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Russian Nesting Doll Complexes of Molecular Baskets and Zinc Containing TPA Ligands

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journal contribution
posted on 15.06.2016 by Lei Zhiquan, Shane Polen, Christopher M. Hadad, T. V. RajanBabu, Jovica D. Badjić
In this study, we examined the structural and electronic complementarities of convex 1–Zn­(II), comprising functionalized tris­(2-pyridylmethyl)­amine (TPA) ligand, and concave baskets 2 and 3, having glycine and (S)-alanine amino acids at the rim. With the assistance of 1H NMR spectroscopy and mass spectrometry, we found that basket 2 would entrap 1–Zn­(II) in water to give equimolar 1–Zn⊂2in complex (K = (2.0 ± 0.2) × 103 M–1) resembling Russian nesting dolls. Moreover, C3 symmetric and enantiopure basket 3, containing (S)-alanine groups at the rim, was found to transfer its static chirality to entrapped 1–Zn­(II) and, via intermolecular ionic contacts, twist the ligand’s pyridine rings into a left-handed (M) propeller (circular dichroism spectroscopy). With molecular baskets embodying the second coordination sphere about metal-containing TPAs, the here described findings should be useful for extending the catalytic function and chiral discrimination capability of TPAs.