Novel H-Bonded Synthons in Copper Supramolecular Frameworks with Aminoethylpiperazine-Based Ligands. Synthesis, Structure and Catalytic Activity.

New Schiff base complexes [Cu(HL)(L)(N)]∙2HO () and [CuL(N)]∙HO () were synthesized. The crystal structures of and were determined by single-crystal X-ray diffraction analysis. The HL ligand results from the condensation of salicylaldehyde and 1-(2-aminoethyl)piperazine, while a new organic ligand, HL, was formed by the dimerization of HL via a coupling of two piperazine rings of HL on a carbon atom coming from DMF solvent. The dinuclear building units in and are linked into complex supramolecular networks through hydrogen and coordination bondings, resulting in 2D and 1D architectures, respectively. Single-point and broken-symmetry DFT calculations disclosed negligible singlet-triplet splittings within the dinuclear copper fragments in and . Catalytic studies showed a remarkable activity of and towards cyclohexane oxidation with HO in the presence of nitric acid and pyridine as promoters and under mild conditions (yield of products up to 21%). Coordination compound also acts as an active catalyst in the intermolecular coupling of cyclohexane with benzamide using di-tert-butyl peroxide (BuOOBu) as a terminal oxidant. Conversion of benzamide at 55% was observed after 24 h reaction time. By-product patterns and plausible reaction mechanisms are discussed.