Coordination of Ferrocenyl Ligands Bearing bipy Subunits: Electrochemical, Structural and Spectroscopic Studies

Abstract

The coordinative properties of mono(bipy) and bis(bipy) (bipy refers to 6- or 6,6′-substituted 2,2′-bipyridine) carbonyloxy- and carboxamido-bridged derivatives of ferrocene L1−5 towards a number of metal cations (CuI, CuII, NiII, FeII, CoII, HgII, PbII, AgI) have been investigated by the interplay of voltammetry, mass spectrometry and X-ray diffraction studies. Particular attention was paid to the electrochemical recognition properties of these redox-active ligands, as monitored by modulation of the ferrocene/ferricinium redox couple upon complexation. It was found that the bis(bipy)-bridged ligands exhibit a sandwich effect that gives rise to a well-behaved voltammetric wave for the ferrocene fragment as an elegant signature of complexation. The ferrocenyl ester-bridged bis(bipy) ligand L2 forms a 2:2 complex in the solid state with CuI, while the crystal structure of the CuII complex reveals 1:1 stoichiometry. Upon dissolution, the 2:2 species dissociate rapidly into the [CuL2]+ complex. Finally, electrochemical and FAB-MS data have been used to conclude that these ferrocenyl ligands bind to iron(II) to generate unusual [Fe(bipy)2]2+-type complexes. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)