We present here that easily available organic salts can stabilize/modify niobium (Nb) oxo-clusters. The as-synthesized Nb oxo-clusters have been characterized by various methods. These Nb oxo-clusters were catalytically active for the epoxidation of allylic alcohols and olefins with H2O2 as an oxidant. Notably, Nb-OC@TBAF-0.5 appeared as highly dispersed nanosized particles and showed the highest catalytic activity, which can be attributed to the following reasons on the basis of characterization. First, the strong coordination of fluorine ions with Nb sites and the steric protection with bulky organic cations led to high stabilization and dispersion of the oxo-clusters in the course of the reaction. Second, a hydrogen-bond interaction between the coordinated fluorine atom and the −OH group of allylic alcohol favored the epoxidation reaction. Third, the electron density of Nb sites decreased due to the strong electron-withdrawing ability of F– adjacent to Nb sites, thus promoting the electrophilic oxygen transfer to the CC bond.

The alkane oxidation under mild conditions occupies an important position in the chemical industry. Herewith, we have designed a novel class of ionic liquid ([TBA][Pic])-stabilized vanadium oxo-clusters (TBA=tetrabutylammonium; Pic= picolinate...

Oxidative desulfurization is a highly effective approach to decrease the sulfur content in transportation fuel and has become an attractive research topic in recent years. Herewith, we have developed a new kind of carboxylic acid-functionalized imidazolium-based ionic liquid-stabilized Ti oxoclusters via a solvothermal method. The as-synthesized Ti oxoclusters were investigated by elemental analysis, Fourier transform infrared spectroscopy, diffuse reflectance UV–vis, X-ray diffraction, thermogravimetric analysis, high-resolution transmission electron microscopy (HRTEM), and high-angle annular dark field–scanning TEM. Characterization indicated that Ti oxoclusters existed in the form of subnanosized structure and uniformly dispersed with an average particle size of ca. 1 nm due to the protection role of the ionic liquids (ILs). Especially, Ti oxo–HSO4 afforded a superior catalytic activity in the extraction and catalytic oxidative desulfurization process with MeOH as an extractant and H2O2 as an oxidant. The full removal of dibenzothiophene in model fuels was achieved within 30 min at 60 °C. Besides, the Ti oxoclusters were robust and exhibited high stability in consecutive catalytic recycles. The parent Ti oxoclusters treated with H2O2 can afford Ti–OOH species, which was catalytically active species. The anion HSO4 – in IL played a crucial role in the activation of Ti–hydroperoxo species by forming hydrogen bonds. This may provide a new insight into the construction of metal oxoclusters for oxidative desulfurization.

We present here a new class of niobium oxoclusters that are stabilized effectively by carboxylate ionic liquids. These functionalized ILs are designated as [TBA][LA], [TBA][PA], and [TBA][HPA] in this work, in which TBA represents tetrabutylammonium and LA, PA, and HPA refer to lactate, propionate, 3‐hydroxypropionate anions, respectively. The as‐synthesized Nb oxoclusters have been characterized by use of elemental analysis, NMR, IR, XRD, TGA, HRTEM. It was found that [TBA][LA]‐stabilized Nb oxoclusters (Nb−OC@[TBA][LA]) are uniformly dispersed with an average particle size of 2–3 nm and afforded exceptionally high catalytic activity for the selective oxidation of various thioethers. The turnover number with Nb−OC@[TBA][LA] catalyst was over 56 000 at catalyst loading as low as 0.0033 mol % (1 ppm). Meantime, the catalyst also showed the high activity for the epoxidation of olefins and allylic alcohols by using only 0.065 mol % of catalyst (50 ppm). The characterization of 93Nb NMR spectra revealed that the Nb oxoclusters underwent structural transformation in the presence of H2O2 but regenerated to their initial state at the end of the reaction. In particular, the highly dispersed Nb oxoclusters can absorb a large amount of polar organic solvents and thus were swollen greatly, which exhibited “pseudo” liquid phase behavior, and enabled the substrate molecules to be highly accessible to the catalytic center of Nb oxocluster units.

A mononuclear tantalum complex bonded to a peroxocarbonate ligand has been proved to be particularly important in the epoxidation reactions.