Tuning the Electronic Communication between Iron Carbonyl Fragments Coordinated to Bis-imine Ligands by Variation of the Bridging Unit

Abstract

The reaction of bis-imine ligands, which are synthesized from diamines containing variable bridging units between the amine functions and benzaldehyde, with Fe2(CO)9 leads to the formation of di- and tetranuclear iron carbonyl complexes. Either one or both imine moieties are coordinated to Fe2(CO)6 fragments by a C−H activation reaction in ortho-position with respect to the imine group followed by an intramolecular 1,3-hydrogen shift reaction toward the former imine carbon atom. Mossbauer spectroscopy on the tetranuclear complexes suggests that there are two slightly different types of iron atoms, both of which can be described in the oxidation state +1 with S = 1/2. Corresponding to this finding, the tetranuclear iron carbonyl compounds may be reduced four times. The cyclic voltammograms show that only the first two reduction steps, which appear at very similar potential, are fully reversible. The difference between these first two reduction potentials may be determined by a complete simulation of the cu...