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 [CuCl2·2(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).