Enantioselective host-guest complexation of Ru(II) trisdiimine complexes using neutral and anionic derivatized cyclodextrins

摘要

Enantioselective host-guest complexation between five racemic Ru(II) trisdiimine complexes and eight derivatized cyclodextrins (CDs) has been examined by NMR techniques. The appearance of non-equivalent complexation-induced shifts of between the A and A-enantionomers of the Ru(II) trisdiimine complexes and derivatized CDs is readily observed by NMR. In particular, sulfobutyl ether-p-cyclodextrin sodium salt (SBE-13-CD), R-naphtylethyl carbamate p-cyclodextrin (RN-I3-CD), and S-naphtylethyl carbamate p-cyclodextrin (SN-p-CD) showed good enantiodiscrimination for all five Ru complexes examined, which indicates that aromatic and anionic derivatizing groups are beneficial for chiral recognition. The complexation stoichiometry between SBE-β-CD and [Ru(phen)_3]~(2+) was found to be 1:1 and binding constants reveal that Λ-[Ru(phen)_3]~(2+) binds more strongly to SBE-β-CD than the Δ-enantiomer. Correlations between this NMR method and separative techniques based on CDs as chiral discriminating agents (i.e., selectors) are discussed in detail.