Heavy-Atom Tunneling Through Crossing Potential Energy Surfaces: Cyclization of a Triplet 2-Formylarylnitrene to a Singlet 2,1-Benzisoxazole

Nunes C. M., Viegas L. P., Wood S. A., Roque J. P. L., McMahon R. J., Fausto R.

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, vol.59, no.40, pp.17622-17627, 2020 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 59 Issue: 40
  • Publication Date: 2020
  • Doi Number: 10.1002/anie.202006640
  • Journal Name: ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Academic Search Premier, L'Année philologique, Agricultural & Environmental Science Database, Applied Science & Technology Source, Aquatic Science & Fisheries Abstracts (ASFA), CAB Abstracts, Chimica, Compendex, EMBASE, MEDLINE, Veterinary Science Database
  • Page Numbers: pp.17622-17627
  • Istanbul Kültür University Affiliated: Yes

Abstract

Not long ago, the occurrence of quantum mechanical tunneling (QMT) chemistry involving atoms heavier than hydrogen was considered unreasonable. Contributing to the shift of this paradigm, we present here the discovery of a new and distinct heavy-atom QMT reaction. Triplet syn-2-formyl-3-fluorophenylnitrene, generated in argon matrices by UV-irradiation of an azide precursor, was found to spontaneously cyclize to singlet 4-fluoro-2,1-benzisoxazole. Monitoring the transformation by IR spectroscopy, temperature-independent rate constants (k approximate to 1.4x10(-3) s(-1); half-life of approximate to 8 min) were measured from 10 to 20 K. Computational estimated rate constants are in fair agreement with experimental values, providing evidence for a mechanism involving heavy-atom QMT through crossing triplet to singlet potential energy surfaces. Moreover, the heavy-atom QMT takes place with considerable displacement of the oxygen atom, which establishes a new limit for the heavier atom involved in a QMT reaction in cryogenic matrices.