Tamao Ishida

Synergistic Catalysis of Au@Ag Core—Shell Nanoparticles Stabilized on Metal—Organic Framework

For the first time, this work presents Au@Ag core-shell nanoparticles (NPs) immobilized on a metal-organic framework (MOF) by a sequential deposition-reduction method. The small-size Au@Ag NPs reveal the restriction effects of the pore/surface structure in the MOF. The modulation of the Au/Ag ratio can tune the composition and a reversed Au/Ag deposition sequence changes the structure of Au-Ag NPs, while a posttreatment process transforms the core-shell NPs to a AuAg alloy. Catalytic studies show a strong bimetallic synergistic effect of core-shell structured Au@Ag NPs, which have much higher catalytic activities than alloy and monometallic NPs.

Deposition of Gold Clusters on Porous Coordination Polymers by Solid Grinding and Their Catalytic Activity in Aerobic Oxidation of Alcohols

Gold has turned out to be one of the most attractive elements in catalysis research since the discovery of CO oxidation at 70 8C over Au nanoparticles (NPs) supported on base metal oxides. During the last decade, Au NPs supported on metal oxides and activated carbons (AC) have been widely studied for liquid phase reactions. In liquid phase reactions, catalytic performance of Au particles is mainly defined by two major factors: i) the nature of supports and ii) the size of Au particles. In particular, the size of 2 nm appears to be a critical point, where the Au particles dramatically change their catalytic and physicochemical properties. However, the conventional deposition–precipitation method is not applicable to AC due to the acidic nature of AC. Mixing Au colloids with AC could hardly give Au clusters with a diameter smaller than 2 nm. A latest trend in the selection of supports is the use of organic polymers. Recently, some organic polymers were found to be effective to stabilize colloidal Au in a cluster size, which showed high catalytic activity for aerobic oxidation of alcohols at room temperature. However, a constraint is that sophisticated synthetic techniques are usually required to obtain Au clusters. On the other hand, porous coordination polymers (PCPs) consisting of metal ions and organic ligands with highly regular nanometer-sized cavities or channels are an emerging class of porous materials. They are expected to be efficient supports for metal clusters to control size and shape by means of their cavities. In addition, PCPs have a wide variety of porous structures, various kinds of components, and surface properties which would lead to tailor-made catalysts for the desired reactions. Thus, investigations of the preparation methods for PCP supported Au clusters and the support effect of PCPs would offer a new frontier in catalysis by Au. Fischer and co-workers have reported the preparation of Pd, Cu, Ru clusters, and Au NPs stabilized by Zncontaining PCP, MOF-5 ([Zn4O ACHTUNGTRENNUNG(bdc)3]n (bdc=benzene-1,4dicarboxylate) by chemical vapour deposition (CVD). Although Au particles could be hardly deposited in cluster size, they were obtained as NPs in the range of 5 to 20 nm on MOF-5 due to weak interaction. 12] Therefore, the generation of Au clusters that fit in and/or on the cavities of PCPs is still a challenging research target. Herein we report a very simple but the most effective method for the direct deposition of Au clusters onto several kinds of PCPs including MOF-5 by solid grinding with a volatile organogold complex without using organic solvents. We also investigated their catalytic properties for the liquid phase alcohol oxidation with molecular oxygen. To the best of our knowledge, catalysis of PCP supported Au clusters in liquid phase has not yet been studied. The PCP supports used were one-dimensionally channelled PCPs such as CPL-1 ([Cu2ACHTUNGTRENNUNG(pzdc)2 ACHTUNGTRENNUNG(pyz)]n, pzdc=pyrazine-2,3-dicarboxylate, pyz=pyrazine), CPL-2 ([Cu2ACHTUNGTRENNUNG(pzdc)2ACHTUNGTRENNUNG(bpy)]n, bpy=4,4’-bipyridine), [14] Al-MIL53 ([Al(OH) ACHTUNGTRENNUNG(bdc)]n) [15] with pores of 4 @6, 6 @ 8, 8.5 @8.5 A, respectively, and three-dimensional PCPs such as MOF-5 and Cu-BTC ([Cu3ACHTUNGTRENNUNG(btc)2]n (btc=benzene-1,3,5-tricarboxylate) [16] with pores of 15 @ 15 and 11 @11 A, respectively. Volatile organogold complex, Me2AuACHTUNGTRENNUNG(acac) (acac= acetylacetonate) and PCPs were ground in an agate mortar in air for 20 min at room temperature. Then the mixture was treated in a stream of 10 vol% H2 in N2 at 120 8C for 2 h to obtain Au/ [a] Dr. T. Ishida, M. Nagaoka, Prof. Dr. M. Haruta Department of Applied Chemistry Graduate School of Urban Environmental Sciences Tokyo Metropolitan University, 1-1 Minami-osawa Hachioji, Tokyo 192-0397 (Japan) Fax: (+81) 42-677-2851 E-mail : haruta-masatake@center.tmu.ac.jp [b] Dr. T. Ishida, Dr. T. Akita, Prof. Dr. M. Haruta Japan Science and Technology Agency (JST) CREST, 4-1-8 Hon-cho, Kawaguchi Saitama 322-0012 (Japan) [c] Dr. T. Akita Research Institute for Ubiquitous Energy Devices National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka Ikeda, Osaka 563-8577 (Japan) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200800980.

One-Pot Synthesis of Indoles and Aniline Derivatives from Nitroarenes under Hydrogenation Condition with Supported Gold Nanoparticles

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 Fe(2)O(3). Nitro group selective hydrogenations and successive reactions were efficiently catalyzed under the conditions.

One-potN-alkylation of primary amines to secondary amines by gold clusters supported on porous coordination polymers

Gold clusters and nanoparticles were deposited on the three kinds of porous coordination polymers (PCP5), MOF-5, CPL-2, and AI-MIL53 by the solid grinding method. The size of Au particles depended on the kinds of PCPs and increased in the order of AI-MIL53 < CPL-2 < MOF-5. The mean diameter of Au particles supported on AI-MIL53 was estimated to be 1.6 nm by HAADFSTEM. Such small Au clusters on AI-MIL53 can catalyze one-pot synthesis of secondary amines from primary amines by sequential oxidation/hydrogenation owing to the remarkable improvement of hydrogenation efficiency of imine. Gold clusters deposited on AI-MIL53 can also promoteN-alkylation of amine with alcohol to form a secondary amine under N2 atmosphere without using O2 and H2.

Direct deposition of gold nanoparticles onto polymer beads and glucose oxidation with H2O2.

Gold nanoparticles (Au NPs) were deposited directly from aqueous solution of diethylenediaminegold(III) complex onto polymer beads commercially available, such as poly(methyl methacrylate) (PMMA), polystyrene (PS), and polyaniline (PANI) without surface modification. The dropwise addition of NaBH4 to reduce Au(III) was found to be very effective to obtain small Au0 NPs with a narrow size distribution except for PANI. The catalytic performance of Au NPs deposited on polymer beads for H2O2 decomposition and glucose oxidation with H2O2 were more significantly affected by the kinds of polymer supports than by the size of Au NPs. The equimolar oxidation of glucose with H2O2 could be operated by controlling the decomposition rate of H2O2 over Au/PMMA.

N‐Formylation of Amines via the Aerobic Oxidation of Methanol over Supported Gold Nanoparticles

Dress code: formyl. Gold nanoparticles supported on NiO catalyze the one-pot N-formylation of amines with methanol and molecular oxygen to produce formamide at a selectivity of 90 %. This process generates methyl formate in situ, followed by reaction with amines.

Base‐Free Direct Oxidation of 1‐Octanol to Octanoic Acid and its Octyl Ester over Supported Gold Catalysts

The choice of a suitable support for gold nanoparticles (Au NPs) enabled the direct oxidation of unreactive aliphatic alcohol, 1-octanol, to octanoic acid and octyl octanoate in the absence of a base. Under optimized conditions, Au NPs supported on NiO (Au/NiO) exhibited remarkably high catalytic activities and excellent selectivities to octanoic acid (e.g., 97 %) at full conversion. In contrast to Au/NiO, Au/CeO₂ selectively produced octyl octanoate as a major product in a base-free aqueous solution with a maximum selectivity of 82 % under optimized conditions.

Hydrolytic enantioselective protonation of cyclic dienyl esters and a β-diketone with chiral phase-transfer catalysts

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).

Advances in Gold Catalysis and Understanding the Catalytic Mechanism

When gold is deposited as nanoparticles (NPs) with mean diameters of 2-5 nm or clusters with mean diameters below 2 nm onto a variety of supports such as metal oxides, carbons, polymers, etc., the supported Au NPs exhibit unique catalytic properties, while bulk Au is almost inert as a catalyst. A lot of research works indicate that the key factors of the catalysis by supported Au NPs are the selection of the supports, the control of the Au NP size, the shape of the Au NPs, and the strong junction between Au NPs and the supports, because the perimeter zone around Au NPs acts as the active site for many reactions. In order to elucidate the origin of catalysis by supported Au NPs, the interplay between physicochemical analysis, computational studies, and rational experiments for catalysis by supported Au NPs is becoming more and more important. This article summarizes our experiences and progress in such interplay.

Aerobic oxidation of cyclohexanones to phenols and aryl ethers over supported Pd catalysts

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.