Lewis acid catalyzed heavy atom tunneling – the case of 1H-bicyclo[3.1.0]-hexa-3, 5-dien-2-one. Issue 33 (26th July 2021)

• Record Type: Journal Article
• Authors: Henkel, Stefan; Merini, Melania Prado; Mendez-Vega, Enrique; Sander, Wolfram
• Is Part Of: Chemical science. Volume 12:Issue 33(2021)
• Page Start: 11013
• Page End: 11019
• Publication Date: 2021-07-26
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d1sc02853g
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : The ring-opening of a highly strained cyclopropene to a carbene proceeds via heavy-atom tunneling. This rearrangement is accelerated in the presence of H2 O, ICF3 or BF3, resulting in a novel Lewis-acid catalyzed tunneling reaction. Abstract : For many thermal reactions, the effects of catalysis or the influence of solvents on reaction rates can be rationalized by simple transition state models. This is not the case for reactions controlled by quantum tunneling, which do not proceed via transition states, and therefore lack the simple concept of transition state stabilization. 1 H -Bicyclo[3.1.0]-hexa-3, 5-dien-2-one is a highly strained cyclopropene that rearranges to 4-oxocyclohexa-2, 5-dienylidene via heavy-atom tunneling. H2 O, CF3 I, or BF3 form Lewis acid–base complexes with both reactant and product, and the influence of these intermolecular complexes on the tunneling rates for this rearrangement was studied. The tunneling rate increases by a factor of 11 for the H2 O complex, by 23 for the CF3 I complex, and is too fast to be measured for the BF3 complex. These observations agree with quantum chemical calculations predicting a decrease in both barrier height and barrier width upon complexation with Lewis acids, resulting in the observed Lewis acid catalysis of the tunneling rearrangement.