Four mu(4)-oxo-bridged copper(II) complexes: magnetic properties and catalytic applications in liquid phase partial oxidation reactions

Four copper(II) complexes, [Cu-4(O)(L-n)(2)(CH3COO)(4)] with N2O-donor Schiff-base ligands, where HL1 = 4-methyl-2,6-bis(cyclohexylmethyliminomethyl) phenol for complex 1, HL2 = 4-methyl-2,6-bis( phenylmethyliminomethyl) phenol for complex 2 center dot CH3CN, HL3 = 4-methyl-2,6-bis(((3-tri-fluoro-methyl) phenyl) methyliminomethyl) phenol for complex 3, HL4 = 4-methyl-2,6-bis(((4-tri-fluoro-methyl) phenyl) methyliminomethyl) phenol for complex 4, were synthesized and characterized by elemental analysis, FT-IR, UV-vis spectroscopy and finally by single crystal X-ray diffraction study. X-Ray analysis reveals that all of these are mu(4)-oxo-bridged tetrameric copper(II) complexes. Four copper atoms arrange themselves around an oxygen atom tetrahedrally. Magnetic susceptibility measurements show the existence of very strong antiferromagnetic coupling among these ions (J = -210.1 to -271.3 cm(-1)), mediated by the oxygen atoms. Catalysis of the epoxidation of cyclohexene, styrene, a-methylstyrene and trans-stilbene by these complexes has been carried out homogeneously as well as heterogeneously by immobilizing the metal complexes over 2D-hexagonal mesoporous silica. The results obtained in both the catalytic conditions show that the olefins are converted to the respective epoxides in good yield together with high selectivity.