Département de chimie moléculaire

Herein, we describe an uncommon example of a manganese-thiolate complex, which is capable of activating dioxygen and catalyzing its two-electron redn. to generate H2O2. The structurally characterized dimercapto-bridged MnII dimer [MnII2(LS)(LSH)]ClO4 (MnII2SH) is formed by reaction of the LS ligand (2,2'-(2,2'-bipyridine-6,6'-diyl)bis(1,1-diphenylethanethiolate)) with MnII. The unusual presence of a pendant thiol group bound to one MnII ion in MnII2SH is evidenced both in the solid state and in soln. The MnII2SH complex reacts with dioxygen in CH3CN, leading to the formation of a rare mono-$μ$-hydroxo dinuclear MnIII complex, [(MnIII2(LS)2(OH)]ClO4 (MnIII2OH), which has also been structurally characterized. When MnII2SH 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 obsd., assigned to a bis-$μ$-thiolato dinuclear MnIII complex with two terminal thiolate groups (MnIII2), with the concomitant prodn. of H2O2 up to ∼40{%} vs MnII2SH. The addn. of a catalytic amt. of MnII2SH to an air-satd. soln. of MenFc (n = 8 or 10) and 2,6-lutidinium tetrafluoroborate results in the quant. and efficient oxidn. of MenFc by O2 to afford the resp. ferrocenium derivs. (MenFc+, with n = 8 or 10). Hydrogen peroxide is mainly produced during the catalytic redn. of dioxygen with 80-84{%} selectivity, making the MnII2SH complex a rare Mn-based active catalyst for two-electron O2 redn. [on SciFinder(R)]