A Reversible Electron Relay to Exclude Sacrificial Electron Donors in the Photocatalytic Oxygen Atom Transfer Reaction with O 2 in Water

• Published in: Angewandte Chemie International Edition 2019-11, Vol.58 (45), p.16023-16027
• Main Authors: Vo, Nhat Tam, Mekmouche, Yasmina, Tron, Thierry, Guillot, Régis, Banse, Frédéric, Halime, Zakaria, Sircoglou, Marie, Leibl, Winfried, Aukauloo, Ally
• Format: Article
• Language: English
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201907337

Using light energy and O for the direct chemical oxidation of organic substrates is a major challenge. A limitation is the use of sacrificial electron donors to activate O by reductive quenching of the photosensitizer, generating undesirable side products. A reversible electron acceptor, methyl viologen, can act as electron shuttle to oxidatively quench the photosensitizer, [Ru(bpy) ] , generating the highly oxidized chromophore and the powerful reductant methyl-viologen radical MV . MV can then reduce an iron(III) catalyst to the iron(II) form and concomitantly O to O in an aqueous medium to generate an active iron(III)-(hydro)peroxo species. The oxidized photosensitizer is reset to its ground state by oxidizing an alkene substrate to an alkenyl radical cation. Closing the loop, the reaction of the iron reactive intermediate with the substrate or its radical cation leads to the formation of two oxygenated compounds, the diol and the aldehyde following two different pathways.