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


Nunes C. M., Reva I., Kozuch S., McMahon R. J., Fausto R.

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, vol.139, no.48, pp.17649-17659, 2017 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 139 Issue: 48
  • Publication Date: 2017
  • Doi Number: 10.1021/jacs.7b10495
  • Journal Name: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.17649-17659
  • Istanbul Kültür University Affiliated: Yes

Abstract

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,similar to 7.4 x 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.