Template 3 rotaxanes

Scheme 10.16 Anion-templated [2]rotaxane and [2]catenane formation reported by Beer and coworkers.

One of the several ammonium-templated rotaxanes reported by Stoddart [56] is based on a threadlike ammonium species with terminal azido-groups (19). Upon mixing this axle with crown ether 20, the [2]pseudorotaxane 21 was formed (see Scheme 13). 

Scheme 16 anion-templated rotaxane synthesis via a Michael addition reaction. 

Schalley, C.A, Silva, G., Nising, C.F., Linnartz, P. Analysis and improvement of an anion-templated rotaxane synthesis, Helv. Chim. Acta, 85 (2002), 1578-1596. 

To overcome this difficulty, a new solution is developed that involves spatial separation of the functional group for stopper attachment from the phenolate that provides the basis for anion template. Rotaxanes can be synthesized with yields up to 45% [32] (Figure 11). 

Fig. 1.4. Anion-templated rotaxane synthesis. The axle center piece is threaded through the macrocycle s cavity by hydrogen bonding. Stopper attachment to both axle ends traps the wheel on the axle. Inset hydroquinone-based center piece which can also be used, but with lower efficiency.

Fig.l Self-assembly of anion templated rotaxane SAM (RC = redox centre). From [46], reproduced by permission of The Royal Society of Chemistry... 

Analysis and improvement of an anion-templated rotaxane synthesis. Helv. Chim. Acta, 2002. 85. 1578. 

Figure 37 Principle of the photochemically and chemically triggered rearrangement of the copper(I) complex-templated rotaxane. (Reproduced from Ref. 71. American Chemical Society, 1999.)...

Template synthesis and chirality of catenanes, rotaxanes, and pretzelanes including N-macroheterocyclic lactams and related compounds as structure components 99PAC247. 

Nonionic template synthesis of amide-linked catenanes and rotaxanes with macroheterocyclic fragments 97AG(E)930. 

Schalley CA, WeUandt T, Briiggemann J,V6gtle F (2004) Hydrogen-Bond-Mediated Template Synthesis of Rotaxanes, Catenanes, and Knotanes. 248 141-200 Scheer M,see Balazs G (2003) 232 1-23... 

Template effects have been used in rotaxane synthesis to direct threading of the axle through the wheel. Since macrocycHc compounds such as cyclodextrins, crown ethers, cyclophanes, and cucurbiturils form stable complexes with specific guest molecules, they have been widely used in the templated synthesis of rotax-anes as ring (wheel) components. Here, we briefly discuss macrocycles used in the synthesis of rotaxane dendrimers and their important features. 

In this review, we tried to cover all the supramolecular species that maybe classified as rotaxane dendrimers. We classified them by their structures - where in dendrimer rotaxane-hke features are introduced. Several different types of macrocycles have been employed as a ring component in the templated synthesis of rotaxane dendrimers. While the synthesis of Type I and II rotaxanes dendrimers is relatively straightforward, that of well-defined Type III rotaxane dendrimers, particularly those of second and higher generations, is still challenging. 

Other supramolecular structures such as catenanes and rotaxanes can be formed using zinc as a template ion for example, a benzylic imine catenate formed by Leigh et a/.288 The reversible five-component assembly of a [2]catenane from a chiral metallomacrocycle and a dinaphtho-crown ether has been achieved. Zinc is used as the metal component and drives assembly via the coordination to a bipyridyl unit 7r interactions between the aromatic components are also... 

Blanco, M.-J., Transition-Metal-Templated Synthesis of Rotaxanes, 23, 125. 

A useful summary of the various and numerous types of rotaxanes, catenanes, and knots can be found in a review of template routes to interlocked molecular structures 468). Inorganic chemistry is centrally involved in the templating involved in self-assembly and in controlled synthesis of such species. 

Pseudorotaxanes are precursors of both rotaxanes and catenanes they consist of a guest molecule threaded through a macrocyclic host. Stoppering both ends of the threaded molecule gives a rotaxane, cycliza-tion of the thread gives a catenane. Pseudorotaxane formation may occur by spontaneous self-assembly, or may be template-controlled. Anion size can be of paramount importance for such templates - Cl- is effective, Br, I- less good, and PFe ineffective when the recognition motif demands a small template (454). 

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. 

As will be discussed later, ammonium salts have also been used as hydrogen bond-donor templates to favour the formation of macrocycles (yielding pseu-dorotaxanes and rotaxanes). 

The strong hydrogen bonding interactions observed between the oxygen atoms of crown ethers and the N-H groups of ammonium groups can be successfully employed to prepare pseudorotaxanes and rotaxanes by templated processes. This approach has been extensively utilised by Stoddart, Busch and others to obtain a wide range of interlocked species. 

Scheme 13 Templated synthesis of rotaxane 22 employing the threading-followed-by-capping methodology...

Scheme 15 Templated synthesis of rotaxane 24 employing the threading-followed-by-capping methodology. The shift of the proton from the terminal amine to the secondary amine allows for the threading to occur yielding the pseudorotaxane 26... 

The threading-followed-by-capping method has been recently employed by Stoddart to prepare a [2]rotaxane under thermodynamic control [60]. In this approach, the dibenzylammonium ion 28 - which is terminated by an aldehyde function - is mixed with the dibenzo[24]crown-8 ether (20) to form a threaded species. Upon addition of a bulky amine, the aldehyde-terminated template can be converted into an imine in a reversible reaction establishing a dynamic equilibrium (see 29 and 30 in Scheme 17). 

Scheme 16 Synthesis of [3]rotaxane 27 by hydrogen-bonding templated synthesis... 

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