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Catalysis of an Aldol Condensation Using a Coordination Cage

Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK
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Chemistry 2020, 2(1), 22-32; https://doi.org/10.3390/chemistry2010004
Received: 7 January 2020 / Revised: 22 January 2020 / Accepted: 24 January 2020 / Published: 25 January 2020
(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)
The aldol condensation of indane-1,3-dione (ID) to give ‘bindone’ in water is catalysed by an M8L12 cubic coordination cage (Hw). The absolute rate of reaction is slow under weakly acidic conditions (pH 3–4), but in the absence of a catalyst it is undetectable. In water, the binding constant of ID in the cavity of Hw is ca. 2.4 (±1.2) × 103 M−1, giving a ∆G for the binding of −19.3 (±1.2) kJ mol−1. The crystal structure of the complex revealed the presence of two molecules of the guest ID stacked inside the cavity, giving a packing coefficient of 74% as well as another molecule hydrogen-bonded to the cage’s exterior surface. We suggest that the catalysis occurs due to the stabilisation of the enolate anion of ID by the 16+ surface of the cage, which also attracts molecules of neutral ID to the surface because of its hydrophobicity. The cage, therefore, brings together neutral ID and its enolate anion via two different interactions to catalyse the reaction, which—as the control experiments show—occurs at the exterior surface of the cage and not inside the cage cavity. View Full-Text
Keywords: host–guest chemistry; coordination cage; catalysis; crystal structure; supramolecular chemistry host–guest chemistry; coordination cage; catalysis; crystal structure; supramolecular chemistry
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Mozaceanu, C.; Taylor, C.G.P.; Piper, J.R.; Argent, S.P.; Ward, M.D. Catalysis of an Aldol Condensation Using a Coordination Cage. Chemistry 2020, 2, 22-32.

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