Chiral metal complexes. 5. Sources of chiral discrimination in aqueous solutions of the complexes Δ,Λ-[Ru(diimine)2(L-aspartate)]° and their conjugate acids

Terence J. Goodwin, Peter A. Williams*, Robert S. Vagg

*Corresponding author for this work

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Abstract

The complex ternary species Δ,Λ-[Ru(phen)2(L-asp)]°, Δ,Λ-[Ru(phen)2(L-aspH)]+ and their bipy analogues (L-aspH2 = L-aspartic acid, phen = 1,10-phenanthroline, bipy = 2,2′-bipyridyl) have been synthesised and characterized, and the various diastereoisomers separated using cation exchange chromatography. Equilibrium constants in H2O solution for the reaction Δ-[Ru(diimine)2(L-aa)]n+ qa ⇌Λ-[Ru(diimine)2(L-aa)]n+ (aq), L-aa being either [L- asp]2- or ([L-aspH]-, are 1.00(1), 1.39(1), 0.88(1) and 1.22(1), respectively at 298.2 K. In D2O, the corresponding values are 1.52(10), 1.50(4), 1.09(3) and 1.21(9). High resolution 1H nmr studies indicate that a strong intramolecular hydrogen bond between the uncoordinated carboxyl group and an amine hydrogen atom of the amino acid exists when the species are deprotonated, and that this effects the relative thermodynamic stabilities of the diastereoisomers. Equilibration differences in H2O and D2O suggest the possibility of hydrophobic bonding being a source of chiral discriminations in complexes of this type. Such discriminations, although small in magnitude, arising from the above interactions and steric effects are discussed.

Original languageEnglish
Pages (from-to)133-140
Number of pages8
JournalInorganica Chimica Acta
Volume63
Issue numberC
DOIs
Publication statusPublished - 1982

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