Hydrogen peroxide production from oxygen and formic acid by homogeneous Ir–Ni catalyst

Abstract

Hydrogen peroxide was directly produced from oxygen and formic acid, catalysed by a hetero-dinuclear Ir–Ni complex with two adjacent sites, at ambient temperature. Synergistic catalysis derived from the hetero-dinuclear Ir and Ni centres was demonstrated by comparing its activity to those of the component mononuclear Ir and Ni complexes. A reaction intermediate of Ir-hydrido was detected by UV-vis, ESI-TOF-MS, and ¹H NMR spectroscopies. It was revealed that the Ir moiety serves as an active species of Ir-hydrido, reacting with oxygen to afford an Ir-hydroperoxide species through O₂ insertion, which is the rate-determining step for H₂O₂ production. Meanwhile, the Ni moiety promotes H₂O₂ formation by activating solvents as proton sources. We also found that H₂O₂ production is strongly affected by the solvent dielectric constants (DE); the highest H₂O₂ concentration was obtained in ethylene glycol with a moderate DE. The catalytic mechanism of H₂O₂ production by the Ir–Ni complex was discussed, based on kinetic analysis, isotope labelling experiments, and theoretical DFT calculations.