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

Abstract

Abstract 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-hydroxypropane-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.