Catalytic nitrite reductions by Cu II complexes containing anionic Me2 Tp, neutral Me2 Tpm, or neutral i Pr TIC ligands in the presence of l -ascorbic acid, which served as an electron donor and proton source, were investigated. The results showed that auxiliary ligands are important for copper-mediated catalytic nitrite reduction. Furthermore, the electronic effects of the ligand govern the nitrite reduction efficiency, which should be considered at two control points: one is the susceptibility of the LCu I -nitrite species to protonation and the other is the susceptibility of LCu II to reduction giving LCu I . In addition, an external strong acid leads to the production of nitrous acid, which may suggest that the reactivity of nitrous acid toward the LCu I species is a third control point. Catalytic nitrite reductions by Cu II complexes containing anionic Me2 Tp, neutral Me2 Tpm, or neutral i Pr TIC ligands in the presence of l -ascorbic acid, which served as an electron donor and proton source, were investigated.