Templated catenane synthesis

Sauvage, J.-P. Dietrich-Buchecker, C. O. Chambron, J.-C. Transition metals as assembling and templating species synthesis of catenanes and molecular knots. In Comprehensive Supramolecular Chemistry, Sauvage, J.-P. Hosseini, M.W., Ed., Publisher Elsevier, Oxford, UK 1996 Vol. 2, p 43. 

As already said, catenanes are minimally composed of two interlocked rings. If it is arranged during the template-directed synthesis to have two identical units, that is, recognition sites, located within two different macrocycles, then the resulting... 

Figure 15. The template-directed synthesis of the [2]catenanes 32-4PF6-384PF6. The insets show (i) the intermediate [2]pseudorotaxane formed during the course of catenane formation and (ii) the solid-state structure of the [2]catenane 324+.

Figure 28. The hydrogen-bonding template-directed synthesis of the [2]catenane 87.

The synthesis of polycatenanes requires, like the synthesis of catenanes, the preorientation of the macrocycle precursors into a favorable geometry before cycliza-tion (Scheme 4) [5], This pre-orientation is commonly achieved via a template, resulting from rc-donor-acceptor interactions, hydrogen-bonding, and coordination bonds [1-3, 5, 41], The use of a template in catenane synthesis is the subject of Chapters 4 and 6-8 and will not be treated further in this section. The aim of this section is to present the state of the art of the various synthetic approaches leading to the polycatenane polymers and networks. 

Although structurally and functionally appealing, the synthetic ways to build these species remained a hard task until mid 80s. Then, a strategy was developed by Sauvage and his co-workers that used coordination to a Cu(I) ion prior to the macrocyclization in the catenane synthesis (Figure la). The metal that served as a template with tetrahedral coordination geometry was then removed by demetallation with cyanide [8],... 

Raymo, F.M., Stoddart, J.F. Organic Template Directed Synthesis of Catenanes, Rotaxanes and Knots. In ref. 4b, p.143. 

Fortunately, more efficient methods for the complexation of macrocyclic hosts with acyclic guest molecules have become available with the advent of supramo-lecular chemistry, resulting in higher yields in rotaxane and catenane synthesis. In the following sections, the preparation of different types of interlocked molecules, with the use of host-guest recognition, is discussed. It should be noted that these template-directed methods differ significantly from the above-mentioned stochastic approach [28]. 

Sanders and coworkers have used RCM as the final ring-forming step in their neutral donor/acceptor -stacking templated catenanes (64 and 65) with both pyr-omellitimide (66) and naphthodiimide (67) acceptors (Scheme 10.12) [48]. The addition of Lil during synthesis of the pyromellitimide-containing [2]catenane... 

For accounts and reviews on the use of this recognition motif to template the synthesis of catenanes and rotaxanes, see (a) Amabilino, D. B. and Stoddart,... 

The -electron-deficient pyridinium ring has played an important role in template-directed synthesis in which the interaction of a -electron acceptor and a -electron donor facilitate self-assembly. This has led to the construction of a variety of supramolecular assemblies including catenanes (linked rings) and rotaxanes (wheel and axle) . 

Fig. 8 The two applied approaches to catenane synthesis prior to 1983. (a) The first statistical synthesis [58] relied upon the macrocyclization of a linear compound (7) in the presence of a deuterated cycloalkane (III) to achieve small amounts of the catenane V. (b) The first example [59] of directed synthesis by covalent templation was a catenane that formed after cleaving the covalent bonds around the aromatic core in compound 16. Reproduced with permission from [58] (copyright 1960 American Chemical Society), [59] (copyright 1964 Wiley-VCH)...

In 1989, following extensive preparatory work discussed, the template-directed synthesis of the positively charged [2]-catenane 5 was reported by the Stoddart group (Figure 5.2). Only mild conditions were required, with the crystalline catenane... 

Figure 5.17 The multistep template-directed synthesis of the high-order catenanes...

Stoddart and co-workers transferred the strategy of template-directed synthesis to the formation of the first molecular system consisting of five interlocked rings in a linear array (Structure 51). They suggested that this [5]catenane should be called olympiadane [64]. Recently they reported the self-assembly of a new type of rotaxane, in which three side chains are linked directly to a single central core, producing a dendritic-type structure [65]. 

The very first rotaxanes were, however, not prepared via the template technique. In 1967, Schill and Zollenkopf [3] described a directed rotaxane synthesis (i.e. by the use of temporary, cleverly disposed covalent bonds), which was traced from the first directed catenane synthesis developed by Schill and Luttringhaus in 1964 [32]. Quite simultaneously, Harrison and Harrison published the first rotaxane synthesis by statistical threading [4]. 

The breakthrough in catenane synthesis occurred when the statistical and covalent template methods were abandoned in favor of approaches that relied... 

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