Syntheses and Structural Characterization of Dinuclear and Tetranuclear Iron(III) Complexes with Dinucleating Ligands and Their Reactions with Hydrogen Peroxide^‡

The iron(III) complexes [Fe2(HPTB)(μ-OH)(NO3)2](NO3)2·CH3OH·2H2O (1), [Fe2(HPTB)(μ-OCH3)(NO3)2](NO3)2·4.5CH3OH (2), [Fe2(HPTB)(μ-OH)(OBz)2](ClO4)2·4.5H2O (3), [Fe2(N-EtOH-HPTB)(μ-OH)(NO3)2](ClO4)(NO3)·3CH3OH·1.5H2O (4), [Fe2(5,6-Me2-HPTB)(μ-OH)(NO3)2](ClO4)(NO3)·3.5CH3OH·C2H5OC2H5·0.5H2O (5), and [Fe4(HPTB)2(μ-F)2(OH)4](ClO4)4·CH3CN·C2H5OC2H5·H2O (6) were synthesized (HPTB = N,N,N‘,N‘-tetrakis(2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane, N-EtOH-HPTB = N,N,N‘,N‘-tetrakis(N‘ ‘-(2-hydroxoethyl)-2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane, 5,6-Me2-HPTB = N,N,N‘,N‘-tetrakis(5,6-dimethyl-2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane). The molecular structures of 2−6 were established by single-crystal X-ray crystallography. Iron(II) complexes with ligands similar to the dinucleating ligands described herein have been used previously as model compounds for the dioxygen uptake at the active sites of non-heme iron enzymes. The same metastable (μ-peroxo)diiron(III) adducts were observed during these studies. They can be prepared by adding hydrogen peroxide to the iron(III) compounds 1−6. Using stopped-flow techniques these reactions were kinetically investigated in different solvents and a mechanism was postulated.