Spatio-temporal detachment of homogeneous electron transfer in controlling selectivity in mediated organic electrosynthesis
Spatio-temporal detachment of homogeneous electron transfer in controlling selectivity in mediated organic electrosynthesis
In electrosynthesis, electron transfer (ET) mediators are normally chosen such that they are more easily reduced (or oxidised) than the substrate for cathodic (or anodic) processes; setting the electrode potential to the mediator therefore ensures selective heterogeneous ET with the mediator at the electrode, rather than the substrate. The current work investigates the opposite, and counter intuitive, situation for a successful mediated electroreductive process where the mediator (phenanthrene) has a reduction potential that is negative to that of the substrate, and the cathode potential is set negative to both (Eele < EM < Es). Simulations reveal a complex interplay between mass transport, the relative concentrations of the mediator and substrate as well as the heterogeneous and homogeneous rate constants for multiple steps, which under suitable conditions, leads to separation of the homogeneous chemistry in a reaction layer detached from the electrode. Reaction layer detachment is a spatio-temporal effect arising due to opposing fluxes of the mediator radical anion M˙− and the substrate 1, which ultimately prevents 1 from reaching the electrode, thereby affording a different reaction pathway. Simulations representative of unstirred batch (1D) and flow (2D) electrolysis are presented, which qualitatively reproduce the experimental selectivity outcomes for mediated and unmediated electroreductive cyclisation of aryl iodide 1. The potential to use highly reducing homogeneous ET agents, possessing reduction potentials beyond those of the substrates, offers exciting opportunities in mediated electrosynthesis.
302-323
Hodgson, Jack W.
5c40884c-152a-4e08-a34f-47e783ebbfd7
Folgueiras Amador, Ana A.
080c345d-0a05-406a-bf7c-1939ca9c0aaa
Pletcher, Derek
f22ebe69-b859-4a89-80b0-9e190e6f8f30
Harrowven, David C.
bddcfab6-dbde-49df-aec2-42abbcf5d10b
Denuault, Guy
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Brown, Richard C.D.
21ce697a-7c3a-480e-919f-429a3d8550f5
6 June 2023
Hodgson, Jack W.
5c40884c-152a-4e08-a34f-47e783ebbfd7
Folgueiras Amador, Ana A.
080c345d-0a05-406a-bf7c-1939ca9c0aaa
Pletcher, Derek
f22ebe69-b859-4a89-80b0-9e190e6f8f30
Harrowven, David C.
bddcfab6-dbde-49df-aec2-42abbcf5d10b
Denuault, Guy
5c76e69f-e04e-4be5-83c5-e729887ffd4e
Brown, Richard C.D.
21ce697a-7c3a-480e-919f-429a3d8550f5
Hodgson, Jack W., Folgueiras Amador, Ana A., Pletcher, Derek, Harrowven, David C., Denuault, Guy and Brown, Richard C.D.
(2023)
Spatio-temporal detachment of homogeneous electron transfer in controlling selectivity in mediated organic electrosynthesis.
Faraday Discussions, 247, .
(doi:10.1039/D3FD00089C).
Abstract
In electrosynthesis, electron transfer (ET) mediators are normally chosen such that they are more easily reduced (or oxidised) than the substrate for cathodic (or anodic) processes; setting the electrode potential to the mediator therefore ensures selective heterogeneous ET with the mediator at the electrode, rather than the substrate. The current work investigates the opposite, and counter intuitive, situation for a successful mediated electroreductive process where the mediator (phenanthrene) has a reduction potential that is negative to that of the substrate, and the cathode potential is set negative to both (Eele < EM < Es). Simulations reveal a complex interplay between mass transport, the relative concentrations of the mediator and substrate as well as the heterogeneous and homogeneous rate constants for multiple steps, which under suitable conditions, leads to separation of the homogeneous chemistry in a reaction layer detached from the electrode. Reaction layer detachment is a spatio-temporal effect arising due to opposing fluxes of the mediator radical anion M˙− and the substrate 1, which ultimately prevents 1 from reaching the electrode, thereby affording a different reaction pathway. Simulations representative of unstirred batch (1D) and flow (2D) electrolysis are presented, which qualitatively reproduce the experimental selectivity outcomes for mediated and unmediated electroreductive cyclisation of aryl iodide 1. The potential to use highly reducing homogeneous ET agents, possessing reduction potentials beyond those of the substrates, offers exciting opportunities in mediated electrosynthesis.
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d3fd00089c
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Accepted/In Press date: 31 May 2023
e-pub ahead of print date: 6 June 2023
Published date: 6 June 2023
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Funding Information:
The authors acknowledge financial support from the EPSRC (Photo-Electro Programme Grant EP/P013341/1 and EP/K039466/1), and the use of the IRIDIS High Performance Computing Facility, and associated support services at the University of Southampton, in the completion of this work.
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© 2023 The Royal Society of Chemistry.
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Local EPrints ID: 481290
URI: http://eprints.soton.ac.uk/id/eprint/481290
ISSN: 0301-7249
PURE UUID: 20661582-5711-41e5-8aa6-325f18639b78
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Date deposited: 22 Aug 2023 16:45
Last modified: 30 Aug 2024 02:00
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Author:
Jack W. Hodgson
Author:
Ana A. Folgueiras Amador
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