Catenanes unsymmetric

A second experiment should prove that macromonocycles are actually the intermediate supramolecular templates in the course of catenane formation. Therefore macromonocycle 17 was reacted with 5 and 3, and the first [2]catenane 18 of the amide type consisting of two different macromonocycles was isolated (Figure 8). Unsymmetric catenanes like 18 can be identified unambiguously by mass spectrometry, because the corresponding tetrameric macromonocycle can not be formed in this reaction sequence. This confirms the presumption that catenation here proceeds via a macrocycle rather than via intertwining open chain units. 

Translational isomerization of a series of [2]catenanes possessing an electron-rich dibenzo-34-crown-10 ether interlocked with rings containing an unsymmetrical 4-substituted resorcinol-based tether linking two electron-poor dipyridinyl groups was demonstrated and studied by VT NMR <07CC4289, 07JOC6454>. 

A related [2]-catenane incorporating the unsymmetrical 1,5-naphtho-/ -pheny-lene-36-crown-10 and the cyclobis(paraquat-/7-phenylene) tetracation has been... 

Fig. 15A-C. Mechanical switching in catenanes. A The individual rings of catenanes may be unsymmetrical. A [2]catenane with two distinct sites on each ring may exist in four different states. B A switchable catenane based on the competitive binding of TTF and dioxynaph-thalene residues on one ring inside the cavity of the second ring. The TTF moiety is bound preferentially in the reduced state, but is repelled in the oxidized state and replaced with the dioxynaphthalene unit. C A proton-switchable [2]catenane. The phenanthroline units in the rings of 37 form a complex around H+, but, when H+ is not present, a charge-transfer complex is formed between the viologen units in one ring and the dioxynaphthalene unit in the other. The absorbance spectra are adapted from [64] with permission...

Liu etal. reported a series of unsymmetrical donor-acceptor [2]catenanes (Figme 44), which could be switched by electrochemical stimuli. Such a feature makes these catenanes appealing candidates for the construction of molecular machines and rotary motors. It should also be noted that these interlocked molecules can be reversibly switched among several states, opening interesting routes for the development of molecular electronic devices that go beyond binary logic. 

Implicit in the preceding paragraphs is the possibility of isomerism in many catenanes of this type. Thus there are four sites in the parent catenane (L1058)(L1072) where p-phenylene may he replaced by m-phenylene [272], These are indicated in Figure 4-13. For the unsymmetrical LI 133, isomeric catenanes are... 

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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