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Efficient Resolution of a Dinuclear Triple Helicate by Asymmetric Extraction/Precipitation with TRISPHAT Anions as Resolving Agents
Author(s) -
Jodry Jonathan J.,
Lacour Jérôme
Publication year - 2000
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20001201)6:23<4297::aid-chem4297>3.0.co;2-#
Subject(s) - extraction (chemistry) , resolution (logic) , precipitation , chemistry , combinatorial chemistry , stereochemistry , materials science , computer science , chromatography , physics , artificial intelligence , meteorology
Tetradentate 1,2‐bis[4‐(4′‐methyl‐2,2′‐bipyridyl)]ethane ligand ( 3 ) and Fe(NH 4 ) 2 (SO 4 ) 2 ⋅6 H 2 O combine in a 3:2 ratio to form the racemic helicate [Fe 2 L 3 ] 4+ ( 4 ), as reported by Elliott et al. We now show that the enantiomeric purity of 4 can be efficiently measured by 1 H NMR by the use of the TRISPHAT ( 1 ) salt as a chiral shift reagent. Large differences in chemical shifts (ΔΔ δ of up to 0.3 ppm, 20 % [D 6 ]DMSO in CD 3 CN) are observed between the enantiomers of 4 upon addition of [ n Bu 4 N][ Δ ‐ 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 ‐(SO 4 ) 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 ][SO 4 ] 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.