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Efficient Resolution of Dinuclear Triple Helicate By Asymmetric Extraction/Precipitation Using TRISPHAT Anions as Resolving Agents

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Published in Chemistry - A European Journal. 2000, vol. 6, no. 23, p. 4297-4304
Abstract Tetradentate 1,2-bis[4-(4´-methyl-2,2´-bipyridyl)]ethane ligand (3) and Fe(NH4)2(SO4)26 H2O combine in a 3:2 ratio to form the racemic helicate [Fe2L3]4+ (4), as reported by Elliott et al. We now show that the enantiomeric purity of 4 can be efficiently measured by 1H NMR by the use of the TRISPHAT (1) salt as a chiral shift reagent. Large differences in chemical shifts (δδ of up to 0.3 ppm, 20 % [D6]DMSO in CD3CN) are observed between the enantiomers of 4 upon addition of [nBu4N][-1]. The resolution of 4 by asymmetric extraction was attempted: addition of an organic solution of [cinchonidinium][δ-1] salt (2 equiv) to an aqueous solution of helicate 4-(SO4)2 led, after vigorous stirring, to the extraction of the homochiral diastereomer [P-4][δ-1]4 into the organic layer along with the precipitation of the heterochiral diastereomer [M-4][δ-1]4 at the interface (diastereomeric ratio>49:1 for both processes). An enantioenriched fraction of [P-4][SO4]2 remained in the aqueous layer. To obtain only two fractions of resolved helicate and develop this procedure into an efficient resolution protocol, four equivalents of [cinchonidinium][δ-1] salt were used as the resolving agent. Chemically and diastereomerically pure [P-4][δ-1]4 and [M-4][δ-1]4 helicate salts were then obtained in excellent yields.
Keywords ChiralityChiral resolutionHelical structuresIronSupramolecular chemistry
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JODRY, Jonathan, LACOUR, Jérôme. Efficient Resolution of Dinuclear Triple Helicate By Asymmetric Extraction/Precipitation Using TRISPHAT Anions as Resolving Agents. In: Chemistry - A European Journal, 2000, vol. 6, n° 23, p. 4297-4304. https://archive-ouverte.unige.ch/unige:7767

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Deposited on : 2010-06-21

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