Phenoxazinone Synthase-Like Activity of Binuclear Cu(II) Complexes: Correlating Ligand Electronic Effects with Catalytic Performance

Copper-containing metalloenzymes efficiently activate dioxygen, inspiring the development of biomimetic oxidation catalysts under mild conditions. This work reports the Phenoxazinone Synthase like activity of six binuclear Cu(II) complexes, belonging to the [Cu₂(bepa-R)₂](ClO₄)₂ series, in the catalytic oxidation of o-phenylenediamine (OPD) to 2,3-diaminophenazine (DAP) using dioxygen as oxidant under mild conditions. The catalytic behavior was evaluated through pH-dependent experiments, determination of kinetic order with respect to the metal complex concentration, enzymatic kinetic model fitting, hydrogen peroxide detection as reaction intermediate and thermodynamic reaction parameters estimation. All complexes catalyzed the oxidation of OPD, and the results revealed a substituent-dependent trend in catalytic performance. In particular, complexes bearing electron withdrawing groups exhibited higher turnover numbers than those containing electron-donating substituents. These findings demonstrate that electronic effects on the hydroxybenzyl moiety modulate the catalytic efficiency of the binuclear copper centers, providing insights into the design of phenoxazinone synthase-inspired oxidation catalysts.