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 [Ru₂(η⁶-p-PrⁱC₆H₄Me)₂(μ-C₂O₄-κO)Cl₂] and [Ru₂(η⁶-p-PrⁱC₆H₄Me)₂(μ-C₆H₂O₄-κO)Cl₂] (C₂O₄ = oxalato; C₆H₂O₄ = 2,5-dihydroxy-1,4-benzoquinonato) affords the cationic organometallic boxes [Ru₈(η⁶-p-PrⁱC₆H₄Me)₈(μ₄-tpp-H₂-κN)₂(μ-C₂O₄-κO)₄]⁸⁺ ([1]⁸⁺), [Ru₈(η⁶-p-PrⁱC₆H₄Me)₈(μ₄-tpp-H₂-κN)₂(μ-C₆H₂O₄-κO)₄]⁸⁺ ([2]⁸⁺), [Ru₈(η⁶-p-PrⁱC₆H₄Me)₈(μ₄-tpp-Zn-κN)₂(μ-C₂O₄-κO)₄]⁸⁺ ([3]⁸⁺), and [Ru₈(η⁶-p-PrⁱC₆H₄Me)₈(μ₄-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.