Dinuclear iron complexes based on parallel β-diiminato binding sites: syntheses, structures and reaction with O2

Abstract

With the background that certain natural systems utilize two Fe^II centres in their prosthetic groups for the activation of O₂, a ligand system containing two parallel β-diiminato binding sites linked by a xanthene backbone ([^RXanthdim]²⁻ with residues R = 2,3-dimethylphenyl and 2,4-difluorophenyl at the iminato units, respectively) was investigated with respect to its Fe^II coordination chemistry in order to study O₂activation reactions. Hence, the corresponding lithium salts were treated with FeCl₂ to yield the complexes [^Me2C6H3Xanthdim]Fe₂Cl₃(Li(thf)₃), 1 and [^F2C6H3Xanthdim]Fe₂Cl₃(Li(thf)₃), 2, respectively, each of which comprises Cl–Fe(µ-Cl)Fe–Cl(Li(thf)₃) units. 1 and 2 indeed readily react with O₂ to give the oxides[^RXanthdim]Fe₂Cl₂O containing Fe^III–O–Fe^III moieties. Due to the electron withdrawing F atoms 2 reacts more slowly than 1. The molecular structures of 1, 2 and [^Me2C6H3Xanthdim]Fe₂Cl₂O, 3, as determined by single crystal X-ray diffraction are discussed, and an investigation concerning their magnetic properties revealed an antiferromagnetic coupling of the two iron centres in all complexes; naturally, the strongest coupling is observed for 3.