Lewis Acid-Assisted Reduction of Nitrite to Nitric and Nitrous Oxide via the Elusive Nitrite Radical Dianion

Reduction of nitrite anions [NO2]- takes place in a myriad of environments such as in the soil as part of the biogeochemical nitrogen cycle as well as in acidified nuclear waste. Nitrite reduction typically takes place within the coordination sphere of a redox active transition metal. Lewis acid coordination, however, can dramatically modify the reduction potential of this polyoxoanion to allow for reduction under non-aqueous conditions (-0.74 V vs. NHE). This strategy enables the isolation of a borane-capped nitrite dianion [NO2]2- along with its spectroscopic study consistent with reduction to the N(II) oxidation state. Protonation of the nitrite dianion results in facile loss of nitric oxide (NO) while reaction of the nitrite dianion with nitric oxide results in disproportionation to nitrous oxide (N2O) and nitrite, connecting three redox levels in the global nitrogen cycle.