<i>Tris</i>-<i>N</i>-alkylpyridinium-functionalised cyclotriguaiacylene hosts as axles in branched [4]pseudorotaxane formation

A series of [4]pseudorotaxanes composed of three-way axle threads based on the cyclotriguaiacylene family of crown-shaped cavitands and three threaded macrocyclic components has been achieved. These exploit the strong affinity for electron-poor alkyl-pyridinium units to reside within the electron-rich cavity of macrocycles, in this case dimethoxypillar[5]arene (DMP). The branched [4]pseudorotaxane assemblies {(DMP)₃∙<i>L</i>}³⁺,where <i>L</i> = <i>N</i>-alkylated derivatives of the host molecule (±)-<i>tris</i>-(isonicotinoyl)cyclotriguaiacylene, were characterised by NMR spectroscopy and mass spectrometry, and an energy-minimised structure of {(DMP)₃∙(<i>tris</i>-(<i>N</i>-propyl-isonicotinoyl)cyclotriguaiacylene)}³⁺ was calculated. Crystal structures of <i>N</i>-ethyl-isonicotinoyl)cyclotriguaiacylene hexafluorophosphate and <i>N</i>-propyl-isonicotinoyl)cyclotriguaiacylene hexafluorophosphate each show ‘hand-shake’ self-inclusion motifs occurring between the individual cavitands.