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The tandem photoredox catalysis mechanism of [Ir(ppy)₂(dtb-bpy)]⁺ enabling access to energy demanding organic substrates
journal contribution
posted on 2019-11-01, 00:00 authored by Tim ConnellTim Connell, Catherine Fraser, Milena L Czyz, Zoe Smith, David HayneDavid Hayne, Egan DoevenEgan Doeven, Johnny Agugiaro, David J D Wilson, Jacqui AdcockJacqui Adcock, Andrew D Scully, Daniel E Gómez, Neil BarnettNeil Barnett, Anastasios Polyzos, Paul FrancisPaul FrancisWe report the discovery of a tandem catalytic process to reduce energy demanding substrates, using the [Ir(ppy)2(dtb-bpy)]+ (1+) photocatalyst. The immediate products of photoinitiated electron transfer (PET) between 1+ and triethylamine (TEA) undergo subsequent reactions to generate a previously unknown, highly reducing species (2). Formation of 2 occurs via reduction and semisaturation of the ancillary dtb-bpy ligand, where the TEA radical cation serves as an effective hydrogen atom donor, confirmed by nuclear magnetic resonance, mass spectrometry, and deuterium labeling experiments. Steady-state and time-resolved luminescence and absorption studies reveal that upon irradiation, 2 undergoes electron transfer or proton-coupled electron transfer (PCET) with a representative acceptor (N-(diphenylmethylene)-1-phenylmethanamine; S). Turnover of this new photocatalytic cycle occurs along with the reformation of 1+. We rationalize our observations by proposing the first example of a mechanistic pathway where two distinct yet interconnected photoredox cycles provide access to an extended reduction potential window capable of engaging a wide range of energy demanding and synthetically relevant organic substrates including aryl halides.
History
Journal
Journal of the American Chemical SocietyVolume
141Issue
44Pagination
17646 - 17658Publisher
American Chemical Society (ACS)Location
Washington, D.C.Publisher DOI
ISSN
0002-7863eISSN
1520-5126Language
engPublication classification
C Journal article; C1 Refereed article in a scholarly journalCopyright notice
2019, American Chemical SocietyUsage metrics
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