High Activities of Hydrogen Peroxide Decomposition Catalyzed by Dinuclear Schiff Base Mn(III)-Cu(II) Complexes Accompanying Metal Substitution in N,N-Dimethylformamide and the Crystal Structure of a Substituted Schiff Base Cu(II) Complex

Article abstract of DOI:10.1246/bcsj.71.1081

The effects of divalent metal ions (M²⁺=Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ ions) on the catalase-like activities of mononuclear Schiff base Mn(III) complexes, such as [Mn(salen)Cl] (H₂salen: N,N'-ethylenebis(salicylideneamine)), [Mn(saltn)Cl] (H₂saltn: N,N'-propane-1,3-diylbis(salicylideneamine)), [Mn(saltnOH)Cl] (H₂saltnOH: N,N'-(2-hydroxy- propane-1,3-diyl)bis(salicylideneamine)), and [Mn(saltnOCOPh)Cl] (H₂saltnOCOPh: N,N'-(2-benzoyloxypropane-1,3- diyl)bis(salicylideneamine)), in N,N'-dimethylformamide (DMF) have been reported. Except for the Cu²⁺ ion, H₂O₂ decomposition was depressed in the presence of M²⁺ = Mn²⁺, Co²⁺, Ni²⁺, and Zn²⁺ ions because [Mn(salen)]⁺ reacted with M²⁺ to give dinuclear Mn(III)-M(II) and trinuclear Mn(III)₂-M(II) complexes inactive toward H₂O₂ in DMF. For the Cu²⁺ ion, the dinuclear complexes with the salen and saltnOCOPh ligands showed high activities, although the trinuclear complexes were inactive toward H₂O₂. The ESR spectra suggested that the intramolecular electron transfer from Cu(II) to Mn(III) on the dinuclear Mn(III)-Cu(II) complex partly occurs to produce a dinuclear Mn(II)-Cu(III) complex active toward H₂O₂. During H₂O₂ decomposition including the radical reaction path, [Cu(salR)] (R = en, tnOCOPh) and Mn²⁺ were produced accompanying metal substitution by Cu²⁺ on the dinuclear complex. To clarify the substituted product, the preparation and an X-ray crystal structure analysis of [Cu(saltnOCOPh)] were carried out. Three independent [Cu- (saltnOCOPh)] complexes (CuA, CuB, and CuC) were present along with an intermolecular π-π stacking interaction between benzene rings on the salicylidenediamine moiety and benzene ring on the benzoyloxy group in the crystal. The geometries around the coppers in both CuA and CuC are more distorted toward tetrahedral from square plane than that in CuB. No stacking interaction between benzene rings on [Cu(saltnOCOPh)] occurs in DMF solution.