Modulating the Binding of Polycyclic Aromatic Hydrocarbons Inside a Hexacationic Cage by Anion–π Interactions1. Issue 2 (19th November 2014)

• Record Type: Journal Article
• Authors: Hafezi, Nema; Holcroft, James M.; Hartlieb, Karel J.; Dale, Edward J.; Vermeulen, Nicolaas A.; Stern, Charlotte L.; Sarjeant, Amy A.; Stoddart, J. Fraser
• Is Part Of: Angewandte Chemie international edition. Volume 54:Issue 2(2015)
• Page Start: 456
• Page End: 461
• Publication Date: 2014-11-19
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201408400
• Languages: English
• ISSNs: 1433-7851

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>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 <italic>K</italic>_a 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 <italic>K</italic>_a 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.</p> </abstract>