Fixing the conformation of calix[4]arenes: When are three carbons not enough?

Susan Matthews, Samy Cecioni, John O'Brien, Colin MacDonald, David Hughes, Garth Jones, Stephen Ashworth, Sebastien Vidal

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)
13 Downloads (Pure)

Abstract

Calix[4]arenes are unique macrocycles that through judicious functionalisation at the lower-rim can be either fixed in one of four conformations or remain conformationally flexible. Introduction of propynyl or propenyl groups unexpectedly provides a new possibility; a unidirectional conformational switch, with the 1,3-alternate and 1,2-alternate conformers switching to the partial cone conformation, whilst the cone conformation is unchanged, under standard experimental conditions. Using 1H NMR kinetic studies, rates of switching have been shown to be dependent on the starting conformation, upper-rim substituent, where reduction in bulk enables faster switching, solvent and temperature with 1,2-alternate conformations switching fastest. Ab initio calculations (DFT) confirmed the relative stabilities of the conformations and point towards the partial cone conformer being the most stable of the four. The potential impact on synthesis through the ‘click’ reaction has been investigated and found not to be significant.
Original languageEnglish
Pages (from-to)4436-4444
Number of pages9
JournalChemistry - A European Journal
Volume24
Issue number17
Early online date16 Jan 2018
DOIs
Publication statusPublished - 20 Mar 2018

Keywords

  • NMR spectroscopy
  • Calixarenes
  • macrocycles
  • Kinetics
  • conformational analysis

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