Journal
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
Volume 59, Issue 40, Pages 17622-17627Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.202006640
Keywords
heavy-atom tunneling; IR spectroscopy; matrix isolation; nitrenes; non-adiabatic transition state theory
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Funding
- FEDER, via Portugal 2020-POCI [POCI-01-0145-FEDER-028973]
- National Funds via the Portuguese Foundation for Science and Technology (FCT)
- FCT [UIDB/00313/2020, UIDP/00313/2020]
- COMPETE
- FCT
- Coimbra Chemistry Centre
- U.S. National Science Foundation [CHE-1954270, CHE-1664912]
- Fundação para a Ciência e a Tecnologia [IF/00951/2014/CP1222/CT0006, PRAXIS XXI/BD/3259/94] Funding Source: FCT
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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.
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