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.

doi:10.1021/jacs.6b07368

Cited by 56 publications

(85 citation statements)

References 47 publications

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“…Thet riplet 2-formylnitrene (54 a)r earranged in the dark to the singlet ketene 55 a on at ime scale of several hours at 10 K( Scheme 13). [55] Here,t hree processes are involved:tunneling,rearrangement, and intersystem crossing (ISC).…”

Section: Tunneling In Nitrene Reactionsmentioning

confidence: 99%

Carbenes and Nitrenes: Recent Developments in Fundamental Chemistry

Wentrup

2018

Angew Chem Int Ed

127

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Carbenes and nitrenes can exist in both singlet and triplet states, sometimes equally stable and interconverting either thermally or photochemically. Many carbene and nitrene reactions proceed via tunneling at low temperatures. Numerous singlet and triplet states have been characterized spectroscopically, and a detailed understanding of the chemical and physical properties of carbenes and nitrenes is emerging. There has been significant progress in the direct observation of carbenes, nitrenes, and many other reactive intermediates in recent years through the application of matrix photolysis and flash vacuum pyrolysis linked with matrix isolation at cryogenic temperatures. Our understanding of singlet and triplet states has improved through the interplay of spectroscopy and computations. Bistable carbenes and nitrenes as well as many examples of tunneling have been discovered and numerous rearrangements and fragmentations have been documented. The correlation of the zero-field splitting parameter D with calculated spin densities on nitrenes and carbenes is discussed. This Minireview gives an overview of some of these developments.

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Section: Tunneling In Nitrene Reactionsmentioning

confidence: 99%

Carbenes and Nitrenes: Recent Developments in Fundamental Chemistry

Wentrup

2018

Angew Chem Int Ed

127

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“…This interpretation is strongly supported by a close match between the spectral positions of the lower-wavenumbers bands (2111 and 2114 cm –1 ) and the wavenumber (2110 cm –1 ) at which a band of iminoketene-2 was previously observed. 25 Small differences between the wavenumbers given above are easily understandable, taking into account the presence of different partners (CO, CO 2 , and N 2 ) in the same matrix cage with the in situ generated iminoketene product.…”

Section: Resultsmentioning

confidence: 99%

Photochemical Generation of Benzoazetinone by UV Excitation of Matrix-Isolated Precursors: Isatin or Isatoic Anhydride

2020

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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.

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“…In contrast to the frequently observed tunneling transformations in the analogous carbenes, tunneling in nitrenes is scarcely known. Recently, a first example of hydrogen tunneling reaction has been observed in the rearrangement from 2‐formyl phenylnitrene to an imino ketene in cryogenic matrices …”

Section: Methodsmentioning

confidence: 99%