On the mechanism of interaction between copper (I) and O2

The mechanism of the interaction of Cu+‐α,α‐dipyridyl complex (Cu+L2) with O2 in both neutral and acid media was studied by the stopped‐flow method. The dependence of the mechanism on the acidity of the medium was established. In an acid medium H+ participated in a direct O2 reduction to HO2 by interaction with an oxygen adduct L2Cu+O2 formed without displacement of ligand molecules. In a neutral medium the reaction rate was limited by inner sphere charge transfer from Cu+ to O2 to form an oxygen “charge transfer” complex L2CuO+2. The latter interacted either with the second ion Cu+L2 or with the free ligand, or else it dissociated, reversibly or irreversibly, to form a radical anion O−2. The bimolecular rate constants of the oxygen “adduct” and “charge transfer” complex formation appeared to be kbi = (1.0 ± 0.1) × 105 and (1.5 ± 0.2) × 104M−1ċsec−1, respectively. The effective termolecular rate constants of O2 reduction to HO2 in an acid medium (with contribution from H+) and to O−2 in a neutral medium (with contribution from α,α‐dipyridyl) were kter = 2.7 × 108 and 107M−2ċsec−1. The rate constants of the elementary steps were estimated. The auto‐oxidation mechanism of the aquoion and complexes of Cu+ is discussed in terms of the results obtained.