This paper reports the synthesis, structure, and mechanistic action of a Rh-based catalyst, the monohydroxide diaqua RhIII complex 1, for the direct synthesis of H2O2 from H2 and O2. Of particular interest is the elucidation of the crystal structures of 1, the low-valent RhI complex 2, the dinuclear RhII complex 3, and the peroxide RhIII complex 4 that appear in the catalytic cycle. In order to clarify the mechanistic action of the Rh-based catalyst, the catalytic reaction was investigated with 1 in water, but the possible intermediates 2–4 were isolated in organic solvents. First, we describe the synthesis, characterization, and behavior of the functioning, Rh-based catalyst. We then describe this catalytic direct synthesis of H2O2 from H2 and O2 with 1 (turnover number (TON) = 3.8 for 3 h).

Novel dry-distilled catalysts based on Rh, Ni and S were developed via a Ni(μ-S)2Rh organometallic [NiFe]hydrogenase mimic.