Lanthanide nmr shift reagents. A powerful new stereochemical tool

Abstract

Lanthanide NMR Shift Reagents A powerful new stereochemical tool Tlie effects of paramagnetism on nuclear magnetic resonances have been studied since the very beginning of nuclear magnetic resonance (nmr) spectroscopy (/). It has been only within the last few years, however, that paramagnetic effects have been systematically applied to structure determination and peak assignments for organic molecules. Most of the work to date has been done with various lanthanide complexes (2-8) which produce spectral simplifications in the nmr spectra of aldehydes, ketones, alcohols, amines, and other molecules having a relatively basic lone pair of electrons (9a). The addition of certain lanthanide complexes ("Shift Reagents") to an nmr solu-

Rare-earth beta-diketonates

“…The synthesis of complexes of perfluoroacetylacetone (heptafluoroacetylacetone, Hacac-F 7 ) turned out to be a difficult task (Petrov et al, 2002). Reaction of freshly precipitated Eu(OH) 3 •nH 2 O led to the formation of europium(III) trifluoroacetate, rather than to the formation of a β-diketonate complex.…”

“…In the 1970's and 1980's several review papers devoted to lanthanide NMR shift reagents have been published (Campbell, 1971;von Ammon and Fischer, 1972;Becker, 1972;Peterson and Wahl, 1972;Horrocks, 1973;Slonim and Bulai, 1973;Cockerill et al, 1973;Williams, 1974;Voronov, 1974;Reuben, 1975aReuben, , 1975bFlockhart, 1976;Sullivan, 1978;Reuben and Elgavish, 1979;Inagaki and Miyazawa, 1981;Forsberg, 1981). A very comprehensive overview of the use of tris(β-diketonato)lanthanide complexes as NMR shift reagents can be found in the book of Wenzel (1987).…”

Total Synthesis via Biomimetic Late-Stage Heterocyclization: Assignment of the Relative Configuration and Biological Evaluation of the Nitraria Alkaloid (±)-Nitrabirine

“…Complexes of europium and praseodymium are by far the best shift reagents in this respect, giving shift broadenings of only 0.003 and 0.005 Hz per hertz of shift, respectively. 26 The principle is based on chelate-like interactions between the europium and the lone-pair electrons of the oxygen of the hydroxyl group and the sp 2 nitrogen of the imidazole ring of 5 on one hand and its epimer 5′ on the other hand. The chemical shift difference increases with the increasing concentration of shift reagent and the stability of the complexes.…”

Total Synthesis via Biomimetic Late-stage Heterocyclization, Assignment of the Relative Configuration and Biological Evalu-ation of the Nitraria Alkaloid (±)-Nitrabirine

“…Complexes of europium and praseodymium are by far the best shift reagents in this respect giving shift broadenings of only 0.003 and 0.005 Hz/Hz of shift, respectively. 24…”