Reaction of bis(alkyl/aryl)-2-pyridylalcoholate ligands (a-g) with [ReOCl 4 ](NBu 4 ) results in the formation of metal-oxo complexes of the general formula [ReOCl 3 (L)](NBu 4 ) (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 [CuCl 2 ‚2(H 2 O)] 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).
Reaction of [NBu4] [ReOC1,] (1) with bidentate salicylidene amine ligands (salen = HL) (2a-c) leads to the formation of monomeric octahedral rhenium(V) compounds of formula [ReOCl(L),] (3a-c). Spectroscopic data indicate asymnietric arrangement of the ligands in the complexes. This is confirmed by the X-ray crystal structures of 3b and 3c. Complexes 3a, b have been tested as catalysts for the epoxidation of cyclooctene. No evidence for decomposition of the catalysts is observed during tho reaction (as in the case for tri-and tetradentate salen complexes). No undesired byproducts are formed in the catalytic reactions.
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