Catenanes hydrogen-bonded

Once again, pyridines are often used as simply rigid structural components in catenanes. Hydrogen bonding may limit the extent of rotation in such systems, as is demonstrated in the homocircuit catenane 102 <1998JA6458>. 

Schalley CA, WeUandt T, Briiggemann J,V6gtle F (2004) Hydrogen-Bond-Mediated Template Synthesis of Rotaxanes, Catenanes, and Knotanes. 248 141-200 Scheer M,see Balazs G (2003) 232 1-23... 

Figure B. Pictorial representation of the self-assembly of pseudorotaxa-nes based on (a) charge-transfer and C-H—O hydrogen-bonding interactions between 1,1 -diben-zyl-4,4 -bipyridinium dication and 1,5-dinaphtho[38] crown-10 (1/5DN38C10), and (b) hydrogen-bonding interactions between dibenzyl ammonium ion and dibenzo[24]crown-8 (DB24C8). A possible route towards the synthesis of rotaxanes and catenanes is also schematized.

Keywords Templates Hydrogen Bonding Self-assembly Cages Macrocycles Catenanes ... 

In the early 1990s Hunter [49] and Vogtle [50,51] discovered independently the possibility of using hydrogen bonding interactions displayed by amide groups to template the formation of [2 ] catenanes. While studying the reaction between the... 

Scheme 9 Hydrogen bonding interactions are responsible for the appropriate orientation of the components that lead to the formation of catenanes 12 and 14... 

Scheme 10 Leigh has reported the hydrogen-bonding templated synthesis of catenane 15...

Each catenane consists of two identical, interlocked 26-membered rings with a relatively small internal cavity (with dimensions of 4x6 A). This interlocked species was the first amide-catenane to be structurally characterised (although Hunter s and Vogtle s catenanes were reported earlier). The structure supported the proposal that the driving force for catenane formation is hydrogen bonding between the newly formed 1,3-diamine units and carbonyl groups of the acid... 

Scheme 11 Hydrogen-bonding templated preparation of catenane 18 under thermodynamic control...

This elegant synthesis has demonstrated the possibility of using a hydrogen bond-acceptor template to prepare template-free interlocked species (in a similar fashion to Sauvage s catenanes syntheses which make use of transition metals as templates). 

Houk, Stoddart and Williams have carried out a detailed investigation (involving experimental and theoretical studies) to quantify the strength of C-H- -O hydrogen bonds in the formation of catenanes [82]. While the formation of the [3]catenane 67 was successful, its conversion to the [4]catenane 68 could not be achieved (see Scheme 32). 

Schalley CA, Weilandt T, Briiggemann J, Vogtle F (2004) Hydrogen-bond-mediated template synthesis of rotaxanes, catenanes, and knotanes. Top Curr Chem 248 141-200... 

Hydrogen-Bond-Mediated Template Synthesis of Rotaxanes, Catenanes, and Knotanes... 

Hydrogen bonding is thought to be responsible for the formation of such molecules as the catenane 37 [17], rotaxane 396 [18] and even knot 397 [19]. 

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... 

It should be noted that, more recently, two different, also highly efficient template catenane syntheses have been developed one of them, first introduced by Stoddart and coworkers [70], is based on the n donor-7t acceptor gathering effect between aromatic nuclei, whereas in the second, mainly developed by Hunter and Vogtle and coworkers, gathering and orientation of the various subunits of the future catenane are induced by hydrogen bonding [71-73]. 

Figure 26. The hydrogen-bonding template-directed syntheses of the [2]catenanes 78 and 80.

Catenane 7 exists in a well defined conformation in which two identical macro-cycles are interlocked and held together by six hydrogen-bonds. The crystal structure also revealed the chirality of the ground state conformation. 

The [2]catenane syntheses presented so far are very sensitive towards modification of the building blocks, e.g. no [2]catenane can be detected when nitro-substi-tuted isophthaloyl dichloride is reacted with diamine 4 [8 a]. The NO2 group seems to disturb the template by competing with the carbonyl groups in forming hydrogen-bonds with the NH groups. 

The tetramer exhibits an interesting folded conformation (in contrast to the open conformation of 6) which enables the binding of two p-benzoquinone molecules. Intramolecular hydrogen bonds between the nitrogen lone pair and the amide protons force the 2,6-pyridyl moiety into a NH cis conformation which consequently leads to the observed folded structure (Figure 10). In contrast to this, the open conformation of 6 enables the isophthaloyl unit to adopt the usually energetically favored NH trans conformation to optimize the amide-amide interactions. Because of the folded structure of tetramer 21 a tetramer-dimer catenane 22 could be isolated in 29% yield and even traces of the corresponding [3]cate-nane were detected. 

NMR studies showed that in polar solvents (DMSO, DMF) catenane 45 adopts a supramolecular conformation (II) that allows the amide protons to interact via multiple hydrogen bonds with solvent molecules and at the same time buries the lipophilic chains in the center of the molecule (Figure 18). In contrast, NMR spectra in nonpolar solvents indicate that the aliphatic chains are situated on the outer sphere of the catenane, whereas the isophthaloyl units are arranged in a way that ensures optimal intramolecular hydrogen-bonding (I). 

This conformation resembles that determined by X-ray single-crystal structure analysis. Apart from a close interaction of the -system of the amide groups with the para-substituted aryl moieties, no further n-n interactions are observed. The template-assisted catenane formation is on this account mainly driven by hydrogen-bonding, and n-n interactions are of minor importance only. 

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