Mechanism of reduction of the nitrite ion by Cu^I complexes

The reaction of Cu_aq⁺ with NO₂^- was studied. The results are consistent with the mechanism: Cu _aq⁺ NO₂^- ⇆ (Cu ⁺NO₂^-), K = 140 ± 30 M^-1; (Cu⁺NO₂^-) + H⁺ → Cu ²⁺ + NO + OH^-, k = 4.6 × 10⁵ M ^-1S^-1. It is proposed that the copper is bound to the nitrogen in the transient complex (Cu⁺NO₂^-), In addition, the reaction was studied with (Cu^ILⁱ) ⁺ complexes. The results show that the ligands reduce the value of K and that their effect on k depends on the redox potential of the (Cu ^II/ILⁱ) couple. This reaction is the simplest model for the CuNIR (NIR = Nitric reductase) enzymes.