Non-Covalent Assembly of Proton Donors and p-Benzoquinone Anions for Co-Electrocatalytic Reduction of Dioxygen

With weak acids (AH) at high concentrations, potential inversion can occur due to favorable hydrogen-bonding interactions with the intermediate monoanion [BQ(AH)_m]^•–. The solvation shell created by these interactions can mediate a proton-coupled electron transfer at more positive potentials, resulting in an overall two electron reduction ([BQ(AH)_m]^•– + nAH + e^– ⇌ [HBQ(AH)_(m+n)-1(A)]^2–). Here we show that the resultant hydrogen-bonded [HBQ]^– adduct mediates the transfer of electrons and the proton donor 2,2,2-trifluoroethanol (TFEOH) to a Mn-based complex during the electrocatalytic reduction of dioxygen (O₂). The Mn electrocatalyst is selective for H₂O₂ with only TFEOH and O₂ present, however, with BQ present under otherwise analogous conditions, an electrogenerated [HBQ(AH)₄(A)]^2– adduct (where AH = TFEOH) alters product selectivity to 96(±0.5)% H₂O in a co-electrocatalytic fashion. These results suggest that hydrogen-bonded [HBQ]^– dianions can function in an analogous co-electrocatalytic manner to H₂Q.