Salen-based receptor

The salen-based receptor 47 is an example of a selective extractant for metal sulfates. The ligand forms a complex involving deprotonated phenoUc hydroxyl groups and pro-tonated morpholine residues adapted for hydrogen bonding to the anion. The ligand readily extracts CUSO4 into chloroform solution, for example, with essentially 100% efficiency. ... 

A resorcinarene-based receptor functionalized with a Zn-salen complex was tested for the hydrolysis of para-nitrophenyl choline carbonate (Figure 27). The presence of the cavity yielded a fivefold increase of the reaction rate (compared to the corresponding free Zn-salen complex), ascribed to the recognition of the quaternary ammonium knob inside the host by cation-7r interactions. ... 

Reinhoudt and co-workers (236, 237) first reported independently anion receptors (e.g. 122) based on this kind of methodology in 1992. These receptors contained a Lewis acidic neutral uranyl salene group and hydrogen-bonding secondary amide functionalities. Receptors such as 123, containing solely the... 

Other approaches to self-assembling receptors have been reported in recent years. A self-assembling, trimeric palladium complex based on the bis(benzimidazole) ligand (17) was designed by Williams and coworkers [4]. The complex contains a hydrophobic cavity that in the X-ray structure has included a molecule of acetonitrile. In a different context, Schepartz and McDevitt [70] have used the chelation of nickel(n) by A,7V -bis(salicylaldehy-de)ethylenediamine (salen) derivatives to control the position of K -binding glyme chains, and it has been shown that these self-assembled ionophores influence alkali metal transport across liquid membranes [71]. Also, Shinkai and coworkers [72] and Schneider and Ruf [73] have used metal chelation to induce an allosteric effect on binding at a second site. 

We synthesized receptors 26 and 27 which consists of both a uranyl containing salen part for the complexation of the anion and a crown ether or a calix[4]arene tetraester based ionophore for the complexation of the cation [ref 33]. They have been prepared from the corresponding disaldehydes, cw-l,2-diaminocyclohexane and U02(0Ac)2 2H20 in refluxing alcohol. The complexation of the bifunctional receptors with cations and with anions was investigated by NMR spectroscopy, cyclic voltammetry, FAB-spectrometry, and liquid-liquid extraction experiments. 

The Lewis-acidic uranyl dication, UOi, center has been used by Reinhoudt and his group to build up receptors based on uranyl-salen complexes and crown ether units, 12. In particular, the two benzo[15]crown-5 units form a sandwich-like complex with potassium while the metal binds to the dihydrogen phosphate counterion. ... 

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