Experimental, Simulation, and Computational Study of the Interaction of Reduced Forms of N-Methyl-4,4’-Bipyridinium with CO₂

N-methyl-4,4’-bipyridinium (Mebipy⁺) can be reduced in two separate one-electron steps in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPTFSI). The first reduction product Mebipy, a radical species, is shown to have no significant interaction with dissolved CO₂. In contrast, the second reduction product, Mebipy⁻, forms an adduct with CO₂. This adduct has a relatively strong C−N bond from nucleophilic interaction of the non-quaternized nitrogen of the anion with the electrophilic carbon of CO₂. These interactions are characterized using density functional theory (DFT). During electrochemical reduction of Mebipy⁺ in the presence of dissolved CO₂, this strong interaction of Mebipy⁻ drives a disproportionation reaction in which two Mebipy radicals react to produce Mebipy⁺ and Mebipy⁻, which subsequently reacts with CO₂ to form the nitrogen-bound adduct, Mebipy-CO₂ ⁻, a type of carbamate. This electrochemical DISP mechanism is simulated, providing a good fit with experimental results. The overall stoichiometry for the electrochemical capture and release of CO₂ in this system is that two electrons are required to bind one equivalent of CO₂.