Tris-N-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)center dot L}(3+) ,where L = N-alkylated derivatives of the host molecule (+/-)-tris-(isonicotinoyl)cyclotriguaiacylene, were characterised by NMR spectroscopy and mass spectrometry, and an energy-minimised structure of {(DMP)(3)center dot(tris-(N-propyl-isonicotinoyl)cyclotriguaiacylene)}(3+) was calculated. Crystal structures of N-ethyl-isonicotinoyl) cyclotriguaiacylene hexafluorophosphate and N-propyl-isonicotinoyl)cyclotriguaiacylene hexafluorophosphate each show 'hand-shake' self-inclusion motifs occurring between the individual cavitands. [GRAPHICS]