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

摘要

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 degrees C. The electrochemical Fe-II/Fe-III potential 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 [D-6]dimethyl sulfoxide ([D-6]DMSO), the ion pairs are separated.