Europium tris

For the determination of the enantiomeric excess. 23 mg of the mi-hydroxy ester (containing 2 5% //-product) and 9 mg of tris[3-(heptafluoropropylhydroxymethylene)-a-camphorato]europium are dissolved in 0.5 mL of CDC13. The ec is calculated from the peak heights and areas of the resolved doublets, due to the methyl groups attached to C-2. of the minor (f) 1.74) and major (<5 1.98) enantiomers. 

Europium, tris(2,2,6,6-tetramethyl-3,5-heptanedione-quinuclidine)-stereochemistry, 1, 81 Europium complexes... 

The enantiomeric purity of optically active sulphoxides can be determined by chiral lanthanide shift reagents such as tris(3-trifluoroacetyl-ti-camphorato)europium(III) and tris(heptafluorobutyryl-d-camphorato)europium(III)218-219-221, the latter shown in Scheme 23. 

A 100 MHz. proton magnetic resonance spectrum (chloroform d) of the amine in the presence of an equal amount of the chiral shift reagent, tris[3-(trifluoromethylhydroxymethylene)-d-camphorato]euro-pium(III)4 (submitters), or in the presence of an equal amount of tris[3-(heptafluoropropylhydroxymethylene)-d-camphorato]europium-(III) (checkers), revealed that the product contained no detectable enantiomeric isomer. 

The submitters report obtaining the product in 99% yield. The enantiomeric excess of the Mosher ester of 3 was measured to be 98% using a Chiralcel OD column (40% 2-propanol/hexane). This optical purity measurement substantiated the optical purity assessment made by 111 NMR studies of 3 and racemic 3 prepared using a different method3. Addition of the chiral shift reagent tris[3-(heptafluoropropylhydroxymethylene)-(+)-camphorato]europium (III) resulted in clear resolution of the respective aromatic proton signals for the two enantiomers, which was demonstrated with the racemate. Under similar conditions, NMR analysis of 3 showed that within the detectable limits of the experiment (ca. <3%), there was none of the disfavored enantiomer. 

The relative amounts of sodium alkenesulfonate isomers and sodium hydroxyalkanesulfonate isomers have been determined with 1.19-2.07% precision by NMR measurements of the methyl signals of methyl esters in carbon tetrachloromethane with 1.3 mol equivalent tris(heptafluorobutanoylvivaloyl-methanato)europium(I) and tri(dipaloylmethanato)europium as shift reagent. The... 

A closely related method does not require conversion of enantiomers to diastereomers but relies on the fact that (in principle, at least) enantiomers have different NMR spectra in a chiral solvent, or when mixed with a chiral molecule (in which case transient diastereomeric species may form). In such cases, the peaks may be separated enough to permit the proportions of enantiomers to be determined from their intensities. Another variation, which gives better results in many cases, is to use an achiral solvent but with the addition of a chiral lanthanide shift reagent such as tris[3-trifiuoroacetyl-Lanthanide shift reagents have the property of spreading NMR peaks of compounds with which they can form coordination compounds, for examples, alcohols, carbonyl compounds, amines, and so on. Chiral lanthanide shift reagents shift the peaks of the two enantiomers of many such compounds to different extents. 

Nitrone 1,3-DC reactions are still the most general approach to isoxazolidines. The stereocontrol is usually achieved by the use of chiral nitrones and/or dipolarophiles, but new interesting achievements on Lewis acid catalyzed cycloadditions are also frequently reported. Tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanatedionate) europium(III) [Eu(fod)3] selectively activated the Z-isomer of C-alkoxycarbonyl nitrone 75 existing as an E,Z-equilibrium mixture by forming the (Z)-75-Eu(fod)3 complex. (Z)-75-Eu(fod)3 reacted with electron-rich dipolarophiles such as vinyl ethers to give the trans-adducts with excellent diastereoselectivity <06T12227>. 

Preparation.—Two new synthetic routes to simple iodo-phosphines have appeared this year. Thus phosphorus tri-iodide (8) is produced in fairly good yield when the iodides of lanthanum, strontium, or europium are treated with the corresponding phosphates.14 Tetraiododiphosphine (9) is formed in 75—80% yield, by the reaction... 

FIGURE 5. Proton NMR spectra of solutions prepared from (S)-a-phenylethylamine [(S)-22] (10 pL) (upper spectrum) and a mixture of (R)- and (S)-a-phenylethylamine (R)- and (S)-22] (7 and 5 J-L, respectively) (lower spectrum) in 0.3 mL of a carbon tetrachloride solution of tris[3-(ferf-butylhydroxymethylene)-(i-camphorato]europium(III) (96). The chemical shift scale applies only to the lower spectrum. Reprinted with permission from Reference 82. Copyright (1970) American Chemical Society... 

Eu(dcm), tris(d, 4-dicampholylmethanato (europium (III) Eu(tfc)3, tris(3-trifluoroacetyW-camphorato)europium (III). 

The first report of a cycloaddition reaction in the presence of an optically active catalyst13 appeared in 198314a. The dienes 14 add to benzaldehyde in the presence of 1 mol% of the chiral lanthanide NMR shift reagent Eu (hfc)3, i.e. tris[3-(heptafluoropropyl-hydroxymethylene)-(+)-camphorato]-europium(III), to give, after treatment with trifluo-roacetic acid, the dihydro-y-pyrone 15 enriched in the (R)-enantiomer, the degree of... 

Similar differentiation between enantiomers by means of NMR can also be achieved by the use of chiral lanthanide shift reagents (243). Tris-[3-(heptafluoropropylhydroxymethylene)-d-camphorato] -europium was used for the first time (244) for determining the enantiomeric content of benzyl methyl sulfoxide 34. The enantiomeric composition of the partially resolved methyl p-tolyl sulfoxide 41 was estimated using tris-[3-(r-butylhydroxymethylene)-c -camphorato]-europium (245). Another complex of europium, tris-[3-(trifluoro-methylhydroxymethylene)-c -camphorato] europium (TFMC), in contrast to those mentioned above, was effective in the differentiation of various enantiomeric mixtures of chiral sulfinates (107), thiosul-finates (35), and sulfinamides (246). 

The use of chiral shift reagents, e.g. tris-[3-(trifluoromethyl)- or -(hepta-fluoropropyl)-hydroxymethylene)-d-camphorato)]europium, praseodymium, or ytterbium, in the determination of optical purities of chiral alcohols, ketones, esters, epoxides, amines, or sulphoxides, or in the separation of n.m.r. signals of internally enantiotopic protons e.g. PhCHjOH), has been described. 

Other techniques, such as C.D. spectral change, have been used to demonstrate the presence of octa coordination for lanthanide ion in a system containing Eu(FOD)3 and alcohols or ketones (28). However, the anionic tetrakis complexes e.g. Eu(acac)i, Eu(benzac)i, Eu(DBM)i, Eu(BTFA)4, tend to dissociate into the tris-complex and L in alcoholic solution. The degree of dissociation depends on the complex as well as the polarity of the medium. In alcohol-DMF medium the dissociation is enhanced compared to the alcoholic solutions (29). The end product of these dissociation reaction may well be an octacoordinated species. Fluorescence emission from the coordinated europium ion was also helpful in estabhshing the nature of the species in solution 29). 

These considerations are probably also of value in the study of Eu + luminescence in chelates. Napier et al. 80) have recently demonstrated the importance of the Eu3+ c.t. state for the absence of Eu3+ emission in tris (acetylacetonate) europium(III). 

The very useful lanthanide shift reagents, which facilitate analysis of molecular stereochemistry because of their line-broadening characteristics in NMR spectra, were studied when bound as a chelate complex to thietanes. X-Ray analysis of the adduct 3,3-dimethylthietane 1-oxide with tris(dipivalo-methanato)europium(III) [Eu(dpm)3] revealed the structure of a seven-coordinate complex (271). ... 

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