Synthesis and characterization of bis-[1]rotaxanes viasalen-bridged bis-pillar[5]arenes

The series of salen-bridged bis-pillar[1]arenes were conveniently prepared by condensation reaction of 5,5′-methylenebis(2-hydroxybenzaldehyde) or 5,5′-(propane-2,2-diyl)bis(2-hydroxybenzaldehyde) with mono-amido-functionalized pillar[5]arenes. The 1H NMR and 2D-NOESY spectra as well as single crystal structure clearly indicated that the salen-bridged bis-pillar[5]arenes with longer alkylene linker (m = 0, 1, 3) formed the fascinating bis-[1]rotaxanes, while those with short hydrazine and ethylenediamino linker predominately existed in free form.