Copper complexes ligand exchange

The most widely used approach for the separation of enantiomers by TLC is based on a ligand exchange mechanism using commercially available reversed-phase plates impregnated with a solution of copper acetate and (2S,4R,2 RS)-4-hydroxy-l-(2-hydroxydodecyl)proline in optimized amounts. Figure 7.9 (10,97,98,107-109). Enantiomers are separated based on the differences in the stability of the diastereomeric complexes formed between the sample, copper, and the proline selector. As a consequence, a prime requirement for separation is that the seumple must be able to form complexes with copper. Such compounds include... 

It has been recognized that sulfur donors aid the stabilization of Cu(i) in aqueous solution (Patterson Holm, 1975). In a substantial study, the Cu(ii)/Cu(i) potentials and self-exchange electron transfer rate constants have been investigated for a number of copper complexes of cyclic poly-thioether ligands (Rorabacher et al., 1983). In all cases, these macrocycles produced the expected stabilization of the Cu(i) ion in aqueous solution. For a range of macrocyclic S4-donor complexes of type... 

Ligand exchange has proved to be very successful in the separation of several enantiomers. Davankov and Rogozhin (41) used chiral copper complexes bonded to silica. The enantiomeric separation is based essentially on the formation of diastereomeric mixed complexes with different thermodynamic stabilities. It is generally accepted that chiral discrimination proceeds via the substitution of one ligand in the coordination sphere of the metal ion. Ligand exchange technique is especially effective for the enantiomeric resolution of aminoacids, aminoacids derivatives, and hydroxy acids (42). 

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