Dinuclear iron complexes based on parallel beta-diiminato binding sites: syntheses, structures and reaction with O-2

With the background that certain natural systems utilize two FeII centres in their prosthetic groups for the activation of O-2, a ligand system containing two parallel beta-diiminato binding sites linked by a xanthene backbone ([(R)Xanthdim](2-) with residues R = 2,3-dimethylphenyl and 2,4-difluorophenyl at the iminato units, respectively) was investigated with respect to its FeII coordination chemistry in order to study O2 activation reactions. Hence, the corresponding lithium salts were treated with FeCl2 to yield the complexes [(Me2C6H3)Xanthdim]Fe2Cl3(Li(thf)(3)), 1 and [(F2C6H3)Xanthdim] Fe2Cl3(Li(thf)(3)), 2, respectively, each of which comprises Cl-Fe(mu-Cl)Fe-Cl(Li(thf)(3)) units. 1 and 2 indeed readily react with O-2 to give the oxides [(R)Xanthdim]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 [(Me2C6H3)Xanthdim] 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.