Lewis acid-assisted reduction of nitrite to nitric and nitrous oxides via the elusive nitrite radical dianion

Abstract

VH and THW conceived the synthetic approach; VH carried out synthetic experiments; VH and PG performed electrochemical measurements; VH and JAB performed crystallographic analysis; IMD, CJT, and DN collected XAS data, KML, and SC collected EPR data, IMD and KML carried out electronic structure calculations and interpreted spectroscopic data, VH, KML, and THW wrote the manuscript with assistance by JHF.

NO and N2O Release from the Trityl Diazeniumdiolate Complexes [M(O2N2CPh3)3]− (M = Fe, Co)

“…To rationalize this observation, we suggest that the redox active metal can scavenge the hyponitrite radical anion, [ONNO] · – , by converting it into [ONNO] 2– . [ONNO] · – is a plausible intermediate in the reaction (formed by C–N bond homolysis), and a species that is known to react rapidly with NO. − …”

“…Given these results, we sought to improve the yields of NO by ligation of the trityl diazeniumdiolate to a redox-active metal, which we hypothesized could intercept potential NO-scavenging intermediates generated during the reaction. One such intermediate, [ONNO] · – , is known to react rapidly with NO to form N 2 O and NO 2 – . − Herein, we report the synthesis and characterization of two transition metal trityl diazeniumdiolate complexes, namely, [K­(18-crown-6)]­[M­(O 2 N 2 CPh 3 ) 3 ] (M = Co, Fe), as well as their response to photolytic and oxidative stimuli.…”

Enhancement of Ammonium Oxidation at Microoxic Bioanodes

“…It is postulated that the primary formation of N 2 O occurs during the process of NH 2 OH oxidation. Nitrifier denitrification, involving NO 2 – reduction by nitrifiers, is less likely under the observed anode potentials (0.52–0.55 V vs Ag/AgCl), which are considerably higher than the theoretical reduction potential of NO 2 – to NO (0.17 V vs Ag/AgCl at pH = 7) . The fact that NH 2 OH addition enhances NH 4 + oxidation is related to the conversion pathways.…”

“…While a microoxic level of oxygen was present, small amounts of NO − reduction by nitrifiers, is less likely under the observed anode potentials (0.52−0.55 V vs Ag/AgCl), which are considerably higher than the theoretical reduction potential of NO 2 − to NO (0.17 V vs Ag/AgCl at pH = 7). 36 The fact that NH 2 OH addition enhances NH 4 + oxidation is related to the conversion pathways. In the presence of oxygen, NH + oxidation rate.…”

Insights into Single-Electron-Transfer Processes in Frustrated Lewis Pair Chemistry and Related Donor–Acceptor Systems in Main Group Chemistry

“…Recently, Warren et al presented the reduction of the nitrite anion using strong Lewis acids, such as B­(C 6 F 5 ) 3 , without breaking any N–O bonds (Scheme ). The unsymmetrically capped [Cp* 2 Co]­[(C 6 F 5 ) 3 B–ONO] ( 77 ) was produced by adding 1 equiv of B­(C 6 F 5 ) 3 and [Cp* 2 Co]­[NO 2 ] ( 76 ) in fluorobenzene and showed the B­(C 6 F 5 ) 3 bound to one of the O-atoms of nitrite with distinctly different N–O distances of 1.337(10) Å (for capped O atom) and 1.200(10) Å (free O atom), respectively . Addition of a second equivalent of B­(C 6 F 5 ) 3 in fluorobenzene forms the doubly activated nitrite anion [Cp* 2 Co]­[(C 6 F 5 ) 3 B–ONO–B­(C 6 F 5 ) 3 ] ( 78 ) with symmetric NO distances (1.261(2), 1.225(2)­Å), indicating the coordination of the Lewis acid to both O atoms.…”