Leibniz University Hannover, Institute of Organic Chemistry, Schneiderberg 1B, D-30167, Hannover, Germany.
Org Biomol Chem. 2011 Oct 7;9(19):6542-50. doi: 10.1039/c1ob05665d. Epub 2011 Aug 2.
Thirteen enantiopure paddlewheel-shaped dirhodium(II) tetrakiscarboxylate complexes have been checked for their efficiency in the dirhodium method (differentiation of enantiomers by NMR spectroscopy); six of them are new. Their diastereomeric dispersion effects were studied and compared via so-called key numbers KN. Adducts of each complex were tested with five different test ligands representing all relevant donor properties from strong (phosphane) to very weak (ether). Only one of them, the dirhodium complex with four axial (S)-N-2,3-naphthalenedicarboxyl-tert-leucinate groups (N23tL), showed results significantly better for all ligands than the conventional complex Rh* [Rh(II)(2)(R)-(+)-MTPA; MTPA = methoxytrifluoromethylphenylacetate]. On the basis of (1)H{(1)H} NOE spectroscopy and X-ray diffraction, a combination of favourable anisotropic group orientation and conformational flexibility is held responsible for the high efficiency of N23tL in enantiodifferentiation. Both complexes, Rh* and N23tL, are recommended as chiral auxiliaries for the dirhodium experiment.
13 种对映纯桨轮型二钌（II）四羧酸盐配合物已被检查其在二钌方法（通过 NMR 光谱对映体进行区分）中的效率；其中有 6 种是新的。通过所谓的关键数 KN 研究并比较了它们的非对映体分散效应。每种配合物的加合物都用 5 种不同的测试配体进行了测试，这些配体代表了从强（膦）到非常弱（醚）的所有相关供体性质。只有一个，即具有四个轴向（S）-N-2,3-萘二甲酸叔丁酯基-亮氨酸（N23tL）基团的二钌配合物，与传统的 Rh* [Rh（II）（2）[（R）-（+）-MTPA]（4）；MTPA = 甲氧三氟甲基苯乙酸酯]相比，对所有配体的结果都明显更好。基于（1）H{（1）H} NOE 光谱和 X 射线衍射，认为有利的各向异性基团取向和构象灵活性的组合是 N23tL 在对映体分化中具有高效率的原因。建议将 Rh*和 N23tL 这两种配合物作为二钌实验的手性助剂。
