Four μ_4-oxo-bridged copper(II) complexes: magnetic properties and catalyticapplications in liquid phase partial oxidation reactionst

摘要

Four copper(II) complexes, [Cu_4(O)(L")_2(CH_3COO)_4] with N_2O-donor Schiff-base ligands, whereHL~1 =4-methyl-2,6-bis(cyclohexylmethyliminomethyl)phenol for complex1, HL~2= 4-methyl-2,6-bis(phenylmethyliminomethyl)phenol for complex 2.CH_3CN,HL~3= 4-methyl-2,6-bis(((3-tri-fluoro-methyl)phenyl)methyliminomethyl)phenol for complex 3, HL~4=4-methyl-2,6-bis(((4-tri-fluoro-methyl)phenyl)methyliminomethyl)phenol for complex 4, were synthesized and characterized byelemental analysis, FT-IR, UV-vis spectroscopy and finally by single crystal X-ray diffraction study.X-Ray analysis reveals that all of these are μ_4-oxo-bridged tetrameric copper(II) complexes. Four copperatoms arrange themselves around an oxygen atom tetrahedrally. Magnetic susceptibility measurementsshow 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 asheterogeneously by immobilizing the metal complexes over 2D-hexagonal mesoporous silica. Theresults obtained in both the catalytic conditions show that the olefins are converted to the respectiveepoxides in good yield together with high selectivity.