Synthesis, structures and catalase activities of bis(μ-oxo)diMnIII,III and bis(μ- acetato)diMnII,II complexes bearing a quinolyl donor tripod ligand

Abstract

The syntheses and characterization of two new complexes, [Mn2(TQA)2(µ-O)2](ClO4)2 (1) and [Mn2(TQA)2(µ-OAc)2](ClO4)2 (2) (TQA = tris(2-quinolylmethyl)amine), are described. The diMn complexes (1 & 2) have been characterized by elemental analysis, IR and X-ray diffraction. The complexes partly resemble the active-site structures of the oxidized and reduced forms of bacterial manganese catalases. Addition of aqueous H2O2 to the complexes in 1:1 MeOH/tris-buffer solution led to rapid evolution of O2 confirming their catalase activity. The complexes 1 & 2 exhibited turnovers of 810 and 665 mol O2 per mol of the catalysts, respectively. Catalytic efficiencies (kcat/KM) of 8.5 and 22 M−1 s−1 were measured for the complexes 1 & 2. The corresponding mononuclear Mn(II) complex, [Mn(TQA)(MeCN)(ClO4)](ClO4)·MeCN (3) also exhibited similar catalase activity. The complexes (1–3) showed marked preference for catalytic H2O2 disproportionation over oxidation of 2,2′-azinobis-(3-ethylbenzothiazoline)-6-sulfonicacid (ABTS).