| Both epoxidation of olefins and sulfoxidation of thioethers are the important reactions in organic synthesis, because their products can be easily converted to large variety of compounds. In terms of atom efficiency, aqueous hydrogen peroxide would be the ideal oxidant since it produces water as the sole by-product and can therefore be classified as the ultimate green oxidant. Moreover, for industrial applications, the development of epoxidation and sulfoxidation systems using cheap and nontoxic metal complexes as catalysts is significant. To achieve this goal, we designed and synthesized a series of dinuclear 8-quinolinolato titanium(Ⅳ) complexes [HQ-Ti], and investigated their catalytic efficiency in catalyzing the epoxidation of olefins with H2O2. We applied a series of hexadentate binding 8-quinolinolato manganese(Ⅲ) complexes [Q3MnⅢ] to catalyzing the sulfoxidation of thioether with H2O2. Our works are summarized in details as follows:1) We designed and synthesized a series of dinuclear oxo-bridge or organic oxo- or nitro-bridge 8-quinolinolato titanium(Ⅳ) complexes, FT-IR,DRUV-VIS and Ti contents of the HQ-Ti samples were taken to identify thiers structure. After a series of tests, we found that these complexes could efficiently catalyze the epoxidation of aromatic and cyclic olefins, chain alkene and olefinic alcohols with H2O2, in water-acetone media with ammonium acetate and acetic acid as additives. The obtained results indicate that the substituents of HQ ligand significantly influence the catalytic efficiency of the HQ-Ti complexes (10-54%). The halogen substituents could improve catalysts epoxidation activities. Besides that, this epoxidation system has many advantages, such as utilization of more cost-effective and green water-acetone solvent, very catalytic efficiency and could catalyze many kinds of olefins, facile operation, and so on.2) Based on the stepwise overlay of UV-vis spectra for the reaction mixture, combined with the characterization results of FT-IR and TG-DSC, we proposed a reasonable mechanism for the HQ-Ti complexes catalytic cycle: With the help of NH4OAc-HOAc, a Ti-O-Ti bridge bond of di-μ-oxo HQ-Ti in the reaction media may be cleaved to form a mono-μ-oxo HQ-Ti species which reacts with H2O2 to form an active Ti(Ⅳ) peroxy species through opening the Ti-O-ligand bonds. This peroxy species may be returned to the mono-u-oxo HQ-Ti species through transferring its peroxygen atom to alkenes, and then the catalyst regeneration.3) The influence of the reaction temperature, solution, additives and oxidants were studied. After a series of tests, we found the Q3MnⅢcomplexes can highly efficiently catalyze the sulfoxidation thioethers (76-93%) and DMSO (86-99%) with H2O2, in water-acetone media with ammonium acetate and acetic acid as additives. The ligand's halogen substituents could improve the catalytic efficiency of Q3MnⅢcomplexes, and this is likely that they can strengthen the distorted effect of Q3MnⅢ, as supported by B3LYP/6-311G (d) calculation. Besides that, this sulfoxidation system has many advantages, such as utilization of more cost-effective and green water-acetone solvent, very high catalytic efficiency and stability, facile operation, and so on.4) Based on the stepwise overlay of UV-vis spectra for the reaction mixture, we proposed that in the presence of NH4OAc-HOAc or NH4OAc, the Q3MnⅢeasily cleaves the longest Mn-O bond to form a pentadente Q3MnⅢ-OAc with a pendant hydroxyl group. Then, the Q3MnⅢ-OAc rapidly interacts with H2O2 to form the corresponding Q3MnⅢ-OOAc. However, with the help of NaH2PO4, Q3MnⅢcould convert to a high valent Q3MnⅤ=O species. Both of Q3MnⅢ-OOAc and Q3MnⅤ=O may eventually return to the Q3MnⅢthrough directly tranfering its O atom to thioanisole due to its good oxidation capacity.
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