Imidazolium-based ionic liquids that contain perrhenate anions are very efficient reaction media for the epoxidation of olefins with H2O2 as an oxidant, thus affording cyclooctene in almost quantitative yields. The mechanism of this reaction does not follow the usual pathway through peroxo complexes, as is the case with long-known molecular transition-metal catalysts. By using in situ Raman, FTIR, and NMR spectroscopy and DFT calculations, we have shown that the formation of hydrogen bonds between the oxidant and perrhenate activates the oxidant, thereby leading to the transfer of an oxygen atom onto the olefin demonstrating the special features of an ionic liquid as a reaction environment. The influence of the imidazolium cation and the oxidant (aqueous H2O2, urea hydrogen peroxide, and tert-butyl hydrogen peroxide) on the efficiency of the epoxidation of cis-cyclooctene were examined. Other olefinic substrates were also used in this study and they exhibited good yields of the corresponding epoxides. This report shows the potential of using simple complexes or salts for the activation of hydrogen peroxide, owing to the interactions between the solvent medium and the active complex.

Several Schiff‐base ligands readily form complexes with methyltrioxorhenium(VII) (MTO) by undergoing a hydrogen transfer from a ligand‐bound OH group to a ligand N atom. The resulting complexes are stable at room temperature and can be handled and stored in air without problems. Due to the steric demands of the ligands they display distorted trigonal‐bipyramidal structures in the solid state, as shown by X‐ray crystallography, with the O− moiety binding to the Lewis acidic Re atom and the Re‐bound methyl group being located either in cis or trans position to the Schiff base. In solution, however, the steric differences seem not to be maintained, as can be deduced from 17O NMR spectroscopy. Furthermore, the Schiff‐base ligands exchange with donor ligands. Nevertheless, the catalytic behaviour is influenced significantly by the Schiff bases coordinated to the MTO moiety, which lead either to high selectivities and good activities or to catalyst decomposition. A large excess of ligand, in contrast to the observations with aromatic N‐donor ligands, is detrimental to the catalytic performance as it leads to catalyst decomposition.

A highly selective and efficient oxidation of sulfides to sulfoxides is presented. The reactions were carried out at room temperature in the absence of a catalyst in the ionic liquid [Bmim][BF 4 ] (Bmim = 1-butyl-3-methylimidazolium) using aqueous H 2 O 2 (35%) as oxidant. The products were obtained in high yields. Compared to the analogous reactions in organic solvents, this system can be recycled without significant loss of activity and selectivity. Additionally, the reaction mechanism was examined by IR, Raman and NMR spectroscopy. Based on these examinations, it appears that the crucial step during the oxidation procedure is the formation of a hydrogen bond between the ionic liquid and the oxidant.