Electrocatalytic Multielectron Nitrite Reduction in Water by an Iron Complex

Catalytic reduction of nitrite by an iron complex in water near neutral pH to form hydroxylamine and ammonium is reported. The catalyst is an iron center coordinated by the pentadentate macrocycle 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene (FeN5H2). Catalysis is observed by cyclic voltammetry at a half-wave potential of Ep/2 = −0.98 V vs Ag/AgCl (1 M KCl) when FeN5H2, nitrite, and a buffer (pH 7.2) are present. Controlled potential electrolysis of FeN5H2 and nitrite in pH 7.2 buffer at −0.98 V produces hydroxylamine (faradaic efficiency > 90%). FeN5H2 catalyzes ammonium production by disproportionation of hydroxylamine with concomitant formation of nitrous oxide and dinitrogen. These results are a rare example of multielectron electrocatalytic nitrite reduction by an iron complex near neutral pH.