Determination of enantiomeric purity using chiral lanthanide shift reagents

Abstract

Chiral tris[/3-diketonato]europium(III) chelates 1-14 have been synthesized and tested for their effectiveness in inducing chemical shifts ( ) between corresponding resonances of enantiomeric organic substances.Judged by the dual criteria of generality of application as reagents for determining enantiomeric composition and ease of preparation, the most useful of these chiral shift reagents are tris[d,i/-dicampholylmethanato]europium(III)(1, Eu(dcm)3), tris[3-trifluoroacetyl-i/-nopinonato]europium(III) (9), and tris[3-trifluoroacetyW-camphorato]europium(III) (10). Compound 1, Eu(dcm)3, is the most effective reagent for the resolution of enantiotopic resonances; reagents 9 and 10 are considerably less effective, but are more easily prepared. It is not presently possible to predict in any detail the influence of a particular chiral shift reagent on a mixture of enantiomers, and achieving useful resolution between the signals of enantiotopic protons in complex, polyfunctional structures may require testing several chiral shift reagents, and varying sample concentrations and temperature. Chiral shift reagents are applicable in principle to the determination of enantiomeric composition of most "hard" organic bases; they are not effective with most "soft" bases, with acids, or with certain chelating agents. Conditions for use of these

Cyclopentadienyl platinum(IV) complexes: 1H, 13C nuclear magnetic resonance and optically active shift reagent study

“…The splitting of the peaks is due to the diastereotopic interaction of the two enantiomers of 5 with the chiral shift reagent (28,29). Two reasons are generally invoked to explain this splitting: one is geometry, the other, differing equilibrium constants for the complexes formed.…”

“…Differences in equilibrium constants have also been postulated as a reason for the splitting and resolution of the spectra of chiral molecules (28,29). The diastereomeric complexes formed between 5 and Eu-Opt might well have different equilibrium constants and this would cause different shifts and hence splitting of peaks.…”

Signal separation and determination of the enantiomeric purity of primary amines with (−)-myrtenal – a 13C NMR study

“…by introduction of aromatic group and/or one or more fluorine moeities. The new compounds could be more advantageous than 1R -((/)-myrtenal to obtain greater Dd and could allow the use of other NMR sensitive nuclei as 19 F.…”

NMR-based Enantiodifferentiation of Chiral trans-2-Phenylcyclopropane Derivatives Using a Chiral Lanthanide Shift Reagent

“…Care is required in determining absolute configurations based on empirical correlations of chemical shifts in the presence of chiral shift reagents. While several studies have determined absolute configurations based on ΔΔδ, [11][12][13][14][15][16][17][18][19] there are cases in which the sign of ΔΔδ changes within the same series of compounds. 20,21 In the current study, absolute configurations are considered accurate because the differences in the patterns of R and S enantiomeric methyl chemical shifts (ΔΔδ) were the same (i.e., the downfield chemical shift of the S enantiomer matches the upfield chemical shift of the R enantiomer).…”