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

Three new dinuclear Cu(II) complexes, [Cu-2(L)(2)(L-1)]PF6 (1), [Cu-2(L)(2)(L-2)]PF6 (2) and [Cu-2(L)(2)(L-3)]PF6 (3), of a potentially tridentate NNO-donor Schiff base ligand [HL = 2-(2-(4,6-dimethylpyrimidin-2-yl)hydrazon-o)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 (Gamma = 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. (C) 2012 Elsevier Ltd. All rights reserved.