Cyclobis

Host-guest complexes such as (67) have been prepared from molecular squares involving Lewis base receptor sites, such as cyclobis[(cw-(dppp)Pt(4-ethynylpyridyl)2)(cM-LM)]Ag2 6+(OTf)6, where M = Pdn or Ptn and L = dppp or 2PEt3, by reaction with pyridine, pyrazine, phenazine, or 4,4 -dipyridyl ketone.519... 

Lipase CA catalyzed the polymerization of cyclic dicarbonates, cyclobis (hexamethylene carbonate) and cyclobis(diethylene glycol carbonate) to give the corresponding polycarbonates [105]. The enzymatic copolymerization of cyclobis(diethylene glycol carbonate) with DDL produced a random ester-carbonate copolymer. As to enzymatic synthesis of polycarbonates, reported were polycondensations of 1,3-propanediol divinyl dicarbonate with 1,3-propanediol [110], and of diphenyl carbonate with bisphenol-A [111]. 

Figure 27 illustrates a rotaxane of Stoddart et al. [93], in which the axle contains two stations interacting with the cyclobis(paraquat-p-phenylene) bead. Its NMR spectrum at room temperature indicated that the bead moves back and forth like a shuttle between the stations about 1800 times a second. Stoddart et al. [94,95] prepared a [2]rotaxane containing two bipyridinium units and a crown, as shown in Fig. 28. The shuttling speed of the bead estimated by...

Some authors based their approach to selective binding of the more lipophilic a-amino acids in water on hydrophobic effects using water-soluble, cavity-containing cyclophanes for the inclusion of only the apolar tail under renouncement of any attractive interaction of the hosts with the zwitterionic head . Kaifer and coworkers made use of the strong affinity of Stoddart s cyclobis(paraquat-p-phenylene) tetracation 33 for electron-rich aromatic substrates to achieve exclusive binding of some aromatic a-amino acids (Trp, Tyr) in acidic aqueous solution [48]. Aoyama et al. reported on selectivities of the calix[4]pyrogallolarene 34 with respect to chain length and t-basicity of aliphatic and aromatic amino acids, respectively [49]. Cyclodextrins are likewise water-soluble and provide a lipophilic interior. Tabushi modified )S-cyclodextrin with a 1-pyrrolidinyl and a carboxyphenyl substituent to counterbalance the... 

The versatility and reversibility of exo-active surfaces have been further explored by using pseudo-rotaxane architectures. Pseudo-rotaxanes generated from the electron-deficient cyclophane cyclobi s(paraquat-p-phenylene) (CBPQT4 +) (3) and... 

The [2]rotaxanes, which contain tetrathiafulvalene (TTF) and 1,5-dioxynaphtha-lene (DNP) as the two recognition stations and cyclobis(paraquat-p-phenylene) (CBPQT4 + ) as the cyclic moiety, have been comprehensively investigated by Stoddart and coworkers.68 We have recently reported two new TTF-DNP-CBPQT4+ [2]rotaxanes 62 and 63. In these two [2]rotaxanes, the TTF moiety is the 4,4 (5 )-dialkylthiotetrathiafulvalene that is rather easily accessible based on the synthetic procedure developed by us previously,69 and two different spacers are used the cyclohexyl and alkyl chains. Two stopper units are the G2-dendritic moieties. 

Scheme 5.6 The general principle for the synthesis of catenanes (or rotaxanes) based on cyclobis(paraquat-p-phenylene) and crown ethers containing hydroquinone units. The dipyridyl units are alternatingly stacked with two hydroquinones because of n-n interactions which direct the ring-closure toward the formation of a catenane.

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. 

Similar results have been reported for the host/guest complex formation between a tetracationic cyclophane host [=cyclobis(paraquat-p-phenylene)j and the planar het-eroarene indole. The binding constants Kg, determined in six solvents of different polarities, increase with increasing solvent polarity, being ca. 100-fold greater in water than in acetone [306]. Further examples of solvent-dependent cyclophane/guest complexation reactions can be found in reference [299],... 

The successful syntheses of the above host-guest assemblies pointed the way to the formation of molecular threads - namely, compounds formed by threading a cyclic species, such as the cyclobis(paraquat-/ -phenylene) tetracation, on to a separate extended linear component the product is a pseudorotaxane. Pseudorotaxanes are a derivative category of the rotaxanes in which one of the assembled components is a longer (often oligomeric) linear fragment. They are thus similar to rotaxanes, with the exception that the linear component is not terminated by bulky stoppers . 

A template-directed synthesis of [2]-rotaxanes, with a yield in one case of 72%, has been reported. The experiments employed dumb-bell-shaped components incorporating terminal triisopropylsilyl stoppers connected to a central 1,5-dioxynaph-thalene recognition site by [-CH2CH20-] spacers (n = 1-3). - These components were used as templates for the synthesis ( clipping reaction ) of the corresponding rotaxanes incorporating cyclobis(paraquat-p-phenylene) as the ring component. The... 

Other rotaxanes have been prepared using the slippage strategyOne such example consists of a linear component (terminated by carbohydrate stoppers) that contained a hydroquinone recognition site. This was demonstrated to interact with cyclobis(paraquat-/7-phenylene) tetrachloride in D O over one week at room temperature to yield the corresponding water-soluble catenane. ... 

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

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