Voltage-Driven Navigation of Rh(III/IV/V) Oxidation States: Unraveling Mechanistic Secrets and Selectivity in Electrochemical C–H Activation/Annulation

Electrochemically driven rhodium-catalyzed C–H bond annulation represents a promising strategy for achieving challenging transformations in organic synthesis, utilizing electrons as the sole redox reagent. However, the influence of electrochemical conditions on the reaction mechanism remains underexplored. Through computational analysis of the critical elementary steps─C–H activation, migratory insertion, β-H elimination, and reductive elimination─we delineate the distinct roles of Rh(III), Rh(IV), and Rh(V) oxidation states under electrochemical conditions. Our findings demonstrate that C–H activation is most favorable at Rh(III), while migratory insertion could occur at both Rh(III) and Rh(IV). The β-H elimination is facilitated at Rh(IV), and reductive elimination proceeds exclusively at Rh(V). Furthermore, by modulating the applied potential with a threshold of 0.96 V, the selectivity between five- and six-membered ring products can be finely controlled. These findings provide valuable mechanistic insights into transition metal catalyzed electrochemical C–H activation/annulation, offering guidance for future synthetic applications.