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

Abstract

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 Δ and Λ-enantionomers of the Ru(II) trisdiimine complexes and derivatized CDs is readily observed by NMR. In particular, sulfobutyl ether-β-cyclodextrin sodium salt (SBE-β-CD), R-naphtylethyl carbamate β-cyclodextrin (RN-β-CD), and S-naphtylethyl carbamate β-cyclodextrin (SN-β-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.

1H NMR assignment corrections and 1H, 13C, 15N NMR coordination shifts structural correlations in Fe(II), Ru(II) and Os(II) cationic complexes with 2,2′‐bipyridine and 1,10‐phenanthroline

“…We have found, for all metals and solvents, the following signal orders: H(3) > H(4) > H(5)/H(6) for [M(bpy) 3 ] 2+ and H(4) > H(5) > H(2) > H(3) for [M(phen) 3 ] 2+ (Table 1), which are entirely different from those for free bpy [H(6) > H(3) > H(4) > H(5)] or phen [H(2) > H(4) > H(5) > H(3)]. They are in agreement with the orders proposed for [Ru(phen) 3 ]Cl 2 and [Os(phen) 3 ]Cl 2 in the articles,7, 26, 27, 31 but not with those suggested for [Fe(bpy) 3 ]Cl 2 , [Ru(bpy) 3 ]Cl 2 , [Os(bpy) 3 ]Cl 2 and [Ru(phen) 3 ]Cl 2 in the articles1, 4–7, 25 (the spectra of [Ru(bpy) 3 ]Cl 2 and [Ru(phen) 3 ]Cl 2 , described in the works,46, 47 remained unassigned) (Table S1, Supplementary Information). Independent of the correctness of these inconsistent assignments, we have observed relatively large δ 1H variability (up to ca 0.65 ppm) when comparing all available data (including ours and the literature ones: see Tables 1 and S1), even in the same solvents; in our opinion, it results from the different strength of solvation effects and cation–anion interactions at various concentrations.…”

“…The 1 H NMR spectra for the studied [M(LL) 3 ]Cl 2 complexes (M = Fe, Ru, Os; LL = bpy, phen) were reported by several authors; however, their assignments were inconsistent or uncertain 1, 4–7, 25–27, 31, 46, 47. We have measured and assigned all of them in D 2 O (basing on the 1 H‐ 13 C and 1 H‐ 15 N correlations; the 1 H‐ 13 C HSQC and HMBC spectra are exemplified for [Fe(bpy) 3 ]Cl 2 and [Fe(phen) 3 ]Cl 2 in D 2 O—Figures S1–S4, Supplementary Information), as well as in DMSO‐ d 6 and CD 3 CN (by analogy to the results in D 2 O).…”

“…The 1 H NMR data for their salts were assigned in case of [Fe(bpy) 3 ]Cl 2 ,1 [Fe(bpy) 3 ](ClO 4 ) 2 ,2 [Fe(bpy) 3 ](PF 6 ) 2 ,3 [Ru(bpy) 3 ] Cl 2 ,4–7 [Ru(bpy) 3 ](SCN) 2 ,8 [Ru(bpy) 3 ](ClO 4 ) 2 ,2, 9 [Ru(bpy) 3 ] (PF 6 ) 2 ,10–18 [Ru(bpy) 3 ](BF 4 ) 2 ,19, 20 [Os(bpy) 3 ]Cl 2 ,5 [Os(bpy) 3 ] (ClO 4 ) 2 ,2, 21 [Os(bpy) 3 ](PF 6 ) 2 22 and [Fe(phen) 3 ](ClO 4 ) 2 ,23, 24 [Ru(phen) 3 ]Cl 2 ,7, 25–27 [Ru(phen) 3 ](ClO 4 ) 2 ,9, 14, 24, 28 [Ru(phen) 3 ] (PF 6 ) 2 ,29 [Ru(phen) 3 ](BF 4 ) 2 ,19 [Ru(phen) 3 ]SO 4 ,30 [Os(phen) 3 ] Cl 2 ,31 [Os(phen) 3 ](CF 3 SO 3 ) 2 32. It is really surprising, however, that their assignments were inconsistent, although the spectral patterns of such highly symmetric [M(LL) 3 ] 2+ cations were relatively simple, containing two doublets [H(3)/H(6)] and two triplets [H(4)/H(5)] for LL = bpy, or two doublets [H(2)/H(4)], a doublet of doublets [H(3)] and a singlet [H(5)] for LL = phen.…”

“…It is really surprising, however, that their assignments were inconsistent, although the spectral patterns of such highly symmetric [M(LL) 3 ] 2+ cations were relatively simple, containing two doublets [H(3)/H(6)] and two triplets [H(4)/H(5)] for LL = bpy, or two doublets [H(2)/H(4)], a doublet of doublets [H(3)] and a singlet [H(5)] for LL = phen. Particularly, the predominantly suggested orders of the 1 H resonances, H(3) > H(4) > H(5)/H(6) for [M(bpy) 3 ] 2+ 2, 3, 8–13, 15–17, 19–22 and H(4) > H(5) > H(2) > H(3) for [M(phen) 3 ] 2+ ,7, 9, 24, 26–28, 30, 31 contrasted to those proposed by some other authors: H(6) > H(3) > H(4) > H(5),1 H(6) > H(4) > H(3) > H(5),4 H(6) > H(5) > H(3) > H(4),5–7 H(3) > H(6) > H(5) > H(4)14 (all for [M(bpy) 3 ] 2+ ) and H(4) > H(2) > H(5) > H(3),29 H(2) > H(4) > H(3) > H(5),14 H(2) > H(3) > H(4) > H(5),19 H(2) > H(5) > H(4) > H(3),23, 32 H(2) > H(4) > H(5) > H(3)25 (all for [M(phen) 3 ] 2+ ). In our opinion, very large variations cannot be caused by the change of solvent and/or counterions, but they reflect erroneous attributions in some articles (the largest differences concerned peaks with the same multiplicity: H(3)/H(6) and H(4)/H(5) in bpy; H(2)/H(4) in phen).…”

Nonaqueous capillary gel electrophoretic analysis of metal nanoclusters in polymeric–DMSO–Li+ systems

“…In the present article, we investigated the combination of nonaqueous CE (NACE) and capillary gel electrophoresis (CGE), that is, nonaqueous capillary gel electrophoresis (NACGE), to separate the nanoclusters. Because CGE is known as highly effective separation method for DNA [6], RNA [7,8], and metal complexes [9][10][11], it is expected that NACGE is suitable for separating closely related metal complexes and their impurities in organic solvent BGE. However, only a few reports on NACGE have appeared so far.…”