Alkali-metal binding properties of simple ferrocenyl- and ruthenocenyl-substituted aza-crown ethers

Reaction of 1-chlorocarbonyl-ferrocene or -ruthenocene with aza-15-crown-5 (1,4,7,10-tetraoxa-13-azacyclopentadecane) afforded the respective amide-linked metallocene crowns. Nucleophilic displacement of trimethylamine from trimethylammoniomethyl-ferrocene or -ruthenocene iodides with aza-15-crown-5 yielded the corresponding methylene-linked crowns. Variable-temperature 13C NMR investigation of the hindered rotation about the amide links of the amide-linked crowns in the presence of guest cations indicated that cation complexation occurs exclusively within the crown ring. Extraction experiments with a range of metal-cation dye salts revealed a favourable binding capacity for the methylene-linked crowns. Detailed 13C NMR analysis of sodium and potassium ion binding by these systems suggests the presence of a stabilising interaction between the metallocene π system and the crown-bound cation. Cyclic voltammetric analysis of metal-ion binding by the amine-linked crowns revealed cation-induced shifts of the appropriate redox couple comparable with those reported for related systems.