The Tandem Photoredox Catalysis Mechanism of [Ir(ppy)2(dtb-bpy)]+ Enabling Access to Energy Demanding Organic Substrates

The Tandem Photoredox Catalysis Mechanism of [Ir(ppy)2(dtb-bpy)]+ Enabling Access to Energy Demanding Organic Substrates

We 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 previousl...

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Bibliographic Details
Published in:Journal of the American Chemical Society 2019-11, Vol.141 (44), p.17646-17658
Main Authors: Connell, Timothy U, Fraser, Catherine L, Czyz, Milena L, Smith, Zoe M, Hayne, David J, Doeven, Egan H, Agugiaro, Johnny, Wilson, David J. D, Adcock, Jacqui L, Scully, Andrew D, Gómez, Daniel E, Barnett, Neil W, Polyzos, Anastasios, Francis, Paul S
Format: Article
Language:eng
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Summary:We 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.
ISSN:0002-7863
1520-5126