Oxovanadium(V) complexes with tripodal bisphenolate and monophenolate ligands: Syntheses, structures and catalytic activities

The reactions between [VO(acac)(2)] (acac(-) = acetylacetonate) and the tripodal amino bisphenols 6,6'-(((2-morpholinoethyl)azanediyl)bis(methylene))bis(2,4-di-tert-butylphenol) (H2L1) and 6,6'-(((thiophen-2-ylmethyl) azanediyl)bis(methylene))bis(2,4-di-tert-butylphenol) (H2L2) as well as the tetradentate amino phenol 2,2'-((3,5-di-tert-butyl-2-hydroxybenzyl)azanediyl)bis(ethan-1-ol) (H3L3) afford the complexes [VO(L-1)(OMe)] (1), [VO (L-2)(acac)] (2) and [VO(L-3)] (3), correspondingly. Complexes 1 and 3 can also be prepared using VOSO4 center dot xH(2)O or [VO(OPr)(3)] as vanadium precursors. When [VO(acac)(2)] or VOSO4 center dot xH(2)O is used, mononuclear oxovanadium (V) complexes are formed upon oxidation of the metal precursor. Single crystal X-ray structure analysis show that complexes 1 and 2 have distorted octahedral coordination spheres, in which the amino bisphenolate coordinates in a tetradentate or tridentate manner, respectively, and the coordination spheres are completed by methoxy or acetylacetonato ligands. Complex 3 has a slightly distorted trigonal bipyramidal geometry with an NO4 coordination environment. All three complexes can catalyze epoxidation of cis-cyclooctene at 50 degrees C with tert-butyl hydroperoxide (TBHP) or H2O2 as an oxygen source, and sulfoxidation of thioanisole or methyl-ptolylsulfide proceeds at 25 degrees C using the same oxidants.