Electrolyte induced cage effects for enantioselective electrosynthesis Zachary Nguyen, Dylan G. Boucher, Shelley D. Minteer University of Utah, USA
Electrosynthetic methods provide a tunable and green alternative to traditional organic synthetic methods by substituting traditional stochiometric redox reagents with redox activity at an electrode. However, direct electrochemical redox of organic substrates typically proceeds through planar radical intermediates preventing enantioselective transformations. A popular method of imparting enantioselectivity to electrochemical reactions is the utilization of asymmetric, redox-active transition metal catalysis, thus providing a stereoselective pathway for electroorganic reactions. Electrochemical organometallic catalytic systems are a complex intersection of a variety of fields, which leads to certain reaction parameters being oversimplified. Specifically, the electrochemical aspect of the system requires the addition of an electrolyte to increase conductivity, but their stabilizing/destabilizing effects are often overlooked. Herein, we focus on the effects of supporting electrolyte in synthetic organic electrochemistry, specifically its role in enantioselective reactions. Using cyclic voltammetry, we investigate the mechanistic impact of electrolyte identity on the key enantio-determining steps. Using a model CoSalen catalyst to carry out benzyl halide reduction, we observe changes in mechanism as the electrolyte identity and concentrations are varied. Specifically, we observe how the electrolyte identity impacts the lifetime of the chiral Co-alkyl intermediate. This Co-alkyl intermediate is especially interesting due to its ability to dissociate into its respective Co and alkyl radical species. The Co and alkyl radical can undergo radical recombination, driven by a solvent-ion cage effect formed by electrolytes and solvent. These fundamental electroanalytical studies provide a sound mechanistic basis for the origin of enantioselectivity in electroorganic reactions. In summary, these results are of a general interest as a strategy to tune and improve enantioselectivity in electrochemical transformations.
P22
© The Author(s), 2023
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