Slippage - A simple and efficient way to self-assemble [n]rotaxanes

Slippage is a relatively simple phenomenon that provides an efficient way to self-assemble [n]rotaxanes. The procedure is based on the size complementarity between the dumbbell-shaped and macrocyclic components of the rotaxane. The macrocycle has to possess a cavity that is just large enough to slip over the bulky stoppers attached to both ends of the dumbbell-shaped component under the influence of an appropriate amount of thermal energy. A series of cooperative noncovalent bonding interactions between complementary recognition sites incorporated within the macrocyclic and dumbbell-shaped components are then responsible for stabilising the resulting assembly - namely a rotaxane. The kinetics of the so-called slippage approach to rotaxanes have been investigated by varying systematically the sizes of the macrocycles as well as the sizes of the stoppers attached to the ends of the dumbbell-shaped components. The potential of this approach to self-assemble kinetically- and thermodynamically-stable molecular compounds has been demonstrated with the production of numerous linear and branched [2]-, [3]-, and [4]-rotaxanes, as well as with the stepwise construction of a linear [3]rotaxane incorporating a dumbbell-shaped component encircled by two constitutionally different macrocyclic components.