Reduction of nitrite anions (NO2−) to nitric oxide (NO), nitrous oxide (N2O) and ultimately dinitrogen (N2) takes place in a variety of environments, including in the soil as part of the biogeochemical nitrogen cycle and in acidified nuclear waste. Nitrite reduction typically takes place within the coordination sphere of a redox-active transition metal. Here we show that Lewis acid coordination can substantially modify the reduction potential of this polyoxoanion to allow for its reduction under non-aqueous conditions (−0.74 V versus NHE). Detailed characterization confirms the formation of the borane-capped radical nitrite dianion (NO22−), which features a N(II) oxidation state. Protonation of the nitrite dianion results in the facile loss of nitric oxide (NO), whereas its reaction with NO results in disproportionation to nitrous oxide (N2O) and nitrite (NO2−). This system connects three redox levels in the global nitrogen cycle and provides fundamental insights into the conversion of NO2− to NO.
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Crystallographic data for the structures reported in this Article have been deposited at the Cambridge Crystallographic Data Centre, under deposition numbers CCDC 2074366 (1), 2074367 (2), 207468 (3), 2074369 (4), 2074370 (5), 2074371 (6) and 2074372 (7). Copies of the data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/. All other data supporting the findings of this study are available within the Article and its Supplementary Information.
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This work was supported by the NIH (P41GM103521 to J.H.F., R35GM124908 to K.M.L. and R01GM126205 to T.H.W.). XAS data were obtained at SSRL, which is supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under contract no. DE-AC02-76SF00515. The SSRL Structural Molecular Biology Program is supported by the Department of Energy’s Office of Biological and Environmental Research and by NIH/NIGMS (including P41GM103393). The work at SSRL was also supported by the US Department of Energy Office of Basic Energy Sciences (proposal no. 100487).
The authors declare no competing interests.
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Synthesis, characterization and computational details, Figs. 1–42, schemes 1–5 and computational coordinates.
Crystallographic data for compound 1; CCDC 2074366.
Crystallographic data for compound 2; CCDC 2074367.
Crystallographic data for compound 3; CCDC 2074368.
Crystallographic data for compound 4; CCDC 2074369.
Crystallographic data for compound 5; CCDC 2074370.
Crystallographic data for compound 6; CCDC 2074371.
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Hosseininasab, V., DiMucci, I.M., Ghosh, P. et al. Lewis acid-assisted reduction of nitrite to nitric and nitrous oxides via the elusive nitrite radical dianion. Nat. Chem. 14, 1265–1269 (2022). https://doi.org/10.1038/s41557-022-01025-9