Keigo Kamata

Epoxides are an important class of industrial chemicals that have been used as chemical intermediates. Catalytic epoxidation of olefins affords an interesting production technology. We found a widely usable green route to the production of epoxides: A silicotungstate compound, [gamma-SiW10O34(H2O)2]4-, is synthesized by protonation of a divacant, lacunary, Keggin-type polyoxometalate of [gamma-SiW10O36]8- and exhibits high catalytic performance for the epoxidation of various olefins, including p

It goes on the dicopper core! A monomeric γ-Keggin silicotungstate with a dicopper core that is bridged by two μ-1,1-azido ligands catalyzes oxidative alkyne homocoupling reactions whereby various kinds of aromatic and aliphatic alkynes are selectively converted into the corresponding diynes (see picture).

The dicopper-substituted gamma-Keggin silicotungstate TBA 4[gamma-H2SiW10O36Cu2(mu-1,1-N3)2] (I, TBA = tetra- n-butylammonium) could act as an efficient precatalyst for the regioselective 1,3-dipolar cycloaddition of organic azides to alkynes. Various combinations of substrates (four azides and eight alkynes) were efficiently converted to the corresponding 1,2,3-triazole derivatives in excellent yields without any additives. The present system was applicable to a larger-scale cycloaddition of be

The tetra-n-butylammonium (TBA) salt of the divacant Keggin-type polyoxometalate [TBA](4)[gamma-SiW(10)O(34)(H(2)O)(2)] (I) catalyzes the oxygen-transfer reactions of olefins, allylic alcohols, and sulfides with 30 % aqueous hydrogen peroxide. The negative Hammett rho(+) (-0.99) for the competitive oxidation of p-substituted styrenes and the low value of (nucleophilic oxidation)/(total oxidation), X(SO)=0.04, for I-catalyzed oxidation of thianthrene 5-oxide (SSO) reveals that a strongly electrop

Peroxide in, phenol out: The catalyst [γ-PW(10)O(38)V(2)(μ-OH)(2)](3-) showed high activity in the hydroxylation of various aromatic compounds with aqueous H(2)O(2). The system was regioselective, producing para-phenols from monosubstituted benzene derivatives. Furthermore, alkylarenes with reactive side-chain C sp 3-H bonds could be chemoselectively hydroxylated without significant formation of side-chain oxygenated products.

The reaction of peroxotungstates (H(2)WO(4) + H(2)O(2)) with H(2)SeO(4) gave the novel selenium-containing dinuclear tungsten species, (TBA)(2)[SeO(4){WO(O(2))(2)}(2)] (I, TBA = [(n-C(4)H(9))(4)N](+)), which was characterized by elemental analysis, IR, Raman, UV-vis, (77)Se NMR, (183)W NMR, and CSI-MS. Various kinds of homoallylic and allylic alcohols were efficiently epoxidized to the corresponding epoxy alcohols in high yields with 1 equiv. H(2)O(2) with respect to the substrates. Compound I s

[reaction: see text] Ru(OH)x/Al2O3 efficiently catalyzes the heterogeneous aerobic oxygenation or oxidative dehydrogenation of alkylarenes to give the corresponding oxygenated or dehydrogenated products. Catalyst/product separation is very easy, and the recovered catalyst is reusable with retention of the high catalytic performance.

Oxidation optimization: A combination of tungsten and zinc oxides on a SnO2 support (W–Zn/SnO2) is a heterogeneous and reusable solid catalyst for selective oxidation with aqueous H2O2. With it, various substrates, such as alkenes, amines, silanes, and sulfides, were oxidized into the corresponding products in high yields (see scheme). The catalyst can be reused several times without an appreciable loss in catalytic performance.

By using the selenium-containing dinuclear peroxotungstate at 0.005-0.1 mol%, various kinds of sulfides could be converted into the corresponding sulfoxides or sulfones in excellent yields with one or two equivalents of H(2)O(2) with respect to the sulfide, respectively.

The highly chemo-, regio-, and diastereoselective and stereospecific epoxidation of various allylic alcohols with only one equivalent of hydrogen peroxide in water can be efficiently catalyzed by the dinuclear peroxotungstate, K2[[W(=O)(O2)2(H2O)]2(mu-O)].2H2O (I). The catalyst is easily recycled while maintaining its catalytic performance. The catalytic reaction mechanism including the exchange of the water ligand to form the tungsten-alcoholate species followed by the insertion of oxygen to th

A divanadium-substituted phosphotungstate, [γ-PW(10)O(38)V(2)(μ-OH)(2)](3-) (I), showed the highest catalytic activity for the H(2)O(2)-based epoxidation of allyl acetate among vanadium and tungsten complexes with a turnover number of 210. In the presence of I, various kinds of electron-deficient alkenes with acetate, ether, carbonyl, and chloro groups at the allylic positions could chemoselectively be oxidized to the corresponding epoxides in high yields with only an equimolar amount of H(2)O(2

In sharp contrast with acid-, photo-, and oxidation-catalysis by polyoxometalates, base catalysis by polyoxometalates has scarcely been investigated. The use of polyoxometalates as base catalysts have very recently received much attention and has been extensively investigated. Numerous mono- and polyoxometalate base catalyst systems effective for the chemical fixation of CO2, cyanosilylation of carbonyl compounds, and C–C bond forming reactions have been developed. Mono- and polyoxometalate base

Mesoporous β-MnO₂ nanoparticles were synthesized by a template-free low-temperature crystallization of Mn⁴⁺ precursors (low-crystallinity layer-type Mn⁴⁺ oxide, <i>c</i>-distorted H⁺-birnessite) produced by the reaction of MnO₄^- and Mn²⁺. The Mn starting materials, pH of the reaction solution, and calcination temperatures significantly affect the crystal structure, surface area, porous structure, and morphology of the m

A rhombohedral BaRuO₃ nanoperovskite, which was synthesized by the sol-gel method using malic acid, could act as an efficient heterogeneous catalyst for the selective oxidation of various aromatic and aliphatic sulfides with molecular oxygen as the sole oxidant. BaRuO₃ showed much higher catalytic activities than other catalysts, including ruthenium-based perovskite oxides, under mild reaction conditions. The catalyst could be recovered by simple filtration and reused sever