Extending Photocatalyst Activity through Choice of Electron Donor

Sacrificial additives are commonly employed in photoredox catalysis as a convenient source of electrons, but what occurs after electron transfer is often overlooked. Tertiary alkylamines initially form radical cations following electron transfer, which readily deprotonate to form strongly reducing,...

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Veröffentlicht in:Journal of organic chemistry 2023-05, Vol.88 (10), p.6445-6453
Hauptverfasser: Draper, Felicity, Doeven, Egan H., Adcock, Jacqui L., Francis, Paul S., Connell, Timothy U.
Format: Artikel
Sprache:eng
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Zusammenfassung:Sacrificial additives are commonly employed in photoredox catalysis as a convenient source of electrons, but what occurs after electron transfer is often overlooked. Tertiary alkylamines initially form radical cations following electron transfer, which readily deprotonate to form strongly reducing, neutral α-amino radicals. Similarly, the oxalate radical anion (C2O4 •–) rapidly decomposes to form CO2 •– (E 0 ≈ −2.2 V vs SCE). We show that not only are these reactive intermediates formed under photoredox conditions, but they can also impact the desired photochemistry, both positively and negatively. Photoredox systems using oxalate as an electron donor are able to engage substrates with greater energy demands, extending reactivity past the energy limits of single and multiphoton transition metal catalysts. Furthermore, oxalate offers better chemoselectivity than the commonly employed triethylamine when reducing substrates with moderate energy requirements.
ISSN:0022-3263
1520-6904
DOI:10.1021/acs.joc.2c02460