Chiral shift reagents for NMR-spectroscopy. A simple and improved access to lanthanide-tris-chelates of d-3-TFA-camphor
✍ Scribed by V. Schurig
- Publisher
- Elsevier Science
- Year
- 1972
- Tongue
- French
- Weight
- 154 KB
- Volume
- 13
- Category
- Article
- ISSN
- 0040-4039
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✦ Synopsis
The utility of paramagnetic lanthanide-tris-R-diketonates as pseudo-contact shift reagents in NMR-spectroscopy has first been demonstrated by HINCKLEY (1). More recently, chiral lanthanide-tris-d-3-acyl-camphorates have been applied to the direct determination of enantiomeric compositions (optical purity of enantiomeric substrates) (2-S) Europium-tris-d-3-trifluoroacetyl-camphorate ( Eu(TFA-Cam)3 ) has been found to be a most efficient chiral shift reagent (3,5)_ This compound is synthesized (5'6) from d-3-TFA-camphor (which is purified only with difficulty) and europium(II1) nitrate hydrate in the presence of a base accordihg to the general procedure of EISENTRAUT and SIE-VERS ('**) . However, these shift reagents are much more easily obtained by the quantitative homogeneous exchange reaction of lanthanide nitrates (8) with the barium salt of d-3-TFA-camphor ( 8a(TFA-Cam)2 ) ('I in ethanol, e.g.: 2 Ln(N03)3. n H20 + 3 Da(TFA-Cam)2 = ( Ln = trivalent lanthanum series ion)
The barium chelate ( 9) is prepared