Synthesis and Electrochemical Investigations of [Ru(eta(5)-Ferrocenyl-Thiophene)(eta(5)-C5R5)](+) Sandwich Compounds

The synthesis of [Ru(eta(5)-2-Fc-3-R-3-4-R-2-5-R-1-A (c) C4S)(eta(5)-C5R5)](+)[PF6](-) (R = H, Me; R-1-R-3 = H; R-1 = Me, R-2 = R-3 = H; R-1-R-3 = Me; R-1 = Fc, R-2 = R-3 = OCH2CH2O; Fc = Fe(eta(5)-C5H4)(eta(5)-C5H5)) is reported with the aim of a better understanding of the influence of pi-thiophene-bonded transition metal units on the thermodynamic stabilities and charge transfer interactions of the resulting compounds and their oxidized intermediates. Within the electrochemical studies, reversible one-electron Fe-based redox events were found for the mono-Fc Ru species, whereby the Fc/Fc(+) redox potential increases as the degree of methylation of the thiophene and the Ru-cyclopentadienyl moiety decreases. For [Ru(eta(5)-2,5-Fc(2)-A (c) C4H2S)(eta(5)-C5R5)](+)[PF6](-) a hindered 2(nd) Fc-based electrode reaction was observed under "weak-coordinating" conditions. Two separated Fc/Fc(+) redox events were detected by the use of stronger solvating solvents or (smaller) anions. With regard to the non complexed 2,5-Fc(2) thiophenes, the thermodynamic stabilities of the appropriate mixed-valent species decrease, when the thiophene is eta(5)-coordinated to [Ru(eta(5)-C5R5)](+). Contrary to the redox potential, the substitution of the [Ru(eta(5)-C5R5)](+) moiety does not have a major impact on the thermodynamic stabilities of the mixed-valent species. The related decrease of electronic coupling between the Fc unit(s) via the thiophene in the corresponding oxidized states, could be verified during UV/Vis/NIR spectroelectrochemical studies.