Ligand bridged heterodinuclear transition metal complexes - Syntheses, structures and electrochemical investigations

The syntheses of the homo- and hererobimetallic compounds [(LnM)-M-I(eta(5)-C5H4)Fe(eta(5)-C9H6)(2) MLn] (2a-5d), [(C9H7)CMe2(eta(5)-C5H4)Fe(eta(5)-C5H4)CMe2(eta(5)-C9H6)(2) MLn] (6a-c), and [(eta(5)-C5H4)CMe2(eta(5)-C9H6)(2)MLn](2)Fe (7a-b) are reported with (MLn)-M-I = Rh(cod) 2, Ir(cod) 3, Mn(CO)(3) 4 and FeCp 5, (MLn)-M-2 = Rh(cod) a, Ir(cod) b, Mn(CO)(3) c and FeCp d, respectively. Crystal structures of 3a, 3b and 5c are described showing two different ligand conformations in form of two rotamers. The energetic difference between these both rotamers is insignificant small in the gas phase according to DFT calculations. The rotation barrier for the species has been determined to 23 kJ/mol. According to the absence of intermolecular interactions in the solid state, the preference for one of the conformers is deduced from packing effects. All complexes are investigated by cyclic voltammetry. The shift of the redox potentials with respect to the mononuclear reference systems is a suitable tool to determine intermetallic electronic interaction. For some compounds, the normal behaviour with an increasing separation of the redox potentials is observed. A second group of complexes shows the opposite behaviour with a decreasing in the potential differences. A mechanism of intramolecular catalytic oxidation is supposed for that species.