Visible light-induced partial oxidation of olefins on Cr-containing silica with molecular oxygen

Photocatalytic oxidation of olefins on Cr-containing silica with molecular oxygen by visible light irradiation (lambda > 400 nm) has been investigated. Cr-SiO(2) catalyst prepared by a conventional sol-gel method, containing highly dispersed chromate species, catalyzes efficient olefin oxidation with very high selectivity for partially oxidized products (>90%), whereas semiconductor TiO(2) promotes complete decomposition (CO(2) production). The Cr-SiO(2) catalyst shows much higher activity than Cr/SiO(2) prepared by an impregnation method or Cr proportional variant MCM-41 prepared by a templating method. ESR analysis reveals that photoirradiation of the chromate species with a tetrahedral coordination (T(d)(6+)) on Cr/SiO(2) and Cr proportional variant MCM-41 catalysts leads to the formation of excited state T(d)(5+) species (T(d)(5+*)), while irradiation to T(d)(6+) on Cr-SiO(2) produces T(d)(4+*) species. This can be explained by a homogeneous T(d)(6+) arrangement with Si species on the Cr-SiO(2) catalyst. On the strongly reduced T(d)(4+*), olefins are strongly attracted by an electron and/or proton donation, resulting in high oxidation activity. The Cr-SiO(2) catalyst is applicable to partial oxidation of various aliphatic and aromatic olefins with very high selectivity, and does not promote undesirable dimerization. The obtained findings suggest a potential use of Cr-SiO(2) as an efficient and recyclable heterogeneous photocatalyst for partial oxidation of olefins.     

Highly ordered chevron-shaped arrays of continuous copper nano-dot lines formed by electroless deposition on hydrogen-terminated Si(111) surfaces

We have succeeded in forming highly ordered chevron-shaped arrays of continuous copper nano-dot lines by electroless deposition on hydrogen-terminated Si(111) (H-Si(111)) surfaces. Detailed investigations have shown that tiny Cu clusters are preferentially formed at step edges when the electroless deposition is carried out in a deoxygenated neutral aqueous solution of a low Cu2+ concentration (less than 10 microM) with pH approximately = 7. This finding was combined with highly ordered step-edge lines on H-Si(111) prepared by the previously reported method of Teflon scratching and NH4F etching, which has led to the above success. The present result indicates that designed ordered metal nanowires can be produced by the electroless deposition method, using H-Si(111) surfaces with well-regulated step lines as a substrate.     

A dendrimer approach to high-spin polycarbenes. Conversion of connectivity from disjoint to non-disjoint by perturbation of nonbonding molecular orbital coefficients

[structure: see text] Pentakis(diazo) compound was prepared by coupling 3,5-bis[4-[diazo(4-tert-butyl-2,6-dimethylphenyl)methyl]-3,5-dibromophenylethynyl]phenylacetylene with bis(4-iodo-2,6-dimethylphenyl)diazomethane under Sonogashira reaction conditions. Pentakis(carbene) generated by irradiation of the pentakis(diazo) compound was shown to have a high-spin state with S = 4.4 at 2.0 K.     

Reactions of 2-phospholene 1-oxides with bromine in some media: Facile preparation of bromohydrin derivatives of 2-phospholenes

Reactions of 1-phenyl- and 1-methoxy-2-phospholene 1-oxides with bromine in aqueous organic solvents or in a protic medium, such as methanol, easily afforded the corresponding 2-bromo-3-hydroxy- or 2-bromo-3-methoxyphospholane 1-oxide derivatives. The reaction mechanism was postulated based on the stereochemistry of the products.     

Colloidal metal dispersions and metal complexes in hydrocarbons

Stable dispersions of colloidal metals in hydrocarbons have been prepared by a novel phase-transfer method. The metals were gold, silver, palladium and ruthenium; the hydrocarbons were n-hexane, cyclohexane and benzene. The phase transfer of colloidal metal particles from an aqueous phase to a hydrocarbon phase was achieved by adding salt to the emulsion of hydrocarbon in the aqueous suspension of metal with sodium oleate. The salts were sodium chloride, magnesium chloride, sodium sulfate, etc. The size distributions of the metal particles in the resulting hydrocarbon suspensions were almost the same as that of the original aqueous suspension. The dispersions of colloidal metals in hydrocarbons were stable for a long period of time without the addition of hydrocarbon-soluble stabilizer. The critical phase-transfer concentrations of various salts were determined. The phase-transfer powers of cations were larger than those of anions. Those of divalent and trivalent cations were exceedingly larger than that of the monovalent cation. The concentration of colloidal metal dispersed in hydrocarbon was achieved by using the phase-transfer method.