Synthesis of novel chiral bis(ferrocenyl) ligands and their use as voltammetric metal cation sensors

Bis(ferrocenyl) derivatives 3a, 3c and 3d containing secondary chelating substituents act as efficient voltammetric sensors of Mg2+ and Zn2+ ions in acetonitrile solution in concentrations as low as 10 mol%: a new redox peak appears in the cyclic voltammogram, positively shifted by 170–225 mV for 3a, 160–175 mV for 3c and 160–170 mV for 3d. Compounds 3b and 4 are selective for Zn2+ (215 mV shift) and Mg2+ (205 mV shift) ions, respectively, whilst 3d is also responsive to Ca2+ ions (165 mV shift) with no interference from a large excess of several other metal salts. The X-ray crystal structure of 3a is also reported.