Chiral paramagnetic shift reagents

With Paramagnetic Chiral Lanthanide Shift Reagents... 

NMR spectroscopy the NMR spectrum of the sample in the presence of a chiral solvating agent (see Section 3.1.4.1.) or a chiral paramagnetic lanthanide shift reagent (see Section 3.1.4.2.2.) is recorded. The determination of enantiomeric purity rests on the nonequivalence of externally enantiotopic nuclei which are rendered externally diastereotopic in a non-racemic chiral environment. 

In the case of the direct method , NMR spectra of enantiomers are recorded in the presence of a nonracemic chiral solvating agent (CSA, Pirkle s method)78, or after addition of a paramagnetic chiral (nonracemic) lanthanide shift reagent (LSK) to the solution of the sample. 

The development of achiral lanthanide shift reagents preceded that of chiral LSRs. It was demonstrated86 in 1969 that paramagnetic Eu(thd)3 and Eu(fod)3 (Tablet), as well as the... 

CSR (Chiral shift reagent) A paramagnetic lanthanide complex of known enantiomeric purity used to induce anisochrony in enantiomers of a racemate for NMR analysis. See Section 2.3.3. 

Bimetallic complexes formed using a lanthanide tris (3-diketonate and silver 3-diketonate are useful shift reagents for soft Lewis bases such as alkenes, aromatics, phosphines, and halogenated compounds.Chiral lanthanide tris (3-diketonates of tfc and hfc are used in forming the binuclear reagents. A variety of silver 3-diketonates have been evaluated, but only the silver chelate of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione [Ag (fod)] is commercially available. The mixture forms a tetrakis chelate anion to which the silver is ion paired ([Ln (P-dik)4 ]Ag" "). In the bimetallic reagent, the silver binds to the soft Lewis base while the paramagnetic lanthanide ion causes perturbations in the chemical shifts that account for the enantiomeric discrimination. 

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