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.