Insights into the molecular mechanism and factors affecting nitrite-to-NO transformation at transition metal sites are essential for developing sustainable technologies relevant to NO-based therapeutics, waste water treatment, and agriculture. A set of copper(II)-nitrite complexes1-4have been isolated employing tridentate pincer-type ligands (quL,pyL,ClArOL-,PhOL-) featuring systematically varied donors. Although the X-ray crystal structures of the copper(II)-nitrite cores in1-4are comparable, electrochemical studies on complexes1-4reveal that redox properties of these complexes differ due to the changes in thes-donor abilities of thephenolate / N-heterocycle based donor sites. Reactivity of these nitrite complexes with oxygen-atom-transfer (OAT) reagent (e.g. triphenyl phosphine Ph3P) and H+/e-donor reagent (e.g. substituted phenols ArOH) show the reduction of nitrite to NO gas. Detailed kinetic investigations including kinetic isotope effect (KIE), Eyring analyses for determining the activation parameters unfold that reduction of nitrite at copper(II) by Ph3P or ArOH are influenced by the CuII/CuIredox potential. Finally, this study allows mechanism driven development of catalytic nitrite reduction by ArOH in the presence of 10 mol% copper complex (1).