Rhenium, palladium, and copper pyridylalkoxide complexes: Synthesis, structural characterization, and catalytic application in epoxidation reactions

Reaction of bis(alkyl/aryl)-2-pyridylalcoholate ligands (a-g) with [ReOCl4](NBu4) results in the formation of metal-oxo complexes of the general formula [ReOCl3(L)](NBu4) (2, 3) and [ReOCl(L)(2)] (4, 5), with L = bis(alkyl/aryl)-2-pyridylalcoholate. Molecular structures of the complexes 2a, 4a, and 5a have been determined by single-crystal X-ray diffraction studies. Besides the expected crystal structure of 4a, where an alkoxide site of one of the ligands is coordinated trans to the rhenyloxo fragment, complex 5a shows a rare example of a trans chloro-oxo [ReOCl(L)(2)] connectivity. Additionally, starting from Pd(OAc)(2) and [CUCl2 center dot 2(H2O)] complexes of the form [M(L)(2)] (M = Cu, Pd) (6a-g and 8a) were prepared. For complexes 6a and 8a molecular structures have been determined by single-crystal X-ray diffraction studies, which showed the expected square planar geometry with the pyridine ring nitrogens situated mutually in trans position. Complexes 3, 4, 6, and 8 were tested in the epoxidation reaction of cyclooctene with TBHP (tert-butylhydrogenperoxide).