Cyclophanes binding

Figure 11.5 Crown ether cyclophane binds squaraine dye only in the presence of sodium cations...

An example of the modular preparation of the cyclophane 3 from the substituted bipyridine 2 and a general tripeptide 1 is shown in Scheme 3-3. The host molecule 3 contains a pre-organized binding pocket. The overall basicity of such molecules also facilitates their intercalation within the lamellas of acidic zirconium phosphate, thus making this chemistry well suited for the desired application. 

With these features in mind, we envisioned a new family of macrocyclic ligands for olefin polymerization catalysis (Fig. 9) [131, 132], We utilized macrocycles as the ligand framework and installed the catalytic metal center in the core of the macrocycles. Appropriate intra-annular binding sites are introduced into cyclophane framework that not only match the coordination geometry of a chosen metal but also provide the appropriate electronic donation to metal center. The cyclophane framework would provide a microenvironment to shield the catalytic center from all angles, but leaving two cis coordination sites open in the front one for monomer coordination and the other for the growing polymer chain. This could potentially protect the catalytic center and prevent it from decomposition or vulnerable side reactions. 

The first is a cyclophane-based system reported by Murakami et al. (Fig. 9.12a). [31] The sides of the host consist of tetraaza-[3.3.3.3]paracyclophane units, and its octaprotonated cation has been shown to bind anionic guests. The molecule possesses 48 asymmetric units of [(N/3)-(CH2)- (C6H4)/2 ]/2. 

The apparent binding constant K y obtained by Stern-Volmer quenching studies is the product of the number of receptors visited by the exciton and the binding constant of to the cyclophane receptor. For this reason polymer 3 and its monoreceptor model 2 were designed so that the binding constant for methyl viologen to the receptor was known for both systems. This allowed the calculation of the true amplification factor of 67. 

Habicher T, Diederich F, Gramlich V. Catalytic dendrophanes as enz3mie mittfics. Synthesis, binding properties, micropolarity effect, and catal3ftic activity of dendritic thiazolio-cyclophanes. Helv Chim Acta 1999 82 1066-1095. 

Cyclophanes must have the appropriate binding sites at least 3-4 A shorter in diameter. 

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