Bis(μ-alkoxo)-bridged dinuclear iron(III) complexes of pyrazole-based ligands as models for iron-oxo proteins

Abstract

The synthesis and characterization of two new bis(μ-alkoxo)-bridged dinuclear iron(III) complexes with the ligands 1-(2-hydroxyethyl)-pyrazole (Hnhep) and 1-(2-hydroxyethyl)-3,5-dimethylpyrazole (Hnhed), [Fe(nhep)Cl 2(EtOH)] 2 ( 1) and [Fe(nhed)Cl 2] 2 ( 2) are reported. The crystal structures of both complexes reveal the presence of centrosymmetric dinuclear units. In compound 1, the iron(III) center has a coordination number of six, with a slightly distorted octahedral geometry. In compound 2, the bulkier nhed ligand, with methyl groups at the 3- and 5-positions of the pyrazole ring, leads to a coordination number of five at the iron(III) center in a distorted square pyramidal geometry. The magnetic properties of both complexes have been investigated in the range 2–300 K and indicate the presence of fairly weak antiferromagnetic exchange interactions between iron(III) ions ( J 1 = −10.04 cm −1 for 1 and J 2 = −12.5 cm −1 for 2). The inactivity of both complexes in the cyclohexane hydroxylation appears to be partly due to the presence of the strong iron(III)–chloride bond that does not allow exchange with the reactant molecules.