Shape catenanes

Like rotaxanes, catenanes are mechanically interlocked molecules. However, instead of interlocking one ring shaped macrocycle and a dumbbell shape, catenanes consist of interlocked macrocycles. The number of macrocycles contained in a catenane is indicated by the numeral that precedes it. Catenanes have bistable and multistable forms and a switchable, bistable [2]catenane is commonly exploited in nanotechnology and molecular electronics because its behavior can be controlled by electrochemical processes [89]. Collier et al. was the first to demonstrate the electroactivity of interlocked catenanes [90]. The authors affixed phospholipid counterions to a monolayer of [2]catenanes and then sandwiched this system between two electrodes. This work resulted in a molecular switching device that opened at a positive potential of 2 V and closed at a negative potential of 2 V. 

Another synthetic strategy is based on self-assembly driven by molecular recognition between complementary TT-donors and 7T-acceptors. Examples include the synthesis of catenanes and rotaxanes that can act as controUable molecular shuttles (6,236). The TT-donors in the shuttles are located in the dumb-beU shaped component of the rotaxane and the 7T-acceptors in the macrocycHc component, or vice versa. The shuttles may be switched by chemical, electrochemical, or photochemical means. 

This molecule has no chiral carbons, nor does it have a rigid shape, but it too has neither a plane nor an alternating axis of symmetry. Compound 32 has been synthesized and has, in fact, been shown to be chiral. Rings containing 50 or more members should be able to exist as knots (33, and see 37 on p. 114 in Chapter 3). Such a knot would be nonsuperimposable on its mirror image. Calixarenes, ° crown ethers, catenanes, and rotaxanes (see p. 113) can also be chiral if suitably substituted. For example, A and B are nonsuperimposable mirror images. 

Pt(en)(N03)2] and [Pt(OTf)2L2] (L = mono- or 1/2 bidentate tertiary phosphine) or dinuclear complexes of the type [Pt2(OTf)2(/i-monodentate tertiary phosphine cr-aryl = 4, -biphenyl, / -terphenyL 4,4 -benzophenone, etc.) other structural motifs employing platinum(II) have also been reported.2 0 The addition of bridging, multidentate N-donor ligands of various shapes and sizes to the labile complexes in a suitable solvent system has afforded several classes of discrete, plat-inum(II)-containing polygons, polyhedra, and catenanes. 

Figure 4. The synthetic strategy for basket-shaped molecules 12 led to a simple one-step synthesis of the tetramethoxy-substituted [2]catenane 11.

When macrocycle 65 is synthesized, the in/out isomer of [2]catenane 79 is also formed in 11% yield (Figure 29) [46]. A first attempt to methylate both sulfonamide groups by treatment of the DMF solution of 79 with iodomethane and potassium carbonate was successful. By bridging the two sulfonamide units with a bifunctional alkylating reagent, we were able to synthesize the first pretzel-shaped molecule [54]. Considerations of the X-ray structure analysis of amide-linked catenanes [16] and CPK models led to the diiodo compound 95 as a suitable brid-... 

The high rigidity of the catenane segments has been demonstrated by a temperature-dependent NMR spectroscopic study of the catenane monomers 44 and 46 [37, 52], Almost no temperature dependence was observed for the line shape of the spectra of the catenane monomers 44 and 46 whereas the temperature had a dramatic influence on the spectra of the unmethylated catenanes 41b,d and 42b,d [30, 37, 52, 56]. Therefore, the poly[2]catenanes 48 and 49 represent one extreme case where there is very little relative mobility of the macrocycles of the catenane segments. 

Numerous metallomacrocycles self-assemble from their components giving species possessing various structures, for instance triangular shape [9.30,9.31] containing a cavity [9.32], which may include a guest molecule [9.33] square [9.34,9.35] or star like [9.36-9.39] shapes wheel-shaped or toroidal hexameric [9.40], octameric [9.41] or decameric [9.42,9.43] structures square [9.44,9.45] rectangular [9.46,9.47] or bent [9.48] boxes into which substrate molecules may bind [9.49,9.50] adaman-tanoid shape [9.51,9.52] with cation inclusion [9.51c], formally related to that of the spheroidal macrotricycle 21 catenane type [9.53]. Coordination species of dendri-mer or arborol nature have been constructed [7.61, 8.27, 9.54]. 

Mechanically connected components of sulfonamide catenanes and rotaxanes can also be connected in an intramolecular manner by linking their sulfonamide moieties and producing the first pretzel-shaped compound 17 [48] and [ljrotaxane 18 [49], respectively. Interestingly, the [l]rotaxane can be bridged intramolecularly giving rise to a molecular 8 compound 19 [50],... 

Yamamoto, C., Okamoto, Y., Schmidt. T., Jager, R., Vogtle, F. Enantiomeric resolution of cycloenantiomeric rotaxane, topologically chiral catenane, and pretzel-shaped molecules observation of pronounced circular dichroism, J. Am. Chem. Soc. 119 (1997), 10547-10548. 

Figure 5.18 Molecular shape of the cyclic [8]catenane 14 (Y = methyl, n= 14) in the crystalline state, showing the interlocking of eight rings. Space-filling representation seen along the Sg-axis (a) and perpendicular to it (b). Alkyl residues and hydrogen atoms are omitted for clarity.

Bauerle and coworkers have synthesized a re-conjugated catenane, utilizing Cu(I) templation and a newly developed method for acetylenic homocoupling based on the reductive elimination of platinum to generate the desired C-C bond formation (Scheme 6.16) [65,66]. The C-shaped 57 was first preorganized around Cu(I), resulting in the homoleptic bis-phenanthroline complex 58. After removal... 

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. 

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