Catenanes translational isomers

Figure 17. The degenerate forms A and B of the [2]catenanes 32-4PF6-38-4PF6 and the translational isomers A and B of the [2]catenanes 394PF6-48-4PF6.

Scheme 9 Chemically and electrochemically driven translational isomer switching of [2] catenane 17 [56]...

The [2]catenanes 185 and 186 incorporated different 7t-electron-rich macrocyclic components. As a result, their H NMR spectra showed the existence of two translational isomers in solution as shown in Scheme 28. The ratios between the two translational isomers A and B of [2]catenanes 185 (by 181 -[cyclobis(para( uat-/)-xylylene)][PF,3]4) and 186 (by 182-[cyclobis(paraquat-p-xylylene)][PF6]4) are 60 40 and 70 30 at — 30°C, respectively. Increasing the temperature up to +30 °C resulted in an increase of the population of the translational isomers B in 185 and 186 to 55 45 and 30 70, respectively. A temperature dependence of the equilibrium between the translational isomers associated with 185 and 186 was observed. These [2]catenanes can be regarded as temperature-responsive molecular switches. 

Scheme 28 Translational isomers associated with the [2]catenanes 185 and 186.

In an attempt to improve control over the relative amounts of translational isomers formed, systems in which the binding abilities of both the 7C-donor and 7C-acceptor units were varied have been synthesised. One example is the [2]-catenane 13 in which all four building blocks are different. Since this catenane incorporates four different 7C-systems, four different transitional isomers are possible. However, in... 

In the case of the previously discussed [2]catenane 18 + shown in Figure 30, switching from the more stable translational isomer (which contains a TTF unit inside the tetracationic cyclophane) to a less stable one can be obtained not only by oxidation of the TTF unit, but also by addition of o-chloroanil. H NMR spectroscopy shows that o-chloroanil gives an adduct, presumably CT in nature, with the TTF unit which locks this unit alongside the cavity of the cyclophane. On addition of Na2S205 the adduct is destroyed and the original isomer with the TTF unit inside the cavity of the cyclophane is restored [59, 66[. 

In principle, the control of translational isomerism may be accomplished by steric and/or electronic means. We chose the macrocyclic polyether 1/5NPP36C10, containing one hydroquinol ring and one 1,5-dioxynaphthalene ring system, in order to investigate the influence of steric and electronic factors on the positon of the equilibrium between two translational isomers. It was expected that, if this crown ether could be incorporated into a [2]catenane, then the difference in both the size and the tc-donating ability (naphtho > benzo) of the two units would strongly influence the relative populations of the translational isomers in solution. 

Table 2. The difference in population of translational isomers in the [2]catenanes containing unsymmetrical tetracationic cyclophanes at low temperature (<240 K) in CD3COCD3. Refer to Scheme 17.

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