Rhenium, Palladium, and Copper Pyridylalkoxide Complexes:  Synthesis, Structural Characterization, and Catalytic Application in Epoxidation Reactions

Abstract

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).

Metal-ligand bond lengths and strengths: are they correlated? A detailed CSD analysis

“…Two alkoxides examples are: bis(dimethylamino-2-methyl-2-propanolato)copper(II) (BESHUD) [18] with the two Cu--O bond lengths at 1.864 Å and bis(9-(2-pyridyl)fluoren-9-olato-N,O)copper(II) methanol solvate (LIVFAY) [19] with the two Cu--O bond lengths at 1.911 and 1.912 Å . These shorter bonds are to be ascribed partly to the fact that the alcoholate is part of a N-containing chelating ligand and that in this case the coordination number is 4, as there are no axial ligands present.…”

Oxidorhenium(V) Complexes with Oxazolinylmethoxido Ligands – Structure and Catalytic Epoxidation

“…[12,13,29,42] The structure of the active species is as yet unidentified. One possible deactivation of the catalyst could be an irreversible oxidation to a colourless perrhenate(VII) ion, which has been observed in other epoxidation reactions.…”

“…One possible deactivation of the catalyst could be an irreversible oxidation to a colourless perrhenate(VII) ion, which has been observed in other epoxidation reactions. [29] Another possible inhibition of catalysis is the formation of tert-butyl alcohol, the reduction product of TBHP, which could compete with TBHP for empty coordination sites on the Re centre.…”

Oxidorhenium(V) Complexes with Tridentate and Tetradentate Phenol‐Based Ligands

“…[16,17,19,41,45] Recently, we investigated complexes of the type [ReOCl 2 (L)(PPh 3 )] and [ReOCl(L) 2 ] (L = oxo iminato ligands) in the reaction of cyclooctene with TBHP in which a conversion to the epoxide of 55 % was observed. [18,20] To explore the influence of additional donors in the catalyst on the catalytic activity, we tested rhenium complexes 1 to 14 in the model reaction shown in Scheme 4.…”

“…For this reason, more stable oxidorhenium(V) complexes were also investigated as catalysts in epoxidations albeit as yet with limited success. [16][17][18][19][20] The rhenium(V) systems investigated so far show significantly lower activity or productivity than rhenium(VII) systems. In contrast to applications in oxidation reactions, oxidorhenium(V) compounds were recently found to be catalysts in several other reactions.…”