title: New dimanganese(III) complexes of pentadentate (N2O3) Schiff base ligands with the [Mn2(mu-OAc)(mu-OR)2]3+ core: synthesis, characterization and mechanistic studies of H2O2 disproportionation.
abstract: Two new diMn(III) complexes [Mn(2)(III)L(1)(mu-AcO)(mu-MeO)(methanol)(2)]Br (1) and [Mn(2)(III)L(2)(mu-AcO)(mu-MeO)(methanol)(ClO(4))] (2) (L(1)H(3)=1,5-bis(2-hydroxybenzophenylideneamino)pentan-3-ol; L(2)H(3)=1,5-bis(2-hydroxynaphtylideneamino)pentan-3-ol) were synthesized and structurally characterized. Structural studies evidence that these complexes have a bis(mu-alkoxo)(mu-carboxylato) triply bridged diMn(III) core in the solid state and in solution, with two substitution-labile sites--one on each Mn ion--in cis-position. The two complexes show catalytic activity toward disproportionation of H(2)O(2), with saturation kinetics on [H(2)O(2)], in methanol and dimethyl formamide at 25 degrees C. Spectroscopic monitoring of the H(2)O(2) disproportionation reaction suggests that (i) complexes 1 and 2 dismutate H(2)O(2) by a mechanism involving redox cycling between Mn(2)(III) and Mn(2)(IV), (ii) the complexes retain the dinuclearity during catalysis, (iii) the active form of the catalyst contains bound acetate, and (iv) protons favors the formation of inactive Mn(II) species. Comparison to other dimanganese complexes of the same family shows that the rate of catalase reaction is not critically dependent on the redox potential of the catalyst, that substitution of phenolate by naphtolate in the Schiff base ligand favors formation of the catalyst-substrate adduct, and that, in the non-protic solvent, the bulkier substituent at the imine proton position hampers the binding to the substrate.
authors.affiliation: Departamento de Química, Facultad de Ciencias Bioquímicas y Farmacéuticas, UNR, Suipacha 531, 2000 Rosario, Argentina.
authors.forename: Hernán
authors.initials: H
authors.lastname: Biava
authors.forename: Claudia
authors.initials: C
authors.lastname: Palopoli
authors.forename: Sergiu
authors.initials: S
authors.lastname: Shova
authors.forename: Mónica
authors.initials: M
authors.lastname: De Gaudio
authors.forename: Verónica
authors.initials: V
authors.lastname: Daier
authors.forename: Manuel
authors.initials: M
authors.lastname: González-Sierra
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Tuchagues
authors.forename: Sandra
authors.initials: S
authors.lastname: Signorella
mesh_terms: D002374:Catalase / Q000737:chemistry* / Q000378:metabolism; D015392:Chemistry, Inorganic / Q000379:methods; D004563:Electrochemistry / Q000379:methods; D004578:Electron Spin Resonance Spectroscopy; D006861:Hydrogen Peroxide / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008280:Magnetics; D008345:Manganese / Q000737:chemistry* / Q000378:metabolism; D017895:Manganese Compounds / Q000737:chemistry* / Q000378:metabolism; D000432:Methanol; D015394:Molecular Structure; D012545:Schiff Bases; D021241:Spectrometry, Mass, Electrospray Ionization; D013055:Spectrophotometry, Infrared
chemical_list: D008024:Ligands; D017895:Manganese Compounds; D012545:Schiff Bases; D008345:Manganese; D006861:Hydrogen Peroxide; D002374:Catalase; D000432:Methanol