Photochemistry of 2-Formylphenylnitrene: A Doorway to Heavy-Atom Tunneling of a Benzazirine to a Cyclic Ketenimine

Cláudio M. Nunes, Igor Reva, Sebastian Kozuch, Robert J. McMahon, Rui Fausto

Research output: Contribution to journalArticlepeer-review

35 Scopus citations


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.

Original languageEnglish
Pages (from-to)17649-17659
Number of pages11
JournalJournal of the American Chemical Society
Issue number48
StatePublished - 6 Dec 2017

ASJC Scopus subject areas

  • Catalysis
  • Chemistry (all)
  • Biochemistry
  • Colloid and Surface Chemistry


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