Octamethyl‐1, 1′‐di(2‐pyridyl)ferrocene: A Redox‐Active Ligand with a Pronounced Selectivity for Divalent Metal Ions

Octamethyl‐1, 1′‐di(2‐pyridyl)ferrocene ( 1 ) acts as molecular electrochemical sensor for magnesium, calcium, zinc, and cadmium ions in acetonitrile solution. The new redox peak, anodically shifted by ca. 0.40 V, which appears in the cyclic voltammogram of 1 in the presence of even small amounts (10 mol %) of these ions, is unaffected by an excess of alkali metal ions. Metal complexation is accompanied by a batho‐ and hyper‐chromic shift of the band in the visible region of the UV‐Vis spectrum of 1 . A detailed study of the behaviour of 1 towards zinc chloride in acetonitrile solution has revealed that 1 is able to accommodate a maximum of two zinc ions. Oxidation of zinc‐coordinated 1 leads to partial decomplexation. The N‐methyl and N‐benzyl species 1 Me⁺, 1 Me₂²⁺, 1 Bzl⁺ and 1 Bzl₂²⁺ have been synthesized and the former two structurally investigated by X‐ray diffraction. Alkylation causes an anodic shift of the redox potential of the ferrocene nucleus, which is linearly dependent on the number of alkyl groups introduced. Octamethyl‐1, 1′‐di(2‐thiophenyl)ferrocene ( 2 ) has also been synthesized and structurally characterized by X‐ray diffraction. Cyclic voltammetry has revealed that, in contrast to 1 , 2 does not respond to the divalent metal ions studied.