Novel chiral N4S2- and N6S3-donor macrocyclic ligands: synthesis, protonation constants, metal-ion binding and asymmetric catalysis in the Henry reaction

Abstract

New hydrophobic chiral macrocyclic ligands L1–L3 with chiral diamino and thiophene moieties have been synthesized by the Schiff base condensation approach. Protonation constants of L1 and L2 were determined by potentiometry titration. Metal-ion binding experiments exhibited that L1 and L3 are pronounced in selective recognition, Ag⁺, Cu²⁺ and Ca²⁺ ions among the surveyed metal ions (Cu²⁺, Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Pb²⁺, Ag⁺, Li⁺, Na⁺, K⁺, and Ca²⁺). L1 was found to spectroscopically detect the presence of Cu²⁺ and Ca²⁺ to function as a multiple readout sensor. The detection limit for Ca²⁺ ions was found to be 9.8 × 10⁻⁵ M in CH₂Cl₂–MeOH solution. The trimeric chiral ligand L3 has been shown to be an efficient auxiliary in a Zn(II)-mediated enantioselective Henry reaction.