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Abstract

Herein, we describe an uncommon example of a manganese–thiolate complex, which is capable of activating dioxygen and catalyzing its two-electron reduction to generate H₂O₂. The structurally characterized dimercapto-bridged Mn^II dimer [Mn^II₂(LS)(LSH)]ClO₄ (Mn^II₂SH) is formed by reaction of the LS ligand (2,2′-(2,2′-bipyridine-6,6′-diyl)bis(1,1-diphenylethanethiolate)) with Mn^II. The unusual presence of a pendant thiol group bound to one Mn^II ion in Mn^II₂SH is evidenced both in the solid state and in solution. The Mn^II₂SH complex reacts with dioxygen in CH₃CN, leading to the formation of a rare mono-μ-hydroxo dinuclear Mn^III complex, [(Mn^III₂(LS)₂(OH)]ClO₄ (Mn^III₂OH), which has also been structurally characterized. When Mn^II₂SH reacts with O₂ in the presence of a proton source, 2,6-lutidinium tetrafluoroborate (up to 50 equiv), the formation of a new Mn species is observed, assigned to a bis-μ-thiolato dinuclear Mn^III complex with two terminal thiolate groups (Mn^III₂), with the concomitant production of H₂O₂ up to ∼40% vs Mn^II₂SH. The addition of a catalytic amount of Mn^II₂SH to an air-saturated solution of Me_nFc (n = 8 or 10) and 2,6-lutidinium tetrafluoroborate results in the quantitative and efficient oxidation of Me_nFc by O₂ to afford the respective ferrocenium derivatives (Me_nFc⁺, with n = 8 or 10). Hydrogen peroxide is mainly produced during the catalytic reduction of dioxygen with 80–84% selectivity, making the Mn^II₂SH complex a rare Mn-based active catalyst for two-electron O₂ reduction.