Bis -cyclophane

Whereas the identification of a [1 + 1] or a [2 + 2] cyclization product was unequivocal by MS, it was more difficult to distinguish between the concave bimacrocycles and the bis-cyclophanes. But a combination of NOE investigations with complexation studies followed by NMR, and finally X-ray analyses proved the bimacrocyclic concave structure of the concave acids and bases 21,29 and 38 [15, 20, 27a]. 

A bis(cyclophane)ruthenium(II) complex has been prepared by using Bennett s procedure reaction of diene 265, obtained by Birch reduction of 4,5,7,8-tetramethyl[22](l,4)cyclophane 266, with ruthenium chloride gives the dimeric chloride complex 267 (Scheme 27, p. 223). Treatment of the solvated complex 268 with 266 in the presence of trifluoroacetic acid leads to 269 (163). The structures of complexes 267, 268, and 269 are based on ... 

A more general route to make bis(cyclophane)ruthenium(II) complexes involves a reduction of 263 (arene = benzene) with Red-Al to afford the [ 174-1,3-cyclohexadiene)(tf-cyclophane)]ruthenium(O) derivatives 271 (Scheme 28, p. 224). Treatment of 271 with hydrochloric acid gives the dimeric chloride complexes 272, which lead the desired bis(r)6-[2 ]cyclo-phane)ruthenium(II) complexes 274 via Bennett s procedure (145). Synthesis of the oligomer 275a is also achieved in quantitative yield by heating 274 with the solvated complex 7 (arene = C6Me6) in neat trifluoroacetic acid. 

The linkage of two meta-cyclophanes by alkyne groups gave bis-cyclophane 106. Extraction experiments revealed a moderate binding of purine- and pyrimidine by these molecular tweezers [65]. The preferred conformation of [2.2]-metacyclophanes is the azzfz -arrangement [66]. Bodwell et al. [67] showed now that a 13-membered bridge levels the energy of syn- and anfz-conformer of 107. They slowly interconvert in solution at room temperature. 

Bis-cyclophanes (26) having two independent binding sites, capable of forming complexes at two sites, were synthesized by connecting two cyclophane units [11]. 

When Illb is heated with p-phenylenediamine at 200-300°C under conditions similar to the other phenylenediamines, mainly insoluble, probably crosslinked, oligomers (rubber-like solid) are formed. On the other hand, p-phenylenediamine with bis(diethylamino)dimethylsilane at 180°C yielded a toluene-soluble solid whose molecular weight and elemental analysis agree well with the probable cyclophane structure IX for C32H48NsSi4 Mcaic. 657.16, found Mcryoscopic 648, m/e 657.16 calc. % C, 58.49 H, 7.36 N, 17.05 Si, 17.10 found % C, 58.40 H, 7.42 N, 17.10 Si, 17.16. The structure of this compound is being further investigated. 

Several silver(I) complexes of the macrocyclic Schiff base derived from the [2+2] condensation of terephthalaldehyde and 3-azapentane-1,5-diamine or A,A -bis(3-aminopropyl)methylamine have been described.509,510 The reaction of 2,ll-diaza-difluoro-m-[3,3]-cyclophane with 2,6-bis (bromomethyl)pyridine lead to the 3 + 3 addition product, which gives a complex with two silver... 

Among the cyclophanes 12, 17, and 22, the absorption band of 22 appears at the longest position. However, the bathochromic shifts in these cyclophanes should be compared with the corresponding acyclic compounds l,4-bis(pentamethyldisilanyl)benzene 23, l,4-bis(penta-methyldigermanyl)benzene 24, and l,4-bis(pentaisopropyldistanna-nyl)benzene 25 (Fig. 13). 

Macrocycles containing isoxazoline or isoxazole ring systems, potential receptors in host—guest chemistry, have been prepared by multiple (double, triple or quadruple) 1,3-dipolar cycloadditions of nitrile oxides, (prepared in situ from hydroxamoyl chlorides) to bifunctional calixarenes, ethylene glycols, or silanes containing unsaturated ester or alkene moieties (453). This one-pot synthetic method has been readily extended to the preparation of different types of macrocycles such as cyclophanes, bis-calix[4]arenes and sila-macrocycles. The ring size of macrocycles can be controlled by appropriate choices of the nitrile oxide precursors and the bifunctional dipolarophiles. Multiple cycloadditive macrocy-clization is a potentially useful method for the synthesis of macrocycles. 

During the synthesis of [2.2]paracyclophanediene, Dewhirst and Cram 83> prepared the bis-geminal dibromides 4a and 4b, which were subsequently converted into the diketones 5 a and 5 b. The UV spectra of the bromides 4a and 4 b show maxima at 236 nm. A comparison with the Amax values of other [2.2]paracyclophanes brominated at the bridges suggests that the absorption at 236 nm is the 235 nm band of [2.2]para-cyclophane, shifted bathochromically by the inductive effect of the... 

Among the three isomers of bis(phenylmethylenyl) [2.2]paracyclophanes [38], pseudo-ort/jo- and pseudo-para-isomers (o-[38j and p-[38], respectively) satisfy McConnell s condition to give quintet ground states. They were produced by photolysis of the corresponding bis(a-diazobenzyl)[2.2]para-cyclophanes [38a] in 2-MTHF at cryogenic temperatures, and their esr fine structures were studied. 

In the synthesis of concave 1,10-phenanthroline cyclophanes 21 (Scheme 4), the aryl bridgeheads could be easily introduced by the addition of two aryl lithium moieties 16 to 1,10-phenanthroline (15). Although aryl lithium compounds may also be added to pyridine [23], this approach could not be realized for the construction of concave pyridine cyclophanes 29 yet [24]. Therefore another route for the synthesis of the concave pyridines 29 was used (Scheme 5) the cyclization of 1,5-diaryl substituted Cj-units 23 or 27 with ammonia. The resulting 2,6-bis(2,6-dimethoxyphenyl)pyridine 24 [25], the pyridine analogue to the tetramethoxy-1,10-phenanthroline derivative 17, was then treated in the same way. After liberation of the phenol functions, the four OH groups of 28 were reacted with two equivalents of diiodides 19 [25]. As in the synthesis of the concave 1,10-phenanthroline cyclophanes 21, two macrocycles were formed in one reaction step. 

As discussed in Section 13.2.4, when one of the two rings of a catenane carries two different recognition sites, the dynamic processes of one ring with respect to the other can be controlled. In particular, if redox units are incorporated into the catenane structure, there is the possibility of controlling these processes upon electrochemical stimulation. Catenanes that exhibit such a behavior can be seen as electrochemically driven molecular rotors. An example is offered by catenane 384+ (Fig. 13.33a), which incorporates macrocycle 2 and a tetracationic cyclophane comprising one bipyridi-nium and one trans-l,2-bis(4-pyridinium)ethylene unit.19,40... 

In the major isomer, the bipyridinium unit is located inside the cavity of the macrocyclic poly ether and the /7Y//7,v-bis(pyridinium)ethylene unit is positioned alongside, as confirmed by the electrochemical analysis. The cyclic voltammo-gram of the catenane shows four monoelectronic processes that, by a comparison with the data obtained for the free cyclophane, can be attributed as follows the first and third processes to the first and second reductions of the bipyridinium unit, and the second and fourth ones to the first and second reductions of the trans-bis (pyridinium)ethylene unit. The comparison with the tetracationic cyclophane also evidences that all these reductions are shifted toward more negative potential values (Fig. 13.33b). 

The discussion can be restricted to the first and second reduction processes that are of particular interest in this context. The shift of the bipyridinium-based process is in agreement with the catenane coconformation in which the bipyridinium unit is located inside the cavity of the macrocyclic polyether (Fig. 13.33a) because of the CT interactions established with both the electron donor units of the macrocycle, its reduction is more difficult than in the free tetracationic cyclophane. The shift of the trans-1,2-bis(4-pyridinium)ethylene-based reduction indicates that, once the bipyridinium unit is reduced, the CT interaction that stabilize the initial coconformation are destroyed and, thereby, the tetracationic cyclophane circumrotates through the cavity of the macrocyclic polyether moving the tra ,v-bis(pyridinium)ethylene unit inside, as shown by comparison of its reduction potential with that of a catenane model compound.19 The original equilibrium between the two coconformations associated with catenane 384+ is restored upon oxidation of both units back to their dicationic states. 

Bis-chlorophylls (134)515 517 and cyclophane -chlorophylls (135)518 are reported to exhibit several photochemical properties which mimic the in vivo special pair chlorophylls. By... 

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