Modulating the binding of polycyclic aromatic hydrocarbons inside a hexacationic cage by anion-π interactions

Nema Hafezi, James M. Holcroft, Karel J. Hartlieb, Edward J. Dale, Nicolaas A. Vermeulen, Charlotte L. Stern, Amy A. Sarjeant, J. Fraser Stoddart

Research output: Contribution to journalArticlepeer-review

54 Scopus citations

Abstract

We report the template-directed synthesis of Blue-Cage6+, 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·6PF6 exhibits a lower association constant Ka than its progenitor ExCage·6PF6. 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.

Original languageEnglish (US)
Pages (from-to)456-461
Number of pages6
JournalAngewandte Chemie - International Edition
Volume54
Issue number2
DOIs
StatePublished - Jan 7 2015

Keywords

  • Cage compounds
  • Cyclophanes
  • Host-guest complexes
  • Supramolecular chemistry

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

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