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Triplet 4‐Nitrenemethyl‐Pyridine‐N‐Oxide: A Model Alkyl Nitrene Isolated in Cryogenic Matrices.

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Title: Triplet 4‐Nitrenemethyl‐Pyridine‐N‐Oxide: A Model Alkyl Nitrene Isolated in Cryogenic Matrices.
Authors: Nunes, Cláudio M.1 (AUTHOR) cmnunes@qui.uc.pt, Jesus, A. J. Lopes2 (AUTHOR), Caneca, Tatiana1 (AUTHOR), Aragay, Gemma3 (AUTHOR), Ballester, Pablo3,4 (AUTHOR), Fausto, Rui1,5 (AUTHOR)
Source: Journal of Physical Organic Chemistry. May2026, Vol. 39 Issue 5, p1-11. 11p.
Subjects: Nitrenes, Matrix isolation, Infrared spectroscopy, Pyridine oxide, Alkyl group, Quantum tunneling, Density functionals
Abstract: Alkyl nitrenes are highly reactive intermediates that are particularly challenging to study experimentally. Here, we report the first investigation of the simplest triplet alkyl nitrene bearing a pyridine‐N‐oxide moiety. Direct irradiation (λ > 350 nm) of 4‐azidomethyl‐pyridine‐N‐oxide in an Ar matrix (15 K) generated the target triplet 4‐nitrenemethyl‐pyridine‐N‐oxide 32, along with E and Z isomers of 4‐iminomethyl‐pyridine‐N‐oxide 3. Results from subsequent irradiations (λ > 325 nm) enabled the discrimination of the IR spectroscopic signatures of these species, allowing their unequivocal identification with support from DFT‐B3LYP computations. Triplet nitrene 32 was found to be stable in dark Ar matrices, demonstrating that quantum tunneling 1,2‐H shift to imine 3 is not operative on the experimental timescale. Computations show that this reaction is thermodynamically favorable on the triplet surface but involves a high‐energy barrier (~36 kcal mol−1), explaining the absence of H‐tunneling. As the pyridine‐N‐oxide moiety can act as an anchoring site for complexation with calix[4]pyrrole derivatives, our findings open new perspectives for investigating alkyl nitrene reactivity and tunneling phenomena under supramolecular confinement conditions. [ABSTRACT FROM AUTHOR]
Copyright of Journal of Physical Organic Chemistry is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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DbLabel: Engineering Source
An: 193057803
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  Data: Triplet 4‐Nitrenemethyl‐Pyridine‐N‐Oxide: A Model Alkyl Nitrene Isolated in Cryogenic Matrices.
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  Data: <searchLink fieldCode="AR" term="%22Nunes%2C+Cláudio M%2E%22">Nunes, Cláudio M.</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> cmnunes@qui.uc.pt</i><br /><searchLink fieldCode="AR" term="%22Jesus%2C+A%2E J%2E Lopes%22">Jesus, A. J. Lopes</searchLink><relatesTo>2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Caneca%2C+Tatiana%22">Caneca, Tatiana</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Aragay%2C+Gemma%22">Aragay, Gemma</searchLink><relatesTo>3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Ballester%2C+Pablo%22">Ballester, Pablo</searchLink><relatesTo>3,4</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Fausto%2C+Rui%22">Fausto, Rui</searchLink><relatesTo>1,5</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22Journal+of+Physical+Organic+Chemistry%22">Journal of Physical Organic Chemistry</searchLink>. May2026, Vol. 39 Issue 5, p1-11. 11p.
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  Data: <searchLink fieldCode="DE" term="%22Nitrenes%22">Nitrenes</searchLink><br /><searchLink fieldCode="DE" term="%22Matrix+isolation%22">Matrix isolation</searchLink><br /><searchLink fieldCode="DE" term="%22Infrared+spectroscopy%22">Infrared spectroscopy</searchLink><br /><searchLink fieldCode="DE" term="%22Pyridine+oxide%22">Pyridine oxide</searchLink><br /><searchLink fieldCode="DE" term="%22Alkyl+group%22">Alkyl group</searchLink><br /><searchLink fieldCode="DE" term="%22Quantum+tunneling%22">Quantum tunneling</searchLink><br /><searchLink fieldCode="DE" term="%22Density+functionals%22">Density functionals</searchLink>
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  Data: Alkyl nitrenes are highly reactive intermediates that are particularly challenging to study experimentally. Here, we report the first investigation of the simplest triplet alkyl nitrene bearing a pyridine‐N‐oxide moiety. Direct irradiation (λ > 350 nm) of 4‐azidomethyl‐pyridine‐N‐oxide in an Ar matrix (15 K) generated the target triplet 4‐nitrenemethyl‐pyridine‐N‐oxide 32, along with E and Z isomers of 4‐iminomethyl‐pyridine‐N‐oxide 3. Results from subsequent irradiations (λ > 325 nm) enabled the discrimination of the IR spectroscopic signatures of these species, allowing their unequivocal identification with support from DFT‐B3LYP computations. Triplet nitrene 32 was found to be stable in dark Ar matrices, demonstrating that quantum tunneling 1,2‐H shift to imine 3 is not operative on the experimental timescale. Computations show that this reaction is thermodynamically favorable on the triplet surface but involves a high‐energy barrier (~36 kcal mol−1), explaining the absence of H‐tunneling. As the pyridine‐N‐oxide moiety can act as an anchoring site for complexation with calix[4]pyrrole derivatives, our findings open new perspectives for investigating alkyl nitrene reactivity and tunneling phenomena under supramolecular confinement conditions. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Journal of Physical Organic Chemistry is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1002/poc.70074
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        Text: English
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        PageCount: 11
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      – SubjectFull: Nitrenes
        Type: general
      – SubjectFull: Matrix isolation
        Type: general
      – SubjectFull: Infrared spectroscopy
        Type: general
      – SubjectFull: Pyridine oxide
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      – SubjectFull: Alkyl group
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      – SubjectFull: Quantum tunneling
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      – SubjectFull: Density functionals
        Type: general
    Titles:
      – TitleFull: Triplet 4‐Nitrenemethyl‐Pyridine‐N‐Oxide: A Model Alkyl Nitrene Isolated in Cryogenic Matrices.
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            NameFull: Nunes, Cláudio M.
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            NameFull: Jesus, A. J. Lopes
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            NameFull: Caneca, Tatiana
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            NameFull: Aragay, Gemma
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            – D: 01
              M: 05
              Text: May2026
              Type: published
              Y: 2026
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              Value: 39
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