Synthesis and properties of diiron complexes with heteroaromatic linkers: An approach for modulation of organometallic molecular wire

Metal complexes with two redox active organometallic Cp∗(dppe)Fe C C units bridged with N-methylpyrrole (3), furan (4) and dipyrrolylethene (6) have been synthesized and characterized by 1H and 31P NMR, IR and ESI-MS spectroscopy as well as X-ray diffraction study (for 3). Cyclic voltammograms of 3 and 4 show two reversible redox waves ascribed to iron centered redox processes, and the comproportionation constants (KC) of their mixed valence species were determined to be 5.8 × 106 and 1.0 × 106, respectively. UV–Vis–NIR spectra of 3+ and 4+ contain intense absorption bands in the NIR region ascribed to intervalence charge transfer processes. The complexes with electronic coupling (Vab) values of 2950 (3) and 2665 cm−1 (4) were classified as class III compounds according to the Robin–Day classification. These data suggest that the electronic interaction between the two iron centers is stronger than those of the p-phenylene and thienylene derivatives. Complex 6, a pyrrole analogue of the photochromic dithienylethene complexes, turns out not to show photochromic behavior, indicating that the heteroaromatic component influenced significantly on photochromic behavior.