Cyclobis macrocycle

Four donor acceptor [2]catenanes possessing cyclobis(paraquat-p-phenylene), as the 7i-electron acceptor, and 1,5-dioxynaphthalene-containing macrocyclic polyethers, as the 7i-electron donor moieties, have been constructed employing Cu+-catalyzed Huisgen 1,3-dipolar cycloaddition and Cu+2-mediated Eglinton coupling condition in the final step <07JA8236>. Desymmetrized [2]catenanes were synthesized by means of a template synthesis of pseudorotaxanes between 7i-rich crown ethers and a 7i-deficient pyromellitic subunit,... 

The position of the macrocycle on the thread of a rotaxane can be controlled through repulsive electrostatic interactions generated in a reversible way. Photoin-duced heterolysis of rotaxanes with diaryl-methoxy-cycloheptatriene- and aryl-alk-oxy-acridane-based molecular threads was used in the group of Abraham to demonstrate this concept. Abraham, Grubert, Grummt, and Buck [93] synthesized a rotaxane composed of the tetracationic macrocycle cyclobis(paraquat-p-phenylene) CBPQT (Fig. 9bl) and a thread that incorporated a diaryl-methoxy-cycloheptatriene unit (Fig. 9b2) the thread was folded. In the initial situation (Fig. 9b6), the macrocycle is located at the diary 1-methoxy-cycloheptatriene station (station 1), but due to folding, it interacts also with the aromatic station 2 (for the sake of convenience, the thread in... 

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. 

Aromatic donor-acceptor interactions Stoddart and coworkers discovered that electron-rich fe-p-phenylene-34-crown-lO (25, Figure 14) formed quite a strong complex with the bis(hexafluorophosphate) salt of electron-poor 4,4 -diraethylbipyridinium (26) in acetone and acetonitrile solutions [86]. Conversely, the electron-deficient macrocycle cyclobis(paraquat-p-phenylene) (27) was shown to be an ideal receptor for a wide range of aromatic jc-electron rich substrates such as... 

Recently, electron-transfer catalysis by viologen compounds has attracted much attention. The compounds function as mediators of electron transfer and have been applied in the reduction of aldehydes, ketones, quinines, azobenzene, acrylonitrile, nitroalkenes, etc., with zinc or sodium dithionite in a monophase or a two-liquid phase system [13]. Noguchi et al. [13] found that a redox-active macrocyclic ionene oligomer, cyclobis(paraquat-/ -phenylene), acted as an electron phase-transfer catalyst for the reduction of quinines, as compared with acyclic benzyl viologen. The enhanced activity of this compound is due to the inclusion of the substrate into the catalyst cavity. 

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). 

In 1997, a [2]catenane bearing Cgo was synthesized through Stoddart s methodology,exploiting n-n interactions between aromatic moieties. " The double Bingel addition of a [34]crown-10 bismalonate to Cgo was followed by a ring-closed reaction, where the electron-deficient cyclobis-(paraquat-p-phenylene) (CBPQT +) macrocycle recognizes the electron-rich hydroquinone template. 

As was earlier mentioned, 26-membered macrocyclic carbonate, cyclobis(decamethylene carbonate), was attempted to undergo ROP by lipase catalysis in toluene. Novozym-435 exhibited even higher catalytic activity toward cyclic deca-methylene carbonate dimer polymerization compared with Sn(Oct)2, while high molecular weight (A n) of 54 000 and yield of 99% were still achieved at ultra-low enzyme/substrate (E/S) weight ratio of 1/200. 

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