Molecular Receptors for Adenine and Guanine Employing Metal Coordination, Hydrogen‐Bonding and π‐Stacking Interactions
- 1 August 1997
- journal article
- research article
- Published by Wiley in Chemistry – A European Journal
- Vol. 3 (8) , 1203-1213
- https://doi.org/10.1002/chem.19970030807
Abstract
Thiacyclophane ligands 1 and 2, containing a meta‐xylyldithiaether unit, an aromatic spacing unit and a polyether chain, were prepared in good yield in a three‐step synthesis. The macrocyclic organopalladium complexes [Pd(L)‐(MeCN)][BF4] (3: L = 1; 4: L = 2) were prepared through palladation of the respective thiacyclophane ligand by reaction with [Pd(MeCN)4][BF4]2. These complexes act as metalloreceptors to aromatic amines such as p‐aminopyridine (pap), m‐aminopyridine (map) and the DNA nucleobases adenine and guanine. Binding occurs through simultaneous first‐ and second‐sphere coordination. This involves three separate interactions: first‐sphere σ donation from an aromatic N atom to the Pd centre, second‐sphere hydrogen bonds between the NH2 group and polyether O atoms, and π stacking between the electron‐poor aromatic rings of the substrate and the electron‐rich aromatic spacing units of the receptor. 1H NMR spectra exhibit chemical shift changes indicative of the H‐bonding and π‐stacking interactions in solution. X‐ray structures for thiacyclophane 1, metalloreceptor [Pd(1)(MeCN)][BF4] (3), metalloreceptor/model substrate complexes [Pd(1)(pap)][BF4 (5) and [Pd(2)‐(pap)][BF4] (7), and metalloreceptor/nucleobase complexes [Pd(1)(adenine)][BF4] (13), [Pd(2)(adenine)][BF4] (14) and [Pd(1)(guanine‐BF3)][BF4] (15b) show details of these interactions in the solid state.Keywords
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