Catenanes structure

Increasing the length of the alkyl spacer in such a way as to yield 1,4-bis(tetrazol-l-yl)butane (abbreviated as btzb) (Fig. 16), changes the dimensionality of the Fe(II) spin crossover material [89]. In fact, [Fe(btzb)3] (C104)2 is the first highly thermochromic Fe(II) spin crossover material with a supramolecular catenane structure consisting of three interlocked 3-D networks [89]. Unfortunately, only a tentative model of the 3-D structure of [Fe(btzb)3](Cl04)2 could be determined based on the x-ray data collected at 150 K (Fig. 20). 

In a catenane, structural changes caused by dr-cumrotation of one ring with respect to the other can be clearly evidenced when one of the two rings contains two non-equivalent units. In the catenane shown in Figure 8,1261 the ring containing the electron-acceptor units is symmetric , whereas the other ring is non-symmetric since it contains two different electron-donor units, namely, a tetrathia-... 

Week M, Mohr B, Sauvage J-P, Grubbs RH. Synthesis of catenane structures via ring-closing metathesis. J Org Chem 1999 64 5463 -5471. 

As discussed in Section 13.2.4, when one of the two rings of a catenane carries two different recognition sites, the dynamic processes of one ring with respect to the other can be controlled. In particular, if redox units are incorporated into the catenane structure, there is the possibility of controlling these processes upon electrochemical stimulation. Catenanes that exhibit such a behavior can be seen as electrochemically driven molecular rotors. An example is offered by catenane 384+ (Fig. 13.33a), which incorporates macrocycle 2 and a tetracationic cyclophane comprising one bipyridi-nium and one trans-l,2-bis(4-pyridinium)ethylene unit.19,40... 

Scheme 14. Catenane isomers 40-42. The rings bearing the substituents OUT (IN) of the catenane structure are referred to as OUT (IN) rings, respectively.

With the exception of DNA catenanes and protein catenanes, and despite various synthetic attempts, only one polymeric catenane structure, i.e. the catenated block copolymer 72, is known [31]. Evidently, the fact that the two constitutive cyclic polymers have two different chemical structures greatly facilitates the syn-... 

Figure 23 Representation of the structure of an open chain Cu1 chelate,13 with two phen ligands arranged in a distorted tetrahedron around Cu1. Subsequent ring closure results in a very interesting catenane structure...

Catenanes and Molecular Capsule - Complex Molecular Associations Interlocking several rings results in a catenane structure. Catenanes can be obtained efficiently using supramolecular concepts. The spontaneous formation of a palladiiun coordination complex is an elegant process that is used in the synthesis of catenanes and molecular capsules. 

Supramolecular interactions are an important factor in catenane formation. Such interactions can be disrupted after the catenane has been built, making the catenane structure more flexible. This flexible nature can be an advantage because the catenane structure is then free to respond when external stimuli are applied. The catenane shown in Fig. 3.26 is one example where this structural flexibility is utilized. One of the rings of this catenane contains two kinds of ligands, and the nature of the coordination to the copper ion depends on the oxidation number of the copper. When the copper ion is in the Cu(I) state, fourway coordination is stabilized. However, five-way coordination becomes more favorable upon oxidation to Cu(II), and to accommodate this, the ring rotates... 

Catenane synthesis can be also achieved by dynamic molecular association. Figure 3.27 shows an example of catenane preparation through the dynamic formation of a palladium (Pd) complex. Mixing the Pd complex with pyridine-type ligands in water induces the formation of both a monocyclic structure and an interlocked catenane. An equilibrium exists between these two structures, and the catenane structures are more favorable at higher concentrations. In the catenane structure, the benzene rings stack next to each other due to favorable... 

Often in this book we refer to selectivity as the most burning problem of organic synthesis and mentioned that complexation may be employed as an efficient tool to deal with this problem. This same principle was successfully applied to the elaboration of the directed synthesis of catenane structures. 

In macrocycle 10, the three donor units undergo distinct oxidation processes, indicating that there are electronic interactions between oxidized and nonoxidized units. As a consequence of the CT interaction with the electron-acceptor cyclophane, in the catenane 11" + all these processes move to more positive potential values with respect to the free macrocycle. A detailed comparison between the two oxidation patterns is made difficult because, in the catenane structure, the donor-acceptor interactions between nonoxidized and oxidized donor units are partially or completely prevented. In the [3]catenane 12 +, only two oxidation processes are observed, a feature which is consistent with the presence of an outside and two equivalent inside donor units. 

The only example presently available of photochemically controllable ring motion through an electron transfer reaction in a catenane structure concerns a Cu+-based [2]catenate, which is discussed in Volume 111, Part 2, Chapter 8 [64], Examples of catenanes containing cis-trans photoisomerizable units and where ring motions can be photochemically controlled are also known [65]. 

Recently Vogtle and co-workers synthesized the first catenanes (Structure 53) and rotaxanes containing sulfonamide units. The sulfonamide catenanes 53a, 53b have a topologically chiral structure [67]. 

Physical properties of these poly[2] catenaries have been explored in expectation of unique properties based on the catenane structure [239, 246]. While various interesting physical properties were found in polyrotaxane, no characteristic property has been reported in [2]catenanes so far. Although poly[2]catenane has highly mobile moiety due to the mechanical bond, it has been suggested that the connection between [2]catenane subunit restricted the mobility in motion of [2]catenane. Further, intramolecular interaction in [2]catenane subunit may decrease its mobility. Secondary amide-based [2]catenanes can easily be prepared from commercially available compounds. Takata et al. found that the borane-reduction of the [2]catenanes afforded good yields of the amine-based [2]catenanes that can be useful for polymer synthesis [247, 148] (Scheme 51). Although the origi-... 

Many researchers have tried to prepare poly[n] catenane. However, all attempts have so far been unsuccessful. The first proposal for the preparation of poly[n]catenane was illustrated in the early 1970s [262-265]. Hydrocarbon terminated by hydrophilic functional groups was spread on the organic solvent-water interface. It was claimed that connection of the resulting U-shaped molecules by appropriate cyclic compounds followed by ring-closure afforded poly[n] catenane. However, no direct evidence for the poly[n] catenane structure was reported. A more sophisticated proposal based on the... 

Figure 11. Examples of peculiar rotaxane and catenane structures (a) a branched [4]rotaxane [50], (b) a [5]catenane named olympiadane [52], (c) a rotacatenane [54], and (d) a [2]catenane composed of three macrocyclic rings [53],...

Figure 18. In [2]catenane 20 + [86], upon excitation of its [Rutbpy), p moiety, a very fast electron transfer process to a bipyridinium unit occurs. Owing to the catenane structure, the two bipyridinium units do not possess the same reduction potential (half-wave potential values versus SCE for the inside and outside units are indicated) such a redox asymmetry could mimic that of the cofactors in the bacterial photosynthetic reaction center.

This strategy has been further extended to the synthesis of a triply twisted tris[bis(phenanthroline)copper(I)] complex analogous to (35) which, after correct linking of the termini and demetalation, leads to a doubly interlocked catenane structure [46]. 

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