Molecular Receptors for Adenine and Guanine Employing Metal Coordination, Hydrogen‐Bonding and π‐Stacking Interactions

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)][BF 4 ] ( 3 : L = 1; 4 : L = 2 ) were prepared through palladation of the respective thiacyclophane ligand by reaction with [Pd(MeCN) 4 ][BF 4 ] 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 NH 2 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. 1 H 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)][BF 4 ] ( 3 ), metalloreceptor/model substrate complexes [Pd( 1 )(pap)][BF 4 ( 5 ) and [Pd( 2 )‐(pap)][BF 4 ] ( 7 ), and metalloreceptor/nucleobase complexes [Pd( 1 )(adenine)][BF 4 ] ( 13 ), [Pd( 2 )(adenine)][BF 4 ] ( 14 ) and [Pd( 1 )(guanine‐BF 3 )][BF 4 ] ( 15b ) show details of these interactions in the solid state.