Chiral and Redox-Active Room-Temperature Ionic Liquids Based on Ferrocene and l-Proline

Article abstract of DOI:10.1002/ejic.201600585

The syntheses of room-temperature ionic liquids (RTILs) combining the naturally occurring amino acid l-proline and ferrocene (Fc) building blocks are reported. After quaternization of ({[(2S)-N-methylpyrrolidine-2-yl]methyleneoxy}carbonyl)ferrocene (1) with alkyl iodides and anion exchange, the resulting diastereomeric (1S,2S)- and (1R,2S)-[(ferrocenylcarbonyl)oxy]methylene-N,N-dialkylpyrrolidine-1-ium RTILs are redox-active and air- and water-stable. They are also thermally stable up to 263 °C. The electrochemical Fe^II/Fe^IIIpotential is shifted to +0.28 V versus Fc/Fc⁺. Before anion exchange, several iodide derivatives were obtained as crystalline products, and their crystal structures are reported. According to the NMR spectroscopic data cation–anion aggregates are present in the non-coordinating solvent CDCl₃. In contrast, in the polar solvent [D₆]dimethyl sulfoxide ([D₆]DMSO), the ion pairs are separated.