Mediated Silane Oxidation: a practical and metal-free counter- electrode process for electrochemical reduction reactions Mickael Avanthay and Alastair J.J. Lennox University of Bristol, UK The ever-developing field of electro-organic synthetic chemistry aims to deliver transformations that are more efficient, safer and less environmentally impactful than their regular chemical-based counterparts 1 . However, every electrochemical transformation needs a counter-process happening at the opposite electrode. For oxidative reactions, proton reduction at the anode is the go-to counter-process since the formed hydrogen simply bubbles away, but there is no equivalent, broadly applicable counter-process for reduction reactions. Current approaches include the use of sacrificial anodes, various sacrificial chemical reductants or in many cases, it is simply ignored. While these may be satisfactory on some levels, the use of sacrificial metals is not ideal for sustainability and scalability reasons, and for the chemical reductants compatibility issues warrant the use of a divided cell 2 or limit how negative the potential can be applied on the cathode. 3,4 An ideal oxidative counter-process needs to be metal-free and produce soluble, reductively stable products. It should be compatible with flow chemistry and amenable to simple undivided setups such as regular Schlenk tubes or beakers. Herein we disclose an electrochemical silane oxidation which shows broad applicability as a counter-process: It was successfully applied to our recent report of a reductive hydrodefluorination of trifluoromethyl arenes 5 that previously required a divided cell, as well as other electrochemical transformations recently published by other groups that rely on sacrificial anodes. Overall, this new system for oxidative counter-processes has shown robustness in anhydrous and aqueous conditions. It is metal-free, generates no precipitate and relies on low-toxicity, stable and cheap reagents. It is a potential alternative to separators and sacrificial anodes, which is of particular interest for facilitating adaptation to flow electrochemistry and lowering the barrier of entry for electrochemistry newcomers.
References 1. Schäfer, H. J. Comptes Rendus Chim. 2011 , 14 (7–8), 745–765. 2. Wirtanen, T.; Rodrigo, E.; Waldvogel, S. R.. Adv. Synth. Catal. 2020 , 362 (11), 2088–2101. 3. Klein, M.; Waldvogel, S. R.. Angew. Chem. Int. Ed. 2022 , 61 (47). 4. Meyer, T. H.; Choi, I.; Tian, C.; Ackermann, L. Chem 2020 , 6 (10), 2484–2496. 5. Box, J. R.; Avanthay, M. E.; Poole, D. L.; Lennox, A. J. J. ACIE 2023 , 62 (12).
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