Nitrite to nitric oxide interconversion by heme FeII complex assisted by [CuI(tmpa)]

​The present computational study complements the recent experimental efforts by Karlin and coworkers to describe the interconversion of nitrite to nitric oxide by means of an iron porphyrin complex together with a Cu chemical system, i.e., the iron(II) complex (F₈TPP)Fe^II [F₈TPP = tetrakis(2,6-difluorophenyl)porphyrinate(2−)] and a preformed copper(II)–nitrito complex [(tmpa)Cu^II(NO₂)][B(C₆F₅)₄] [tmpa = tris(2-pyridylmethyl)amine], being the latter an oxidized species of [(tmpa)Cu^I(MeCN)]⁺. By DFT calculations, we unravel how the reduction of nitrite to nitric oxide takes place through a μ-oxo heme-Fe^III–O–Cu^II complex, following a mimetic path as in the cytochrome c oxidase. Mayer bond order (MBO) and energy decomposition analyses are used to analyze the bonding strength of such nitro derivatives to either copper or iron.