Diimine copper(II) complexes as building blocks for microporous catalytic materials

New copper(II) complexes with tridentate diimine ligands, containing imidazolate-bridging groups, have been prepared as precursors of supramolecular-coordination-chemistry-based assemblies, designed to act as oxidation catalysts. These complexes were isolated as mono-, di- and polymeric or cyclic supramolecular species. In solution, solvent- and pH-dependent equilibria between the mono- and dinuclear complexes, or the mono- and the corresponding polymeric species were detected. Those species were characterized by different spectroscopic techniques (UV/Vis, IR, Raman and EPR), and the X-ray crystallographic structure was determined for one of them. The catalytic activity of the dinuclear and polymeric species in the oxidation of phenol substrates by molecular oxygen were verified, by monitoring the corresponding quinone formation. Cyclic hexa- or tetranuclear copper(II) species, exhibiting imidazolate-bridge groups between the copper centres, were observed to be better catalysts then the analogous dinuclear ones, mainly due the interaction of the substrate with the catalyst hydrophobic cavity. A modulation of the cavity size seems strongly affect the reactivity of these systems.