Vanadium(V) complexes with hydrazone and benzohydroxamate ligands: synthesis, structures and catalytic epoxidation
Two structurally similar vanadium(V) complexes, [VOL1L] (1) and [VOL2L] (2), where L1 is the dianionic form of N′-(3,5-dibromo-2-hydroxybenzylidene)-4-methoxybenzohydrazide, L2 is the dianionic form of N′-(3,5-dibromo-2-hydroxybenzylidene)nicotinohydrazide, and L is benzohydroxamate, were prepared and characterized by elemental analysis, infrared spectra, and single crystal X-ray diffraction. 1 crystallizes in the monoclinic space group P2 1 /c, with unit cell dimensions a = 12.0262(7), b = 16.5629(9), c = 12.3449(8) Å, β = 105.160(2)°, V = 2373.4(2) Å3, Z = 4, R 1 = 0.0376, wR 2 = 0.0844, GOOF = 1.058; 2 crystallizes in the monoclinic space group P2 1 /c, with unit cell dimensions a = 10.6439(7), b = 16.1968(9), c = 13.1108(8) Å, β = 104.180(2)°, V = 2191.4(2) Å3, Z = 4, R 1 = 0.0521, wR 2 = 0.1142, GOOF = 1.018. X-ray analysis indicates that vanadium in the complexes are coordinated by phenolate oxygen, imino nitrogen, and enolate oxygen of the hydrazone, two oxygens of the benzohydroxamate, and one oxo, generating octahedral coordination. Oxidations of olefins with the complexes as catalysts were evaluated. The complexes showed effective catalytic efficiency in oxidation of several aliphatic and aromatic substrates under mild conditions, using tert-butyl hydrogen peroxide as oxidant.
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