(703e) Controlling the Electron Transfer Selectivity Via Interfacial Ion Shielding Mechanism

Electrosynthesis has recently emerged as a promising tool to synthesize value-added fine chemicals and pharmaceuticals with minimal waste generation and under mild reaction conditions. Steering the direction of electron transfer among multiple electron donors/acceptors is the fundamental task in controlling the chemoselectivity in electrochemical reactions. The precise alignment of redox potentials between electrodes and substrates forms the basis for chemoselective transformations. However, to achieve direct electron transfer to/from a thermodynamically less favored target in presence of more easily reduced/oxidized functionalities, alternative mechanisms are often pursued to circumvent this thermodynamic barrier, such as hydrogen atom transfer, ligand-to-metal charge transfer, and proton-coupled electron transfer. Despite the advancements of these mechanisms, direct electron transfer remains attractive for its inherent simplicity, without the need of additional mediators or pre-functionalization compared to other pathways. However, the lack of other levers for chemoselectivity control beyond matching redox potentials restricts its broader applicability. In this talk, we would like to present a new strategy to steer the electron transfer selectivity. This strategy relies on the heterogeneous ion shielding mechanism by electrostatically adsorbing anions on the anode interface. The formed ion shielding layer imposes mass transfer limitations on the electrode interface that could block undesired molecules to approach the electrode, thus avoiding undesired side-reactions. Thus, electron transfer can selectively proceed between anode and adsorbed anions. To demonstrate the practical value of this new strategy, we developed a photoelectrochemical decarboxylative trifluoromethylation of sensitive (hetero)arenes using trifluoroacetate, an inexpensive yet relatively inert CF₃ source. An ion shielding layer, formed by trifluoroacetate anions electrostatically adsorbed on a positive WO₃ photoanode, prevents undesired electron transfer between substrates and photogenerated holes. The applicability of the developed method was demonstrated with robust photoanode stability (~380 h) and a good substrate scope. To further target practical applications, we designed and demonstrated a scaled-up photoelectrochemical flow cell with 378 cm² total electrode area, and achieved 100-gram scale trifluoromethylation of DNA base analogue in the designed flow.