Donor-acceptor catenane

Example 10 Electron donor-acceptor catenanes and rotaxanes... 

The last example is a family of six desymmetrized donor-acceptor catenanes (42+ 92+ Pig 9 4) recentiy investigated [9]. 

When the reaction of two compounds results in a product that contains all the mass of the two compounds, the product is called an addition compound. There are several kinds. In the rest of this chapter, we will discuss addition compounds in which the molecules of the starting materials remain more or less intact and weak bonds hold two or more molecules together. We can divide them into four broad classes electron donor-acceptor complexes, complexes formed by crown ethers and similar compounds, inclusion compounds, and catenanes. 

Stoddart and coworkers [112-115] cyclized bis(bipyridyl)s in the presence of crown ethers to obtain a [2]catenane at a yield of 70%. It is illustrated in Fig. 37. The high yield can be attributed to the 7i-donor-acceptor interaction between the ring and the axle. It was shown that one of the two intercrossed rings moves around the other. The group of Stoddart [116-118] reported [3-5] catenanes (see Fig. 38 for [3]catenane). The [5]catenane of Stoddart et al. [118] was named olympiadane , because it resembles the symbol logo of International Olympic Games, as seen in Fig. 39. 

Ceo-TTF molecules, interlocked molecules (catenanes, rotaxanes), donor-acceptor macrocycles, cage molecules, etc. (Jeppesen et al, 2004). It is beyond the scope of this book to review such developments and I appeal to the curiosity of researchers really not familiar with such macromolecules to see how big the molecules can become. 

In this chapter, for space reasons, only a few paradigmatic examples of rotaxanes and catenanes based on donor-acceptor (charge transfer (CT)) and/or hydrogen bonding interactions (systems based on metal-ligand bonding are reviewed in another... 

As already seen for catenanes 134+ andl44+ (Fig. 13.15),ongoingffomseparated molecular components 16,124+, or 154+ to their catenanes substantial changes in the electrochemical behavior are expected because the electroactive units incorporated in the cyclophanes and macrocycle are engaged in donor-acceptor interactions and occupy spatially different sites. 

The synthesis of polycatenanes requires, like the synthesis of catenanes, the preorientation of the macrocycle precursors into a favorable geometry before cycliza-tion (Scheme 4) [5], This pre-orientation is commonly achieved via a template, resulting from rc-donor-acceptor interactions, hydrogen-bonding, and coordination bonds [1-3, 5, 41], The use of a template in catenane synthesis is the subject of Chapters 4 and 6-8 and will not be treated further in this section. The aim of this section is to present the state of the art of the various synthetic approaches leading to the polycatenane polymers and networks. 

Examples of the incorporation of calixarenes into [2]catenanes are rare. They are not based on the calixarene as such as a macrocycle, but as a fragment for the construction of a eyelobis(paraquat-p-phcnylene) [78,79]. Thus, with bis-p-pheny-lene-[34]crown-10 as the second ring (Figure 5.22a) a [2]catenane is prepared, as described at the beginning of this chapter, using donor-acceptor interactions for the necessary preorganization. 

Scheme 10.10 Formation of 7r-donor/acceptor-tem plated [2]catenanes reported by Sanders and coworkers. 

Sanders and coworkers have used RCM as the final ring-forming step in their neutral donor/acceptor -stacking templated catenanes (64 and 65) with both pyr-omellitimide (66) and naphthodiimide (67) acceptors (Scheme 10.12) [48]. The addition of Lil during synthesis of the pyromellitimide-containing [2]catenane... 

Scheme 10.12 RCM in the synthesis of [2]catenanes using the 7r-donor/acceptor approach by Sanders and coworkers. 

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,... 

Fig. 12 Examples of the use of color in depictions of various types of MIMs. Note how the colors and positions of constituent parts in the three-dimensional structures reflect those in the structural drawings to enhance clarity between representations of (a) a donor-acceptor [2]catenane [75] and (b) an ammonium-binding [2]rotaxane [76] from our group, (c) a transition metal-templated Solomon Knot from the Sauvage and Fujita groups [77], and (d) a benzylic amide [2]catenane from the Leigh group [78]. Reproduced with permission from [75] (copyright 1991 Royal Society of Chemistry), [76] (copyright 2000 Wiley-VCH), [77] (copyright 1999 Royal Society of Chemistry), [78] (copyright 1995 Wiley-VCH)...

Fig. 16 Early examples of MIM cartoons, (a) Sauvage s cartoon of a [3]catenand [101]. (b) Synthetic scheme of a donor-acceptor [2]catenane that uses illustration to emphasize topology, noncovalent bonding, and electronic properties [102]. Reproduced with permission from [101] (copyright 1985 American Chemical Society), [102] (copyright 1991 Wiley-VCH)...

Fig. 18 Different representations of the same donor-acceptor [2]catenane. Line drawings (a) and condensed structural formulas (b) were the order of the day until the modem era of MIMs gave way to structural diagrams (c) and crystal structures (d). Graphical representations, also called cartoons (e), can be a helpful compromise between these representations when attempting to emphasize the topology, noncovalent bonding interactions, shape, beauty, or function of a MIM...

Fig. 27 Examples of thermodynamically controlled reactions employed in the near-quantitative synthesis of MIMs. (a) Disulfide-exchange reaction permits equilibration between a bis(ammo-nium) disulfide dumbbell and a crown ether macrocycle to yield a mixture of [2]- and [3]rotaxanes quantitatively [194], (b) Olefin metathesis at high concentration on a benzylic amide macrocycle greatly favors the catenated species [196]. (c) Self-correcting imine bonds allow for nearly quantitative selection of a [2]rotaxane from an appropriate dynamic combinatorial library [76], (d) A weak nucleophile (E) equilibrates the components of a donor-acceptor [2]catenane in a dynamic Sn2 reaction [205]...

The earliest examples of mechanically bonded molecular switches were two-station rotaxanes and catenanes (a station is a recognition site for the macrocyclic component) that could be switched by these common stimuli. Our group reported a bistable rotaxane in 1994 that could be switched chemically and electrochemi-cally, utilizing a n-n donor/acceptor recognition motif (see Scheme 2 and explanation in corresponding caption) [107]. Many of the recognition motifs in MIMs that... 

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