Wenzel Thomas J, Wenzel Bradford T
Department of Chemistry, Bates College, Lewiston, Maine 04240, USA.
Chirality. 2009 Jan;21(1):6-10. doi: 10.1002/chir.20570.
Diamagnetic lanthanium(III) and lutetium(III) tris beta-diketonate complexes of 3-(trifluoroacetyl)-d-camphor, 3-(heptafluorobutyryl)-d-camphor, and d,d-dicampholylmethane are shown to be effective chiral NMR shift reagents for determining the enantiomeric purity of compounds with hard Lewis base functional groups. These include substrates with amine, alcohol, epoxide, sulfoxide, and oxaxolidine moieties. Enantiomeric discrimination is observed in the (1)H NMR spectrum. Diamagnetic lanthanide complexes represent an alternative to paramagnetic varieties that often cause too much line broadening in the NMR spectra. The choice of which metal to use varies with substrate. Similarly, there is no consistent trend with ligand as not one of the complexes is consistently better than the others for all substrates. The enantiomeric discrimination also varies with solvent. Comparisons show that the chiral recognition was usually larger in benzene-d(6) than in chloroform-d or cyclohexane-d(12).
3-(三氟乙酰基)-d-樟脑、3-(七氟丁酰基)-d-樟脑和d,d-二樟脑基甲烷的抗磁性镧(III)和镥(III)三β-二酮配合物被证明是有效的手性NMR位移试剂，可用于测定具有硬路易斯碱官能团的化合物的对映体纯度。这些化合物包括含有胺、醇、环氧化物、亚砜和恶唑烷部分的底物。在(1)H NMR谱中观察到对映体识别。抗磁性镧系配合物是顺磁性变体的一种替代物，顺磁性变体在NMR谱中常常导致过多的谱线展宽。使用哪种金属的选择因底物而异。同样，配体也没有一致的趋势，因为没有一种配合物对所有底物都始终比其他配合物更好。对映体识别也随溶剂而变化。比较表明，在苯-d(6)中手性识别通常比在氯仿-d或环己烷-d(12)中更大。
