Chiral metal complexes separation

Complexation with Chiral Metal Complexes. This idea was first suggested by Feibush et al.44 The separation is realized by the dynamic formation of diastereomeric complexes between gaseous chiral molecules and the chiral stationary phase in the coordination sphere of metal complexes. A few typical examples of metal complexes used in chiral stationary phase chromatography are presented in Figure 1-13.45... 

Many chiral compounds can be used as selectors, for example, chiral metal complexes, native and modified cyclodextrins, crown ethers, macrocyclic antibiotics, noncyclic oligosaccharides, and polysaccharides all have been shown to be useful for efficient separation of different types of compounds. 

When a chiral metal complex forms a complex with a prochiral alkene , either because it contains a chiral ligand or a chiral metal centre, the resulting complex is a diastereomer. Thus, a mixture of diastereomers can form when the chiral complex coordinates to both faces of the alkene. As usual, these diastereomers have different properties and can be separated. Or, more interestingly, in the catalytic reactions below, the two diastereomers are formed in different amounts and their reactivities are different as well. 

Three reviews of chiral molecules have appeared.52,53,26 The first of these discusses using 7r contacts from supported metal complexes to separate enantiomers by GC and HPLC.52 The second is useful to those reading Portugese.53 The third addresses changing the transport phase affinity of chiral enantiomers by adding chiral additives such as cyclodextrin or a chiral metal complex that form second-sphere contacts in the mobile phase.26... 

The above chemical separations work on the basis of forming diastereomeric pairs as intermediates the same principle applies to the column chromatography techniques that have been developed over the past few years, in which a chiral metal complex is attached to the stationary phase. A number of complexes based on Cu", Ni", Zn" and Co " have been shown to be capable of resolving amino acids. A reverse-phase technique has also been described in which Cu" or Zn" peptide complexes are used in the mobile rather than the stationary phase. ... 

Optically active polymers play a very important role in our modem society. The specialities of optically active polymers are known with their various characteristics as occurred naturally in mimicry. The present review describes the monomers and synthesis of optically active polymers from its helicity, internal compounds nature, dendronization, copolymerization, side chromophoric groups, chiral, metal complex and stereo-specific behaviour. The various properties like nonlinear optical properties of azo-polymers, thermal analysis, chiroptical properties, vapochromic behaviour, absorption and emission properties, thermosensitivity, chiral separation, fabrication and photochromic property are explained in detail. This review is expected to be interesting and useful to the researchers and industry personnel who are actively engaged in research on optically active polymers for versatile applications. 

In general the metal complexes are charged. It is thus possible to convert the racemic mixture of such a complex into a pair of diastereoisomeric species with different physico-chemical properties, in particular solubihty, by association with an enantiomerically pure chiral coimterion [19]. Examples of frequently used such ions are shown in Fig. 3. Then the separation can be achieved by ... 

Chiral ligand-exchange chromatography (CLEC) ° separates enantiomers by the formation of diastereomeric metal complexes. In a first instance the technique was mainly used for the separation of amino acids. Impressive results of the first separations gave rise to intensive investigation in the field and numerous publications appeared in the literature, which have been reviewed. 

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