Catenane tetracationic cyclophane component

Figure 13.22 The circumrotation of the tetracationic cyclophane component of catenane 254+ can be controlled reversibly by adding-protonating -hexylamine that forms a charge transfer adduct with the diazapyrenium unit of the catenane.

Figure 13.33 (a) The circumrotation of the tetracationic cyclophane component of catenane... 

Figure 31. Circumrotation of the tetracationic cyclophane component of the [2]catenane 19 + can be controlled reversibly by reducing/oxidizing electrochemically its bipyridinium unit [36a].

Electrochemical techniques can also give interesting information in the case of catenanes of higher complexity, as shown by the results obtained by investigating a series of catenanes made of up to seven interlocked rings.20 The three basic components of these catenanes are the tetracationic cyclophanes 124+ and 154+, and macrocycle 16 containing three electron donor DMN units (Fig. 13.16). For space reasons, only the electrochemical behavior of catenanes 174 1, 188+, 194+, and 204+ (Fig. 13.17), compared to those of their molecular components, is reported. 

This [2]catenane is composed of a jt-electron-deficient tetracationic cyclophane interlocked with a Jt-electron-rich macrocyclic polyether. In addition to a mechanical bond, [jt Jt] stacking interactions between the complementary aromatic units, [C-H---0] hydrogen bonds between the a-bipyridinium hydrogen atoms and the poly-ether oxygen atoms, and [C-H---Jt] interactions between the 1,4-dioxybenzene hydrogen atoms and the p-phenylene spacers in the tetracationic cyclophane hold the two macrocyclic components together and control their relative movements in solution. As a result of the asymmetry of the tetracationic cyclophane, two transla-... 

The macrocyclization reaction described above has been used to generate a great number of catenane (12) and rotaxane (13) architectures (Scheme 10.4) using both crown ethers [preformed macrocyclic components 14 (strategy A)] and hydroqui-none-based dumbbell-shaped polyethers [preformed acyclic components 15 ( clipping )] as templates [14b, 15]. These templates are also relatively robust with regard to the substitution of different groups into both the tetracationic cyclophane and the neutral frameworks. 

Dynamic NMR spectroscopy indicated that the macrocyclic crown component in the [2]-catenane 5 is revolving through the tetracationic cyclophane ring around 300 times per second at 25 °C while it is simultaneously pirouetting around it at about 2000 times per seeond. ... 

A classic example of the formation of a macrocycle by a neutral template is that of the versatile host compound and component of molecular machines, the so-called blue box, or cyclobis paraquat-para-phenylene. Reaction of the horseshoe precursor with dibromo-para-xylene leads to the formation of a tricationic intermediate that is capable of binding the template molecule (Scheme 3), which closes the macrocycle to form the tetracationic cyclophane. The jT-ir interactions of the charge-transfer variety (the complex of the product and template is colored, whereas the components are not) assisted by the charge on ihe product are a major driving force in the process, as revealed in X-ray structures of complexes. It should be noted that the interaction is of the jr-n type assisted by the complementary positive charge on the bipyridinium residues and r-electron-rich nature of the template. This supramolecu-lar synthon can be used for other cyclophanes, catenanes, and rotaxanes (see Self-Assembly of Macromolecular Threaded Systems, Self-Assembled Links Catenanes, and Rotaxanes—Self-Assembled Links, Self-Processes). 

The self-assembly of an optically active [2]catenane involved the incoiporation of a chiral hydrobenzoin unit into one of its component rings one of the p-xylyl groups in the tetracationic cyclophane may be substituted by a flexible CH2CX H2CH20CH2CH2 chain without impeding catenane formation (Scheme 18). However, when both the p-xylyl units are replaced, the tetracationic cyclophane loses its ability to complex with Tc-electron rich aromatic substrates. This achievement has implications for the design of chiral solid-state devices and the construction of asymmetric catalysts. 

Bisfunctionalized [2]catenanes have been also prepared by employing template-directed syntheses that involve the interaction of 7t-donors and Jt-acceptors. Reaction (Fig. 10) of the dibromide 31 with the dicationic salt 32 in the presence of either 33 or 34 as the macrocyclic polyether component afforded [105] the [2]catenanes 35 and 36, respectively, after counterion exchange. The aromatic hydroxymethyl group located within the tetracationic cyclophane portion of the [2]catenane 35 was converted [106] into a chloromethyl group by treatment of 35 with 10 M HClaq. After counterion exchange, the chloromethyl group was... 

It is obvious that we can only self-assemble [3]catenanes if we increase the size of both the neutral and tetracationic components. So far, the use of TPP68C20 and the large cyclophane [BBIPYBIBTCY]4+ has met with no success. We attribute this lack of catenation to the large dimensions of the two components, and, in the case of TPP68C20, to its flexibility. The macrocyclic polyether TPP51C15 Scheme 21),... 

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