Rotaxanes synthetic

Another synthetic strategy is based on self-assembly driven by molecular recognition between complementary TT-donors and 7T-acceptors. Examples include the synthesis of catenanes and rotaxanes that can act as controUable molecular shuttles (6,236). The TT-donors in the shuttles are located in the dumb-beU shaped component of the rotaxane and the 7T-acceptors in the macrocycHc component, or vice versa. The shuttles may be switched by chemical, electrochemical, or photochemical means. 

MacrocycHc isophthalamides (the tetralactam macrocycles) have been used as a host to build rotaxanes and catenanes by Vogtle and others [15]. Structurally analogous to cyclophanes, their initial usage as a synthetic receptor was for... 

R. Jager, F. Vogtle, A New Synthetic Strategy towards Molecules with Mechanical Bonds Nonionic Template Synthesis of Amide-Linked Catenanes and Rotaxanes , Angew. Chem Int. Ed. Engl. 1997,36,930-944. 

Rationale and efficient synthetic approaches for the preparation of complicated (supra)molecular systems like pseudorotaxanes, rotaxanes and catenanes have been devised only recently.1171 The strategies chosen by Stoddart and coworkers1181 are based... 

Rotaxanes maybe prepared using several different synthetic strategies which are summarized in Scheme 12. 

The [2]rotaxanes, which contain tetrathiafulvalene (TTF) and 1,5-dioxynaphtha-lene (DNP) as the two recognition stations and cyclobis(paraquat-p-phenylene) (CBPQT4 + ) as the cyclic moiety, have been comprehensively investigated by Stoddart and coworkers.68 We have recently reported two new TTF-DNP-CBPQT4+ [2]rotaxanes 62 and 63. In these two [2]rotaxanes, the TTF moiety is the 4,4 (5 )-dialkylthiotetrathiafulvalene that is rather easily accessible based on the synthetic procedure developed by us previously,69 and two different spacers are used the cyclohexyl and alkyl chains. Two stopper units are the G2-dendritic moieties. 

Figure 1. Threading (a and b) and slipping (c) approaches to [2]iotaxanes. Clipping (not shown) is another synthetic approach to rotaxanes. It involves the macrocyclization of the ring component around the preformed dumbbell-shaped component.

The great synthetic potential of the covalent linkage of catenanes and rotaxanes via sulfonamide groups in such a way enables the chemist to construct larger topologically interesting assemblies and to aim at nanoscale architectures. 

The great variety of incorporable building blocks also offers the synthetic chemist many potential structural and functional design possibilities. The insertion of, e.g., photo-responsive elements, groups with further supramolecular derivatization potential, or sulfonamide units which enable subsequent inter- and intramolecular linkage of catenanes and rotaxanes might render good service in the development of molecular switches [64] and devices [65]. 

The principle of the second synthetic approach to polycatenanes, i.e. stepwise polycondensation, has been proposed by Shaffer and Tsay, but not experimentally demonstrated [42, 43], This approach has the advantage over multifunctional polycondensation that a linear polymer is formed before cyclization (Scheme 7). However, the second step, which consists of the cyclization of n macrocycles along the polymer chain 19, is likely, again, to give rise to an undefined network, containing some rotaxane and catenane units 21, similar to the multifunctional polycondensation approach. 

IX. Problems and Solutions A Synthetic Approach to Rotaxanes with... 

IX. PrnhlRms and Solutions A Synthetic Approach to Rotaxanes with Functional ( roups in (he Axle On ter piece... 

One highly interesting feature of this synthetic approach is that rotaxanes are generated that contain a functional group at their axle centers. This permits to control the rotaxanes properties by external stimuli, e.g. by protonation and deprotonation. 

Interlocked molecules such as rotaxanes initially gained interest due to their interesting topology and associated synthetic challenge, but recent efforts have showed that they can be used in many important applications that will be discussed in this chapter (Scheme 6.1). 

The first rotaxanes were prepared by a statistical synthetic approach. The threading of a macrocycle around a linear chain is based purely on chance no specific... 

The development of good synthetic methods for the preparation of rotaxanes in moderate to good yields has opened new ways to explore the physical properties... 

The rotaxane assembly is adopted by many enzymes that operate on nucleic acids and proteins. In the case of processive enzymes, the catalytic reaction drives the sequential motion of the enzyme on its polymeric substrate. Therefore, these enzymes can be viewed as molecular motors powered by chemical reactions and moving one-dimensionally on a track, in which fuel is provided by the track itself. An initial attempt to carry out processive catalysis with a synthetic rotaxane has been described [69]. 

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