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, [Mn 2 (TQA) 2 (µ-O) 2 ](ClO 4 ) 2 ( 1 ) and [Mn 2 (TQA) 2 (µ-OAc) 2 ](ClO 4 ) 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 H 2 O 2 to the complexes in 1:1 MeOH/tris-buffer solution led to rapid evolution of O 2 confirming their catalase activity. The complexes 1 & 2 exhibited turnovers of 810 and 665 mol O 2 per mol of the catalysts, respectively. Catalytic efficiencies ( k cat /K M ) 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)(ClO 4 )](ClO 4 )·MeCN ( 3 ) also exhibited similar catalase activity. The complexes ( 1 – 3 ) showed marked preference for catalytic H 2 O 2 disproportionation over oxidation of 2,2′-azinobis-(3-ethylbenzothiazoline)-6-sulfonicacid (ABTS).