Synthesis and electrochemistry of novel heteronuclear Fe–Ru bi- and quatermetallocenes, conjugatively connected by ethene and thiophene bridges

Abstract

( E)-2-(1′-Formylruthenocenyl)ethenyl-1′,2,2′,3,3′,4,4′,5-octamethylferrocene ( 1) and (all- E)-2,5-bis[2-[1′-[2-(1′,2,2′,3,3′,4,4′,5-octamethylferrocenyl)ethenyl]ruthenocenyl]ethenyl]thiophene ( 2) were synthesized by a sequence of Wittig olefinations. The X-ray structure of 1 is reported. The cyclic voltammogram of compound 1 shows the irreversible one-electron transfer expected for ruthenocene and a reversible wave for the octamethylferrocene moiety. Both waves occur at about the same potential as observed for the parent metallocenes. Compound 2, however, exhibits completely unusual redox properties. In contrast to most ruthenocene-containing compounds, a reversible two-electron transfer is observed at a significantly lower potential than found usually for ruthenocenes that can be attributed unambiguously to the independent oxidation/reduction of the two ruthenocene moieties. The unexpected stability of the oxidation products must be due to the presence of the thiophene–ethene bridge, which facilitates the oxidation reaction and stabilizes the reaction products by delocalization of the valence electrons.