•Small Au nanoparticles (<3 nm) were prepared on various supports by impregnation.•Chloride-free Au complex prevents Au atoms from aggregating.•Decomposition temperature of the Au complex is lower than that of HAuCl4.•The Au/SiO2 hydrogenates vinyl group of 1-nitro-4-vinylbenzene selectively.•The Au/SiO2 can be applied for adsorption of unpalatable aroma in drink.A novel simple and easy impregnation method for preparation of small gold (Au) nanoparticle (NP) catalysts (<3 nm) deposited on various supports including silica, which is difficult to be applied for conventional methods, has been developed. Chloride-free and water-soluble precursor, Au complexes coordinated with β-alanine, were successful for the preparing Au NPs, which exhibited an average diameter less than 3 nm. Thermal behavior of the Au complex was investigated by TG-DTA and in situ XAFS. XAFS analyses and DFT calculations revealed a molecular structure of the Au complex to be square-planar coordination structure and mononuclear complex of Au3+. Lower decomposition and reduction temperature of the chloride-free Au complex prevented Au atoms from aggregating and from following growth of Au particles. The prepared Au/SiO2 showed high selectivity for hydrogenation of 1-nitro-4-vinylbenzene into 1-ethyl-4-nitorobenzene and good performance for removal of unpalatable aroma by means of adsorption of polysulfide molecules.Download high-res image (84KB)Download full-size image

The intermolecular hydroaminomethylation and the intramolecular cyclocarbonylation efficiently proceeded on cobalt oxide supported gold nanoparticles. The intermolecular reaction employing terminal olefins and N-isopropylaniline afforded hydroaminomethylated products as a mixture of regioisomers via a common reaction path consisting of hydroformylation, imine formation, and hydrogenation. In contrast, indolinone derivatives were exclusively obtained in the case of 2-alkenylanilines based on the intramolecular cyclocarbonylation mechanism. Both of these reactions were catalyzed by cobalt species derived from cobalt oxide. The active cobalt species were formed via reduction of the oxide support promoted by deposited gold nanoparticles. Characterization of the catalysts before and after the reaction was also performed.

Hydrolytic enantioselective protonation of dienyl esters and a β-diketone catalyzed by phase-transfer catalysts are described. The latter reaction is the first example of an enantio-convergent retro-Claisen condensation. Corresponding various optically active α,β-unsaturated ketones having tertiary chiral centers adjacent to carbonyl groups were obtained in good to excellent yields and enantiomeric ratios (83–99%, up to 97.5:2.5 er).

The oxidation of primary and secondary benzylic alcohols was achieved by using tert-butyl nitrite (t-BuONO) as a stoichiometric oxidant. Various substrates were effectively converted into the corresponding ketones or aldehydes in good to excellent yields. The reaction presumably proceeded by a nitrosyl exchange and a subsequent thermal decomposition of benzylic nitrites. This process would realize an oxidation of alcohols with oxygen in theory by combining with a reproduction of alkyl nitrites from NO and alcohols under an O2 atmosphere. In addition, almost pure oxidized products were readily obtained by simple evaporation of the reaction mixtures since t-BuONO produced only volatile side products.

A treatment of cobalt oxide supported gold nanoparticles (Au/Co3O4) under syngas atmosphere effectively generated a cobalt carbonyl-like active species in the reaction vessel. The preparation of Au/Co3O4 was quite simple and the in situ generated cobalt species could be used as a stable and easy handling alternative for dicobalt octacarbonyl without bothersome purification prior to use. The reactions, which are sensitive to the purity of the dicobalt octacarbonyl, such as the alkoxycarbonylation of epoxides and the Pauson–Khand reaction, smoothly progressed with Au/Co3O4.

One-pot sequences of hydrogenation/hydroamination to form indoles from (2-nitroaryl)alkynes and hydrogenation/reductive amination to form aniline derivatives from nitroarenes and aldehydes were catalyzed by Au nanoparticles supported on Fe2O3. Nitro group selective hydrogenations and successive reactions were efficiently catalyzed under the conditions.

Intermolecular hydroalkoxylation of unactivated olefins catalyzed by the combination of gold(I) and electron deficient phosphine ligands has been developed. Although pairings of unactivated olefins and common aliphatic alcohols gave unsatisfactory results in gold catalyzed hydroalkoxylations, the use of alcohol substrates bearing coordination functionalities such as halogen or alkoxy groups showed great improvement of reactivity.

Kinetic resolution of phosphoryl and sulfonyl esters of 1,1′-bi-2-naphthol has been achieved via the Pd-catalyzed alcoholysis of their vinyl ethers. The highest krel value reached 36.8 with substrate 3c, and (R)-3c 99.0% ee was obtained in 43% isolated yield.Dimethyl 2′-vinyloxy-1,1′-binaphthyl-2-yl phosphateC24H21O5PEe = 94.8%[α]D23=+29.5 (c 1.00, C6H6)Source of chirality: kinetic resolutionAbsolute configuration: (R)Diethyl 2′-vinyloxy-1,1′-binaphthyl-2-yl phosphateC26H25O5PEe = 98.5%[α]D28=+39.6 (c 1.00, C6H6)Source of chirality: kinetic resolutionAbsolute configuration: (R)2-(5,5-Dimethyl-2-oxo-1,3,2-dioxaphosphorinan-2-yloxy)-2′-vinyloxy-1,1′-binaphthaleneC27H25O5PEe = 41.0%[α]D28=+2.7 (c 1.00, C6H6)Source of chirality: kinetic resolutionAbsolute configuration: (R)2′-Vinyloxy-1,1′-binaphthyl-2-yl dicyclohexylphosphinateC34H37O3PEe = 27.4%[α]D28=-0.6 (c 1.00, C6H6)Source of chirality: kinetic resolutionAbsolute configuration: (R)Dimethyl 2′-hydroxy-1,1′-binaphthyl-2-yl phosphateC22H19O5PEe = 73.0%[α]D24=-25.2 (c 1.00, CHCl3)Source of chirality: kinetic resolutionAbsolute configuration: (S)Diethyl 2′-hydroxy-1,1′-binaphthyl-2-yl phosphateC24H23O5PEe = 62.7%[α]D25=-32.2 (c 1.00, CHCl3)Source of chirality: kinetic resolutionAbsolute configuration: (S)2-(5,5-Dimethyl-2-oxo-1,3,2-dioxaphosphorinan-2-yloxy)-2′-hydroxy-1,1′-binaphthaleneC25H23O5PEe = 63.8%[α]D25=-8.5 (c 1.00, CHCl3)Source of chirality: kinetic resolutionAbsolute configuration: (S)2′-Hydroxy-1,1′-binaphthyl-2-yl dicyclohexylphosphinateC32H35O3PEe = 55.2%[α]D25=-26.9 (c 1.00, CHCl3)Source of chirality: kinetic resolutionAbsolute configuration: (S)2′-Vinyloxy-1,1′-binaphthyl-2-yl methanesulfonateC23H18O4SEe = 40.7%[α]D28=-4.4 (c 1.00, C6H6)Source of chirality: kinetic resolutionAbsolute configuration: (R)2′-Vinyloxy-1,1′-binaphthyl-2-yl 4-toluenesulfonateC29H22O4SEe = 45.6%[α]D28=+4.26 (c 1.00, C6H6)Source of chirality: kinetic resolutionAbsolute configuration: (R)2′-Vinyloxy-1,1′-binaphthyl-2-yl 2,4,6-triisopropylbenzenesulfonateC37H38O4SEe = 99.0%[α]D23=+28.0 (c 1.00, C6H6)Source of chirality: kinetic resolutionAbsolute configuration: (R)(aR,R)-2′-Vinyloxy-1,1′-binaphthyl-2-yl camphorsulfonateC32H30O5SDe = 54.8%[α]D23=-11.8 (c 1.00, C6H6)Source of chirality: kinetic resolutionAbsolute configuration: (aR,R)(aR,S)-2′-Vinyloxy-1,1′-binaphthyl-2-yl camphorsulfonateC32H30O5SDe = 95.0%[α]D23=-2.9 (c 1.00, C6H6)Source of chirality: kinetic resolutionAbsolute configuration: (aR,S)2′-Hydroxy-1,1′-binaphthyl-2-yl methanesulfonateC21H16O4SEe = 46.7%[α]D24=-13.7 (c 1.00, CHCl3)Source of chirality: kinetic resolutionAbsolute configuration: (S)2′-Hydroxy-1,1′-binaphthyl-2-yl 4-toluenesulfonateC27H20O4SEe = 51.4%[α]D25=-25.9 (c 1.00, CHCl3)Source of chirality: kinetic resolutionAbsolute configuration: (S)2′-Hydroxy-1,1′-binaphthyl-2-yl 2,4,6-triisopropylbenzenesulfonateC35H36O4SEe = 75.7%[α]D23=-54.6 (c 1.00, CHCl3)Source of chirality: kinetic resolutionAbsolute configuration: (S)(aS,R)-2′-Hydroxy-1,1′-binaphthyl-2-yl camphorsulfonateC30H28O5SDe = 59.5%[α]D23=-22.1 (c 1.00, CHCl3)Source of chirality: kinetic resolutionAbsolute configuration: (aS,R)(aS,S)-2′-Hydroxy-1,1′-binaphthyl-2-yl camphorsulfonateC30H28O5SDe = 58.9%[α]D23=-36.0 (c 1.00, CHCl3)Source of chirality: kinetic resolutionAbsolute configuration: (aS,S)Dimethyl 2′-vinyloxy-(5,5′,6,6′-tetramethyl-1,1′-biphenyl)-2-yl phosphateC20H25O5PEe = 98.1%[α]D24=+21.6 (c 2.30, C6H6)Source of chirality: kinetic resolutionAbsolute configuration: (R)2′-Vinyloxy-(5,5′,6,6′-tetramethyl-1,1′-biphenyl)-2-yl 2,4,6-triisopropylbenzenesulfonateC33H42O4SEe = 66.9%[α]D24=-28.7(c 1.00, C6H6)Source of chirality: kinetic resolutionAbsolute configuration: (R)Dimethyl 2′-hydroxy-(5,5′,6,6′-tetramethyl-1,1′-biphenyl)-2-yl phosphateC18H23O5PEe = 56.6%[α]D25=-18.4 (c 1.00, CHCl3)Source of chirality: kinetic resolutionAbsolute configuration: (S)2′-Hydroxy-5,5′,6,6′-tetramethyl-1,1′-biphenyl-2-yl 2,4,6-triisopropylbenzenesulfonateC31H40O4SEe = 83.0%[α]D24=-48.3 (c 1.00, CHCl3)Source of chirality: kinetic resolutionAbsolute configuration: (S)

Highlights•Au on NiO promoted Ni(II) reduction to produce active Au–Ni bimetallic catalysts.•Reduction of Au(OH)3–Ni(OH)2–NiCO3 coprecipitates with H2 produced Au–Ni alloys.•The Au–Ni alloy catalyzes hydrogenolysis of benzylic alcohols with high selectivity.Gold–nickel bimetallic catalysts were prepared from Au/NiO and Au(OH)3–Ni(OH)2–NiCO3 coprecipitates by treatment with hydrogen. Gold promoted the reduction of Ni(II) to Ni(0) at relatively low temperatures in the range of 100–150 °C, which was confirmed by H2-TPR and in situ XAFS measurements, whereas NiO without Au was not fully reduced even at 300 °C. The obtained catalysts were characterized by XRD, HAADF-STEM, XAFS, and 197Au Mössbauer, and these analyses revealed the formation of Au–Ni alloy components in the obtained catalysts. Au existed as Au nanoparticles together with Au–Ni alloy components in Au–Ni-1 prepared from Au/NiO by H2 treatment. When Au(OH)3–Ni(OH)2–NiCO3 was treated in a flow of H2 to produce Au–Ni-2, the formation of Au NPs was not clearly observed, thereby meaning that Au atoms were highly dispersed as a single atom and/or small clusters in the obtained catalysts. Moreover, most of the Au atoms were alloyed with Ni atoms for Au–Ni-2. The obtained Au–Ni-1 and Au–Ni-2 exhibited superior catalytic activities for the selective hydrogenolysis of benzylic alcohols into alkylbenzene derivatives in terms of reaction rates normalized by catalyst surface area. Accordingly, Au–Ni-1 and Au–Ni-2 recorded the reaction rates of 4.79 and 9.79 mmol L−1 h−1 m−2, respectively. These values were greater than that obtained for Raney Ni (0.14 mmol L−1 h−1 m−2). In addition, Au–Ni-2, which contains higher Au–Ni alloy content, showed greater reaction rates when compared to Au–Ni-1. Since Au/TiO2 showed poor catalytic activity for the hydrogenolysis, Au–Ni alloy enhanced the catalytic activities of Ni(0).Gold-nickel bimetallic catalysts were prepared from Au/NiO and Au(OH)3—Ni(OH)2—NiCO3 coprecipitates which showed exelent catalytic activities and selectivities for the hydrogenolysis of benzylic alcohols into alkylbenzene derivatives.Download high-res image (67KB)Download full-size image

•Transformation of terminal alkenes into allylic acetates over Pd/TiO2•An oxidation process using molecular oxygen as the sole oxidant•Achieving of excellent linear product selectivity and good catalyst recyclability•Positively charged Pd NPs on TiO2 promoted the reaction•The products are formed through the π-allyl-Pd intermediateA method for synthesizing linear allylic acetates from terminal alkenes over TiO2 supported Pd nanoparticles (NPs) has been developed, in which O2 serves as the sole oxidant. Good catalytic activity was performed when using allylbenzene as a substrate and the catalyst can be reused at least five times without activity losing. The catalytic system has a broad substrate scope including transformation of 1,3-butadiene into 1,4-diacetoxy-2-butene, which is an important industrial intermediate for production of 1,4-butanediol. In contrast to previous reports that the Pd-catalyzed allylic acetoxylation is generally promoted by PdII species, the XAFS measurements suggest that this reaction is catalyzed over Pd0 NPs. Additionally, XPS analysis of the catalyst confirms the interaction between Pd and TiO2, which probably promote the initial catalytic procedure.

Fischer-Tropsch synthesis (FTS) over unsupported coprecipitated cobalt catalysts in n-decane in a batch slurry phase reactor by adding water vapor (H2O/CO = 0.12 in molar ratio) prior to reaction has been studied. The addition of water vapor exhibits a marked effect on the product selectivity. In the absence of water, the carbon number distribution of FT products follows the classical Anderson-Schulz-Flory (ASF) pattern resulting in a low selectivity (32%) in the desired C10+ hydrocarbons. In contrast, with the promotion of water vapor, the formation of heavy products is appreciably increased up to 87.3% in C10+ hydrocarbons so that the selectivity in the range of C8–C30 increases obviously along with an increase in carbon number (n), which leads to a substantial deviation from ASF pattern. The effect of water is explained by suppressing secondary hydrogenation of 1-olefins and facilitating their readsorption and chain growth.Graphical abstractFischer-Tropsch synthesis (FTS) always exhibits Anderson-Schulz-Flory (ASF) pattern in the carbon number distribution at conventional reaction conditions, which limits the selective synthesis of desired middle distillates and wax. In our study, the addition of small amount of water into a batch slurry phase reactor gives a marked effect on the carbon number distribution so that the selectivity in the range of C8–C30 increases obviously along with an increase in carbon number (n), which leads to a substantial deviation from ASF pattern (78.6% in C11+ hydrocarbons). In contrast, in the absence of water, the carbon number distribution of FT products follows the classical Anderson-Schulz-Flory (ASF) pattern (28.3% in C11+ hydrocarbons). The effect of water is explained by suppressing secondary hydrogenation of 1-olefins and facilitating their readsorption and chain growth.Download high-res image (181KB)Download full-size imageHighlights► Fischer-Tropsch synthesis (FTS) is carried out in a batch slurry phase reactor. ► Water addition suppresses the hydrogenation of in situ 1-olefins. ► In situ 1-olefins are efficiently utilized for secondary chain growth. ► Water addition leads to a remarkable anti-ASF distribution. ► Hydrogenolysis of the FT hydrocarbons is a reversible process to FTS.

The intermolecular hydroaminomethylation and the intramolecular cyclocarbonylation efficiently proceeded on cobalt oxide supported gold nanoparticles. The intermolecular reaction employing terminal olefins and N-isopropylaniline afforded hydroaminomethylated products as a mixture of regioisomers via a common reaction path consisting of hydroformylation, imine formation, and hydrogenation. In contrast, indolinone derivatives were exclusively obtained in the case of 2-alkenylanilines based on the intramolecular cyclocarbonylation mechanism. Both of these reactions were catalyzed by cobalt species derived from cobalt oxide. The active cobalt species were formed via reduction of the oxide support promoted by deposited gold nanoparticles. Characterization of the catalysts before and after the reaction was also performed.

Transformation of cyclohexanones to phenols and aryl ethers over supported Pd catalysts using molecular oxygen as the sole oxidant is developed. Several metal oxide supported Pd catalysts were used to activate the C–H bond in cyclohexanones to produce cyclohexenones and phenols through oxidation. Although the selectivity of cyclohexenones was difficult to control, phenols were obtained in excellent yield with a broad substrate scope. A novel catalytic system, using ZrO2 supported Pd(OH)2, was proposed for the synthesis of aryl ethers, and the products were obtained in moderate to excellent yields. Orthoesters, such as trimethyl orthoformate (TMOF), triethyl orthoformate (TEOF), and triisopropyl orthoformate (TIPOF), enabled nucleophilic addition and elimination after activation of cyclohexanones over a Pd catalyst to produce the corresponding aryl ethers. TIPOF was also used as the dehydrating reagent to promote the reaction of cyclohexanones with alcohols for the preparation of versatile aryl ethers.