Modulating the Binding of Polycyclic Aromatic Hydrocarbons Inside a Hexacationic Cage by Anion–π Interactions |
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| Authors: | Dr Nema Hafezi Dr James M Holcroft Dr Karel J Hartlieb Edward J Dale Dr Nicolaas A Vermeulen Charlotte L Stern Dr Amy A Sarjeant Prof J Fraser Stoddart |
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| Institution: | Center for the Chemistry of Integrated Systems, Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (USA) |
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| Abstract: | We report the template‐directed synthesis of BlueCage6+, a macrobicyclic cyclophane composed of six pyridinium rings fused with two central triazines and bridged by three paraxylylene units. These moieties endow the cage with a remarkably electron‐poor cavity, which makes it a powerful receptor for polycyclic aromatic hydrocarbons (PAHs). Upon forming a 1:1 complex with pyrene in acetonitrile, however, BlueCage?6 PF6 exhibits a lower association constant Ka than its progenitor ExCage?6 PF6. A close inspection reveals that the six PF6? counterions of BlueCage6+ occupy the cavity in a fleeting manner as a consequence of anion–π interactions and, as a result, compete with the PAH guests. This conclusion is supported by a one order of magnitude increase in the Ka value for pyrene in BlueCage6+ when the PF6? counterions are replaced by much bulkier anions. The presence of anion–π interactions is supported by X‐ray crystallography, and confirms the presence of a PF6? counterion inside its cavity. |
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| Keywords: | cage compounds cyclophanes host– guest complexes supramolecular chemistry |
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