Highly Efficient NMR Enantiodiscrimination of Chiral Octanuclear Metalla-Boxes in Polar Solvent

Self-assembly of 5,10,15,20-tetra(4-pyridyl)porphyrin (tpp-H2) and 5,10,15,20-tetra(4-pyridyl)porphyrin-Zn(II) (tpp-Zn) tetradentate panels with the dinuclear p-cymene ruthenium clips [Ru26-p-PriC6H4Me)2(μ-C2O4-κO)Cl2] and [Ru26-p-PriC6H4Me)2(μ-C6H2O4-κO)Cl2] (C2O4 = oxalato; C6H2O4 = 2,5-dihydroxy-1,4-benzoquinonato) affords the cationic organometallic boxes [Ru86-p-PriC6H4Me)84-tpp-H2-κN)2(μ-C2O4-κO)4]8+ ([1]8+), [Ru86-p-PriC6H4Me)84-tpp-H2-κN)2(μ-C6H2O4-κO)4]8+ ([2]8+), [Ru86-p-PriC6H4Me)84-tpp-Zn-κN)2(μ-C2O4-κO)4]8+ ([3]8+), and [Ru86-p-PriC6H4Me)84-tpp-Zn-κN)2(μ-C6H2O4-κO)4]8+ ([4]8+). In solution, for all these complexes, a rapid and effective enantiodifferentiation was achieved in the presence of the NMR chiral solvating agent Λ-BINPHAT anion, only 0.05 to 0.10 equiv being necessary for complete baseline-to-baseline separation of some of the proton signals of the enantiomers. To add to this highly effective discrimination, all experiments were performed in the high-polarity solvent CD3CN, a solvent traditionally not favorable for effective chiral ion-pairing phenomena.