Electrochemical Reduction of 4-Nitrobenzyl Phenyl Thioether for Activation and Capture of CO₂

In this work, a new simple molecule, 4-nitrobenzyl phenyl thioether (1), is prepared and used for controlling and tuning CO ₂ reactivity in function of the electrode potential. The first part of the study is devoted to determining the electrochemical reduction mechanism of 1 in N,N-dimethylformamide under nitrogen. The compound shows a first reversible one-electron transfer process, whereas the reaction cleavage of the C−S bond takes place after a second electron transfer process through a stepwise mechanism (thermodynamic and kinetic parameters are conveniently determined). In the second part of the study, the inert atmosphere was replaced by a CO ₂ atmosphere. At low potential values, compound 1 acts as a redox mediator that allows the reduction of CO ₂ at ca. −1.2 V vs. SCE. The electrochemical generation of 1 ²⁻ at more negative potential values leads to a C−S bond cleavage reaction that yields the corresponding nitrobenzyl and thiosulfate anions, which react with CO ₂. The nitro aromatic anion derivative makes it possible to obtain electrocarboxylated derivatives, whereas the thiophenolate anion captures CO ₂ reversibly. Hence, this research opens a new way of tuning and controlling the reaction processes associated with CO ₂ from homogenous catalysis at low negative potentials, to electrocarboxylation processes passing to CO ₂ reversible electrochemically triggered adsorption processes.