Double-stranded dimetallic helicates: assembling–disassembling driven by the CuI/CuII redox change and the principle of homochiral recognition

Abstract

In the presence of d¹⁰ metal ions, prone to tetrahedral coordination, ligands containing two bidentate subunits will give rise to double-stranded helical complexes (helicates). Upon electrochemical oxidation of Cu^I to Cu^II, the helicate complex tends to disassemble, thus giving rise to two mononuclear Cu^II complexes with tetragonal geometry. Upon subsequent Cu^II-to-Cu^I electrochemical reduction, two Cu^I complexes instantaneously re-assemble to give the helicate complex. A helicand containing a chiral subunit (e.g. 1,2-substituted cyclohexanediamine) contains a racemic mixture of the R,R and S,S enantiomers. The racemic helicand, reacting with Cu^I, forms dimetallic helicates, in which the two strands show the same chirality, whether R,R or S,S, thus obeying the principle of homochiral recognition.