Dicopper(II) complexes of a tridentate pyrimidine derived Schiff base ligand: Syntheses, crystal structures and catalytic reactions

Three new dinuclear Cu(II) complexes, [Cu₂(L)₂(L ₁)]PF₆ (1), [Cu₂(L)₂(L ₂)]PF₆ (2) and [Cu₂(L)₂(L ₃)]PF₆ (3), of a potentially tridentate NNO-donor Schiff base ligand [HL = 2-(2-(4,6-dimethylpyrimidin-2-yl)hydrazono)methyl)phenol] and the ancillary ligands [HL₁ = benzoic acid, HL₂ = salicylic acid, HL₃ = 4-amino benzoic acid] have been synthesized and characterized by elemental analyses, IR, single crystal X-ray crystallography, spectroscopic, electrochemical and catalytic studies. The ligand HL is the [1+1] condensation product of salicylaldehyde with 2-hydrazino-4,6-dimethyl pyrimidine. In the complexes 1, 2 and 3, two Cu(II) centers are bridged by the carboxylic oxygen atoms of the respective acid moiety. All the metal centres have square-based pyramidal (SP) geometries (Γ = 0.120, 0.124, 0.109 for 1, 2 and 3, respectively). The dinuclear Cu(II) complexes show high catalytic activity and selectivity for the epoxidation of styrene, cyclohexene and cyclooctene using tert-butyl hydroperoxide (TBHP) as the oxidant.