Unraveling the molecular recognition of “three methylene spacer” bis(benzimidazolium) moiety by dibenzo-24-crown-8: pseudorotaxanes under study

Abstract

“Three methylene spacer” bis(benzimidazolium) derivatives act as a new template for threading dibenzo-24-crown-8 into [2]pseudorotaxanes. In this Article we sought to unveil the difference in the extent of threading of various “three methylene spacer” bis-benzimidazolium moieties based on differences in aromatic methyl substituent positions and anions through the macrocycle dibenzo-24-crown-8. The temperature of the systems were also varied (low temperatures of 240 K and 253 K), when such interwinding of the thread and crown were not detected at room temperature of 308 K. The presence of such threaded complexes was determined based on ¹H-NMR initially and finally corroborated by high resolution mass spectrometry and DFT calculations. 2D-NMR experiments (¹H–¹H-NOESY) proved to be a very important tool in elucidating the interaction present between the components of the pseudorotaxanes. The dethreading/rethreading process was studied. DFT optimized structures suggest lower energy H-bonding orientations and compare the effect of methyl substituents on the axle.