Use of chiral lanthanide shift reagents in the elucidation of NMR signals from enantiomeric mixtures of polycyclic compounds †

Application of a 1H δ‐resolved 2D NMR experiment to the visualization of enantiomers in chiral environment, using sample spatial encoding and selective echoes

“…4(b)). We note here that a further optimized amount of the lanthanide shift reagent, or even the use of a mixture of chiral shift reagents [16] would yield a 'nicer' elucidation of the desired NMR signals. However, in this series of experiments we are interested in studying the ability of the 2D pulse sequence to elucidate even small variations between two enantiomers whatever the quality of the chiral discrimination process.…”

“…[12] In the case of enantiomers dissolved in an isotropic solvent with a chiral shift reagent, the intermolecular interaction is diastereoisomeric and the shift is thus different for each enantiomer. [1,16] Since the interaction with the shift reagent often leads to a fast equilibrium between a free and a coordinated form for both enantiomers, the measured shifts correspond to the average between the compound near and far from the paramagnetic center. Its value depends therefore on the relative solute/shift reagent concentration.…”

“…3(a)) when using a europium (III) compound as a chiral shift reagent. [16] In a 5 mm NMR tube, 37 mg of (±)2-methyl-isoborneol were dissolved in 651 mg of CDCl 3 . The corresponding 1 H spectrum is shown in Fig.…”

NMR determination of enantiomeric composition of 1-substituted 3-amino-1,2-dicarba-closo-dodecaboranes using Eu(hfc)3

“…Commercially available lanthanide chelates, i.e., europium(III) tris [3-(trifluoromethylhydroxymethylene)camphorate] and europium (III) tris [3-(heptafluoropropylhydroxymethylene)-(+)-camphorate], Eu(tfc) 3 and Eu(hfc) 3 are most frequently used as such reagents. It has been reported in literature that in many cases Eu(hfc) 3 is more effective CSR than Eu(tfc) 3 , ensuring greater differentiation of the enantiomers resonances [2]. However, this methodology has not been previously applied for carborane derivatives with asymmetry resulting from relative position of substituents in the carborane cage ( Fig.…”

“…Recently we turned our attention to the preparation of enantiomers of 1-R-3-NH 2 -1,2-closo-C 2 B 10 H 9 , R = Me (1), Ph (2), and i-Pr (3) [4], so needing a good analytical method for determination of enantiomeric excess. For this purpose a systematic study of determining the enantiomeric composition of 3-aminocarboranes 1-3 by NMR spectroscopy using Eu(hfc) 3 as a chiral shift reagent has been undertaken.…”