Bidentate Lewis Base Adducts of Methyltrioxorhenium(VII) and Their Application in Catalytic Epoxidation

Abstract

Methyltrioxorhenium(VII) (MTO) forms octahedral adducts with bidentate Lewis bases. These complexes were isolated and fully characterized, including X-ray crystallography. The compounds display distorted octahedral geometry in the solid state with a tendency of disorder concerning the Re central atom. At elevated temperatures, they undergo rapid ligand-exchange reactions in solution. The ease of this ligand exchange depends mainly on the Lewis basicity of the ligand. The more Lewis basic the ligand is, the stronger the metal-ligand interaction is, as can be shown by NMR spectroscopy. All examined complexes are temperature stable but quite sensitive to light and moisture. In the presence of H(2)O(2), the complexes form very active and highly selective epoxidation catalysts. Peroxo complexes are generated, and at least one of the Re-N interactions is cleaved during this process. Total ligand dissociation only occurs in the case of very weakly coordinating bidentate ligands. The peroxo complexes of the MTO Lewis base adducts are, in general, more sensitive to water than MTO itself.

Synthesis of di‐nitrogen Schiff base complexes of methyltrioxorhenium(VII) and their application in epoxidation with aqueous hydrogen peroxide as oxidant

“…The same situation was also observed by others in the literature. [24,38] However, the stretching vibrations of iminic bonds in the complexes occur between 1618 and 1648 cm and ν asym (Re O) are observed in the above complexes. Generally the difference between the symmetric and asymmetric stretching of ReO 3 moiety is related to the geometry of the MTO complexes.…”

“…The results are same as those of complexes c4 and c7 reported by us recently. [34] As is known for most structurally characterized bidentate Lewis base complexes of MTO, [24,25] the three oxygen atoms display a pyramidal facial arrangement. The two nitrogen atoms from di-nitrogen Schiff base and two double-bonded oxygen atoms occupy the equatorial position, while the methyl group and the remaining oxygen atom reside in the apical sites in a trans position.…”

Chromophoric Lewis Base Adducts of Methyltrioxorhenium: Synthesis, Catalysis and Photochemistry

“…No significant differences in catalytic performance were found. The behaviour of the complexes under irradiation with UV light was investigated by means of 17 O-NMR and UV/Vis spectroscopy. The herein exposed experiments aimed for probing potential beneficial effects of chromophoric N-donor ligands in MTO adducts, as they might activate the catalytic system by providing additional energy for weakening bonds that have to be broken during the catalytic cycle.…”

Methyltrioxorhenium‐Catalyzed Epoxidation‐Methanolysis of Glycals under Homogeneous and Heterogeneous Conditions

“…MTO reacts with monodentate and bidentate nitrogen ligands to give trigonal bipyramidal and distorted octahedral adducts, respectively. [36] Since a strong influence of added nitrogen ligands has been observed in a related MTO-catalyzed epoxidation-phosphorylation of glycals either in the reaction rate or the stereoselectivity, [37] a series of pre-formed amine-MTO compounds 5 -7 has been also prepared and tested in this reaction [ …”