Ring-Over-Ring Deslipping From Imine-Bridged Heterorotaxanes.

Ring-over-ring slippage and ring-through-ring penetration are important processes in the construction of ring-in-ring multiple interlocked architectures. We have successfully observed "ring-over-ring deslipping" on the rotaxane axle by exploiting the dynamic covalent nature of imine bonds in imine-bridged heterorotaxanes and with two macrocycles of different ring sizes on the axle. When the imine bridges of were cleaved, a hydrolyzed hetero[4]rotaxane was formed as an intermediate under dynamic equilibrium, and the larger 38-membered macrocycle was deslipped over the 24-membered ring (24C8 or DB24C8) to dissociate into a [3]rotaxane and a macrocycle . The time dependent NMR measurement and the determined thermodynamic parameters revealed that the rate-limiting step of the deslipping process was attributed to steric hindrance between two rings and reduced mobility of due to proximity to the crown ether, which was bound to the anilinium on the axle molecule.