Enantiodifferentiation of Aliphatic Ethers by the Dirhodium Method

Abstract

The enantiomers of chiral aliphatic ethers can easily bedifferentiated by the dirhodium method, i.e. by 1H and13C NMR spectroscopy in the presence of the chiral auxiliary Rh2[(+)‐MTPA]4. This is the first direct chiral recognitionby spectroscopic methods in this class of ligand compounds. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Enantiodifferentiation of polyethers by the dirhodium method. Part 2: Cyclotriveratrylenes and cryptophanes

“…Thereby, equivalent nuclei give rise to the same signal due to time-averaging. The same phenomenon has been observed for deMeijere's polyethers, 8 , by applying variable-temperature 1 H and 13 C NMR spectroscopy. This experiment, hitherto unreported, proved that there are at least two mechanisms of molecular dynamics: (a) There is a coalescence behaviour of all NMR signals on lowering the temperature indicating an adduct formation as described in Scheme 2; at low temperature, both ligand species, free and complexed, can be observed separately, and a ligand exchange barrier of 44-45 kJ/mol can be estimated.…”

“…Recently, the dirhodium method developed by Duddeck et al 7 appeared as a promising tool to discriminate between the two enantiomers of a series of cyclic ether derivatives such as the compounds prepared by de Meijere et al 8 For instance, the ability of the chiral dirhodium tetracarboxylate complex Rh * (Scheme 1) 9 to differentiate between the two enantiomers of 2,8,12-trioxahexacyclo[8.3.0.0 3,9 .0 4,6 .0 5,13 .0 7,11 ]tridecane and 4,7,11-trioxapentacyclo[6.3.0.0 2,6 .0 3,10 .0 5,9 ]undecane by 1 H and 13 C NMR spectroscopy was demonstrated, with signals being duplicated by up to Dm = 16 Hz. 8 The complexation of a very weak Lewis base such as the ether moieties encountered in this cyclic ether derivative, prompted us to test the dirhodium method with a series of CTV and cryptophane molecules. We selected six chiral CTV 1-6 and four chiral cryptophanes 7-10 for detailed analysis, each having different symmetry and substituents (Scheme 1); two more less symmetric cryptophane analogues, 11 and 12, were studied as well.…”

Origin of 13C complexation shifts in the adduct formation of 2‐butyl phenyl ethers with a dirhodium tetracarboxylate complex

“…[5,18] As tested for 1, other molar ratios, e.g. 2.5 : 1, afford practically the same NMR spectroscopic results.…”

“…Although the ethers are weak ligands in their ability to bind to dirhodium tetracarboxylates, [5,18] some 13 C signal splittings can be observed for C-2 ( ν = 3-6 Hz) and C-2 /6 ( ν = 1-3 Hz) of 1 and 2a-2d due to the formation of diastereomeric adducts with Rh * , respectively. If, however, the substituent is in ortho-position (3a-3d), diastereomeric dispersion effects are significantly weaker if observable at all.…”

Adducts of nitrogenous ligands with rhodium(II) tetracarboxylates and tetraformamidinate: NMR spectroscopy and density functional theory calculations

“…There are two NMR methods based on the ability of dirhodium salts to the formation of axial adducts. The first method makes use of optically pure rhodium(II) tetracarboxylates (usually Mosher's acid salts) as chiral recognition agent and is designed to the determination of optical purity of chiral compounds by NMR methods . The second application allows one to establish the compound configuration ( R or S ) by NMR spectroscopy .…”