New dimanganese(III) complexes of pentadentate (N2O3) Schiff base ligands with the [Mn2(m-OAc)(m-OR)2]3+ core: synthesis, characterisation and mechanistic studies of H2O2 disproportionation.

HERNÁN BIAVA,; CLAUDIA PALOPOLI,; SERGIU SHOVA,; MONICA DE GAUDIO,; DAIER, VERÓNICA; GONZALEZ SIERRA, MANUEL; PIERRE TUCHAGUES, JEAN; SANDRA SIGNORELLA,

JOURNAL OF INORGANIC BIOCHEMISTRY

ELSEVIER SCIENCE INC

Año: 2006 vol. 100 p. 1660 - 1671

0162-0134

Two new diMnIII complexes [MnIII L1 ðl-AcOÞðl-MeOÞðmethanolÞ2 ŠBr (1) and [MnIII L2 ðl-AcOÞðl-MeOÞðmethanolÞðClO4 ފ (2) 2 2 (L H3 = 1,5-bis(2-hydroxybenzophenylideneamino)pentan-3-ol; L2H3 = 1,5-bis(2-hydroxynaphtylideneamino)pentan-3-ol) were synthe- sized and structurally characterized. Structural studies evidence that these complexes have a bis(l-alkoxo)(l-carboxylato) triply bridged diMnIII core in the solid state and in solution, with two substitution-labile sites – one on each Mn ion – in cis-position. The two com- plexes show catalytic activity toward disproportionation of H2O2, with saturation kinetics on [H2O2], in methanol and dimethyl formamide at 25 °C. Spectroscopic monitoring of the H2O2 disproportionation reaction suggests that (i) complexes 1 and 2 dismutate H2O2 by a mechanism involving redox cycling between MnIII and MnIV , (ii) the complexes retain the dinuclearity during catalysis, 2 2 (iii) the active form of the catalyst contains bound acetate, and (iv) protons favors the formation of inactive MnII 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. Ó 2006 Elsevier Inc. All rights reserved.