Macrocycle shuttling

A [2]rotaxane containing two degenerate and well-separated stations on its thread can be considered the simplest example to study the shuttling phenomenon [40]. In such a system the macrocycle shuttles back and forth... 

FIGURE 19.10 A typical rotaxane shuttle set-up. The macrocycle encircles the thread-like portion of the dumbbell with heavy groups at its ends. The thread has two recognition sites which can be altered reversibly so as to make the macrocycle shuttle between the two sites (state 0 and state 1). 

The possibility of fine-tuning electron transfer processes through molecular shuttling was finally shown by introducing ferrocene electron donors on the macrocycle (Scheme 9.13).56... 

If during the template-directed synthesis of a rotaxane, the location of two identical recognition sites ( stations ) within its dumbbell component can be arranged (Fig. 13.3a and b), a degenerate, coconformational equilibrium state is obtained in which the macrocyclic component spontaneously shuttles back and forth between... 

Structurally related to these species are the triply branched compound 56+ and its rotaxanes 66+, 76+, and 86+ (Fig. 13.6)9, in which one, two, or three acceptor units are encircled by the electron donor macrocyclic compound 2. Although these rotaxanes cannot behave as degenerate molecular shuttles because of their branched topology, they are nevertheless interesting from the electrochemical viewpoint. 

Rotaxane 316+ was specifically designed36 to achieve photoinduced ring shuttling in solution,37 but it also behaves as an electrochemically driven molecular shuttle. This compound has a modular structure its ring component is the electron donor macrocycle 2, whereas its dumbbell component is made of several covalently linked units. They are a Ru(II) polypyridine complex (P2+), ap-terpheny 1-type rigid spacer... 

Figure 14.15 Second copper-based molecular shuttle 10(4) +, containing a sterically nonhindering macrocycle.

Scheme 15.9 Reversible shuttling of the benzylic amide macrocycle in [2]rotaxane 53 by redox reactions.

FIGURE 3.5 A molecular shuttle. The "bead", consisting of a macrocycle containing four pyridine rings and two benzene rings, moves back and forth between the two "stations", which are benzene rings. The "stoppers" prevent the bead from falling off the chain.1,5... 

Figure 6.8 Structural formula of the rotaxane 96+ and schematic representation of the intramolecular (below left) and sacrificial (below right) mechanisms for the photoinduced shuttling movement of macrocycle between the two stations A1 and A2.

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