A Versatile Approach to the Intramolecular Organization of Two Bipyridine-Like Chelating Units in a Polytopic Ligand

The synthesis of four novel polypyridyl ligands, in which two 4,6-[bis(2-pyridyl)]pyrimidine units are covalently linked by spacer groups −S− (1), −S−S− (2), −Se− (7), and −Se−Se− (6), is reported. A new unsymmetrical dinucleating ligand 4 was isolated as a by-product in the synthesis of 2 and has been characterized by X-ray crystallography. Copper(II) complexes [(1)Cu](NO3)2·5H2O and [(7)Cu](ClO4)2·6H2O have been isolated, spectroscopic data for which are consistent with tetradentate N4 coordination by the ligands. In situ prepared polynuclear copper(II) complexes of 1 and 7 show different catalytic activities in the cleavage of the phosphodiester 2-hydroxypropyl p-nitrophenyl phosphate. This might be a consequence of the influence of the covalent spacer (S or Se) on the preorganization of two bipyridine-like chelating units in [LCu]2+, which bind two catalytic Cu2+ ions.