Kinetic Control of Threading and Dethreading in Linked Rotaxanes via Hydrogen Bonding.

Abstract

The kinetic control of macrocyclic motions is a key aspect of mechanically interlocked molecules (MIMs). Although hydrogen bonding (H-bonding) offers a high reversibility and selectivity, the use of neutral H-bonding to control the macrocyclic mobility remains limited. In this study, the effects of H-bonding on the threading and dethreading kinetics of linked rotaxanes containing a permethylated α-cyclodextrin unit and an aniline moiety were investigated. UV-Vis spectroscopy revealed significantly reduced reaction rates in H-bond acceptor solvents, such as dimethyl sulfoxide (DMSO) and dimethyl formamide. NMR titrations and FT-IR spectroscopic analyses confirmed that H-bonding between the aniline moiety and these solvents acts as a "brake" during threading/dethreading. Moreover, Eyring plots indicated that enthalpic losses during H-bond cleavage contribute to the increased activation barriers for these processes. Additionally, the introduction of H-bond acceptors, such as DMSO and tributylphosphine oxide, effectively modulated these rates of threading and dethreading, highlighting the potential for controlling kinetic phenomena in MIM-based systems.