Syntheses and structural characterization of dinuclear and tetranuclear iron(III) complexes with dinucleating ligands and their reactions with hydrogen peroxide

The iron(III) complexes [Fe-2(HPTB)(mu -OH)(NO3)(2)](NO3)(2). CH3OH . 2H(2) O (1), [Fe-2(HPTB)(mu -OCH3)(NO3)(2)]-(NO3)(2) .4.5CH(3)OH (2), [Fe-2(HPTB) (mu -OH)(OBz)(2)](ClO4)(2).4.5H(2)O (3), [Fe-2(N-EtOH- HPTB)(mu -OH)(NO3)(2 )]-(ClO4)(NO3) . 3CH(3)OH . 1.5H(2)O (4), [Fe-2(5,6-Me-2-HPTB)(mu -OH)(NO3) (2)](ClO4)(NO3).3.5CH(3)OH .C2H5OC2H5. 0.5H(2)O (5), and [Fe-4(HPTB)(2)(mu -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-benzimidazolylmethy l) 1,3-diaminopropane, 5,6-Me-2-HPTB = N,N,N',N'-tetrakis(5,6-dimethyl-2-be nzimidazolylmethyl)-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 th e active sites of non-heme iron enzymes. The same metastable (mu -peroxo)di iron(III) adducts were observed during these studies. They can be prepared by adding hydrogen peroxide to the iron(III) compounds 1-6. Using stopped-f low techniques these reactions were kinetically investigated in different s olvents and a mechanism was postulated.