and the remaining part of the molecule adopted the benzoazetinone structure or the structure of its open-ring isomer α-iminoketene. The same products (benzoazetinone and α-iminoketene) were generated by UV (λ = 278 nm) induced decarboxylation of matrix-isolated monomers of isatoic anhydride. Photoproduced α-iminoketene appeared in the low-temperature matrixes as a mixture of syn and anti isomers. Photoproducts generated upon λ = 278 nm irradiation of matrix-isolated isatin were subsequently exposed to λ = 532 nm light. That irradiation resulted in the shift of the α-iminoketene-benzoazetinone population ratio in favor of the latter closed-ring structure. The next irradiation at 305 nm caused the shift of the α-iminoketene-benzoazetinone population ratio in the opposite direction, that is, in favor of the open-ring isomer. Neither benzoazetinone nor its α-iminoketene open-ring isomer was generated upon UV (λ = 278 nm) irradiation of phthalimide isolated in Ar matrixes. Instead, the UV-excited monomers of this compound underwent such phototransformations as oxo → hydroxy phototautomerism or degradation of the five-membered ring with release of HNCO and CO. The efficiency of these photoconversions was low.
Evidence of a Nitrene Tunneling Reaction: Spontaneous Rearrangement of 2-Formyl Phenylnitrene to an Imino Ketene in Low-Temperature Matrixes
Nunes, Cláudio M.,Knezz, Stephanie N.,Reva, Igor,Fausto, Rui,McMahon, Robert J.
, p. 15287 - 15290 (2016/12/09)
Triplet 2-formyl phenylnitrene was generated by photolysis of 2-formyl phenylazide isolated in Ar, Kr, and Xe matrixes and characterized by IR, UV-vis, and EPR spectroscopies. Upon generation at 10 K, the triplet nitrene spontaneously rearranges in the dark to singlet 6-imino-2,4-cyclohexadien-1-ketene on the time scale of several hours. The intramolecular [1,4] H atom shift from the nitrene to the imino ketene occurs by tunneling, on the triplet manifold, followed by intersystem crossing. This case constitutes the first direct evidence of a tunneling reaction involving a nitrene.
