Catenane isomerism

Our definitions of the stereoisomeric center, line, and plane all stipulate the existence of bonds between the ligating element and its ligands. The exclusive use of these elements limits our analysis to classical stereochemistry and thus does not encompass the so-called topological isomerism (47) of interlocked rings—catenanes (48)—or of knots. As there is no bond between the rings of the catenanes we cannot expect to handle such compounds with a system based on connectedness. At the present stage of development, this limitation in scope... 

Supposing this mechanism and considering the restricted circumrotation, the positioning of substituents on the reactants should result in stable isomeric [2]catenanes. Indeed the well-aimed variation of the substitution pattern resulted in three different [2]catenanes - 14-16 (Figures 6 and 7) [20, 21], When isophthaloyl dichloride (3) was reacted with the methoxy-substituted diamine 13 (pathway... 

Figure 6. Variation of the substitution pattern of the reactants (3, 13, 8, and 5) allows the selective synthesis of the isomeric [2]catenanes 14-16.

Figure 7. Mechanism of catenane formation (amide type) the guest is orthogonally embedded in an intermediate macrocycle, the concave template. Depending on the substitution pattern of the reactants (pathways A and B) isomeric catenanes are obtained. For the sake of clarity the diacid dichloride is drawn here to be the nesting guest even though there is clear indication that the effective interactions take place between the corresponding monoamide and the macrocycle.

In contrast, when the substitution pattern is reversed, i.e. the 2,5-fiirane unit is incorporated in the diamine moiety 25 and reacted with isophthaloyl dichloride (3), not only macrocycle 24, but also the two possible isomeric catenanes 26 and 27 are formed. This suggests that the isophthaloyl unit is a better guest or reacts quicker than the furanoyl moiety. The yields obtained for 26 (20%) and 27 (8%) indicate that the isophthaloyl-guest in the second macrocyclization prefers the west-side a) niche of the host 24. Both isomers, the in/out 26 and the out/out 27 furano catenane could be crystallized and their X-ray crystal structures were... 

Figure 17. Synthesis of [2]catenane 45 which is distinguished by a solvent-dependent translational isomerism.

Partial aliphatic catenanes reported by Leigh et al. in 1996 exhibit an interesting solvent-dependent translational isomerism [29]. Stannylation of 43 converts the diol into 44, which is readily soluble in nonpolar solvents (Figure 17). Subsequent treatment with various aliphatic l,co-dicarboxylic acid dichlorides led to catenanes 45 and macrocycles bearing lipophilic chains. 

Figure 7-42. Mass spectrometry allows us to distinguish between isomeric [2+2] macrocycles and catenanes of mass 2M. The mass spectrum of a catenane should show no peaks between m/z 2M and M.

Figure 10.54 Topological isomerism, diastereoisomerism and chirality as related to a [2] catenane, a trefoil knot and a doubly interlocked [2] catenane.

Schill, G., Rissler, K., Fritz, H., Vetter, W., Synthesis, isolation, and identification of translationally isomeric [3]catenanes. Angew. Chem., Int. Ed. Engl. 1981, 20, 187-189. 

For the solvent-dependence of the translational isomerism associated with some catenanes and rotaxanes, see (a) Ashton,... 

Scheme8 Translational isomerism in an amphibilic benzylic amide [2]catenane 16 [55]...

The chemical structures of [2]catenane 19 and the related [3]catenane 20 (Fig. 8) were conceived as an extension of their work on molecular shuttles. The larger macrocycle in 19 comprises two fumaramide stations with differing macro cycle binding affinities. In station B (red) the methyl groups on the fumaramide motif cause it to have lower affinity than the standard fumaramide station. The non-methylated fumaramide station (station A, green) is located next to a benzophenone unit. This allows selective, photosensitized isomerization of station A by irradiation at 350 nm. Station B (red) can be photoisomerized by direct irradiation at 254 nm. The third station, a succinic amide ester (station C, orange), is not photoactive and is intermediate in macrocycle binding affinity between the two fu-... 

The olefin metathesis between alkenyl groups has been frequently used in recent years to stabilize molecules (e.g., dendrimers [46]) or molecular assemblies [47] by additional covalent connectivities [48] and to synthesize macrocydes or more demanding structures like multiple catenanes [24]. Therefore, this reaction was chosen for the connection of alkenyl residues attached to a calix[4]arene via the urea residues. To avoid complications by ds/trans isomerism around the newly formed double bond, the crude reaction mixture was always hydrogenated before working up (Scheme 5.10). 

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>. 

RCM and RORCM reactions in the presence of Grubbs catalysts 151 <1996JA100> and 152 <19990L953> have also been employed for catenane synthesis under reversible thermodynamic conditions. The isomeric ( /Z)-mixture of [2]catenanes 179 was obtained <1998NJC1019> by RCM of an appropriate diimide bearing ethenyl-terminated alkyl chain in the presence of crown ether 170 and catalyst 151. Similarly, initial pseudorotaxane formation followed by metathesis reaction of the double bonds present on the secondary alkylammonium ion axle has afforded [3]catenane 180 as well as [2]catenane 181 <2003TL5773>. 

Interlocking of [2]catenane 182 (( /Z)-mixture) was accomplished by templated RCM of an appropriate acyclic ethenyl precursor as well as RORCM of the two separate constituent rings <20050L2129>. Post assembly hydrogenation was then used to convert the ( /Z)-isomeric mixture of 182 into a single saturated species. 

Figure 5.21 The route-dependent preparation of isomeric catenanes ...

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