Separation lanthanide-induced shifts

The LIS (Lanthanide Induced Shift) NMR technique is useful for such analysis25 and the separation of olefin enantiomers such as limonene, a-camphene and /J-pinene has been performed upon addition of silver salts such as Ag(fod) or Ag(hfc) to the commonly used lanthanide chiral salts such as Ln(tfc )3 or Ln(hfc)3, where fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyloctanedione, hfc = heptafluoro-3-butyrylcam-phorato and tfc = trifluoroacetylcamphorato. 

Quantitative separation of the n contact and pseudocontact contributions to the lanthanide induced shifts (LIS) in aniline and m-and p-toluidines has been reported. (395, 396) The contact shift patterns are estimated from the rr-spin density distribution of the appropriate cation radical or from the Ni(acac)2 induced shifts. The separation of the shifts was checked by comparing the relative contact shift contribution with the <5 ) value of Golding and Halton (389) and the remaining pseudocontact contribution with the calculated values of Bleaney s theory. (380)... 

Solution structures may be determined on the basis of lanthanide-induced shifts. This is, however, a difficult task the exact origin of the induced NMR shifts is unknown, a great number of lanthanide complexes have a low symmetry and they often present a high lability, e.g., between conformers. The separation of the various contributions to the NMR shifts may be achieved by several procedures under favourable conditions, or can be avoided by selecting the Yb(III) ion as paramagnetic center, since this ion induces shifts that are essentially dipolar in origin. The dipolar shift is expressed by ... 

The interaction between lanthanide shift reagents containing p-diketones and several methyl 2,3-anhydro-4,6-0-benzylidene-D-hexopyranosides has shown that the carbohydrate may be bound to the reagents in either monodentate or chelated manner. The separation of xylitol and L-arabitol on cation exchange resin in the La form is mentioned in (Chapter 23. The n.m.r. shifts induced by complexation between per-O-methylated aldopyranoses and metal cations (mostly Eu ) have been studied and an order of stability of the complexes has been deduced. Treatment of (dppelPtClj with 2 equiv. of KOSiMej and a slight excess of l,2 5,6-di-0-isopropylidenemannitol has afforded the (dppe) Pt (glycolate) complex. ... 

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