Convergent hydrogen bonds

Figure 1. Urea and 2-amidopyrrole provide parallel and convergent hydrogen bond donation respectively.

Figure 39. Hangman salens with convergent hydrogen-bonding clefts.

Gale and co-workers have developed a number of receptors based on the 2,5-dicarboxamidopyrrole skeleton where the combination of a pyrrole and amide groups form convergent hydrogen-bonding arrays (e.g. 37a and 37b) [50]. 

Choi, K. Hamilton, A.D. Selective anion binding by a macrocycle wdth convergent hydrogen bonding functionality. J. Am. Chem. Soc. 2001. 123 (10), 2456-2457. 

Alcazar. V. Segura. M. Prados, P. de Mendoza, J. A preorganized macrocycle based on a bicyclic guanidinium subunit with six convergent hydrogen bonds for anion recognition. Tetrahedron Lett. 1998. 39 (9). 1033-1036. 

Figure 19 Minimized model (molecular mechanics) for complementary ft-It stacking and convergent hydrogen bonding between the pyrenylurea end-group of 11 and a bis(diimide) chain-fold of 9. (Reproduced with permission from Ref. 36. American Chemical Society, 2010.)...

Co-ordination chemistry is not the only possible approach to the successful preparation of supramolecular dendrimers. Other examples include hydrogen-bonded dendrimers, which have been prepared using tetracar-boxylic acid moieties as the linking species, and others have been prepared where the hydrogen bonds were developed using melamine and cyanuric acid at the focal point (i.e. the point towards which convergent synthesis is directed). 

We have now adjusted our molecular systems to provide a model in which both forces can operate simultaneously. The U-shaped relationship that exists between the imide function and amides of aryl amines creates a hydrogen bonding edge and a planar stacking surface that converge from perpendicular directions as in 44 to provide a microenvironment complementary to nucleic acid components. A large number of aromatic rings can be functionalized with this simple scaffold, and spacers (R) can also be incorporated. The imide function is a mimic of the thymine residues. 

Another series of macrocycles prepared by hydrogen bonding to anion templates are the [ljimidazoliophanes recently reported by Alcalde [27]. The preparation of such macrocycles is based on a 3+1 convergent maerocyclization reaction which is highly dependent on the presence of specific anions (see Scheme 4). The yields of this reaction vary between 42%, when no anion is pre-... 

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