MOLECULAR RECEPTORS FOR ADENINE AND GUANINE EMPLOYING METAL COORDINATION, HYDROGEN-BONDING AND PI-STACKING INTERACTIONS

Thiacyclophane ligands 1 and 2, containing a meta-xylyldithiaether uni t, an aromatic spacing unit and a polyether chain, were prepared in go od yield in a three-step synthesis, The macrocyclic organopalladium co mplexes [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)]I[BF4](2). These complexes act as metalloreceptors to arom atic amines such as p-aminopyridine (pap), m-aminopyridine (map) and t he DNA nucleobases adenine and guanine. second-sphere coordination. Th is involves three separate interactions: first-sphere a donation from an aromatic N atom to the Pd centre, second-sphere hydrogen bonds betw een the NH2 group and polyether O atoms, and pi stacking between the e lectron-poor aromatic rings of the substrate and the electron-rich aro matic spacing units of the receptor, H-1 NMR spectra exhibit chemical shift changes indicative of the H-bonding and pi-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/nucleo base 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.