A Recyclable Supramolecular Redox Mediator for Reductive Electrosynthesis

Redox mediators are often used in organic electrosynthesis to increase the rate of electron transfer between the electrode and substrate, allowing reactions to proceed at milder potentials and with greater selectivity. Herein, we highlight how supramolecular cages can provide unique benefits as redox mediators. Specifically, we show that tetrahedral [M₄L₆]⁸⁺ cages functionalized with redox-active perylene diimide (PDI) groups mediate the electroreduction of vicinal dihalides to the corresponding <i>trans-</i>alkenes. Relative to monomeric analogues, the cage architecture provides two key benefits. First, a greater than 2-fold rate enhancement was observed with the PDI-functionalized cage compared with a monomeric reference compound. The observed rate enhancement is attributed to the cage architecture, which limits the aggregation-induced inhibition of catalytic activity. In addition to its higher activity, the PDI cage is also fully recyclable. Due to changes in solubility upon electrochemical reduction, the cage reversibly deposits on the working electrode at the end of the reaction, allowing it to be readily recycled and reused up to five times with no loss in activity.