Controlling the Molecular Shuttling of pH-Responsive [2]Rotaxanes with Two Different Stations

A novel synthesis of degenerate [2]rotaxanes with two different amine stations is presented. Variable-temperature H-1 NMR and rotating-frame nuclear Overhauser effect correlation spectroscopy experiments revealed that the addition of trifluoroacetic acid initiates molecular shuttling. The activation barrier for the motion remained constant even when the amine in the outer station was changed. Conversely, the addition of camphorsulfonic acid caused a rotational motion, which was demonstrated by synthesizing a new [2]rotaxane without an outer station and examining its molecular behavior in the presence of acid.

Automated summary

A new method for the synthesis of degenerate [2]rotaxanes with two different amine stations is presented in this study. The addition of trifluoroacetic acid was found to initiate molecular shuttling, as revealed by variable-temperature H-1 NMR and rotating-frame nuclear Overhauser effect correlation spectroscopy experiments. The activation barrier for the motion remained constant even with different amines in the outer station. Conversely, the addition of camphorsulfonic acid caused rotational motion, as demonstrated by synthesizing a new [2]rotaxane without an outer station and examining its molecular behavior in the presence of acid.