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6. Ultra-stable and highly reactive colloidal gold nanoparticle catalysts protected using multi-dentate metal oxide nanoclusters

Author

Xia, Kang, primary, Yatabe, Takafumi, additional, Yonesato, Kentaro, additional, Kikkawa, Soichi, additional, Yamazoe, Seiji, additional, Nakata, Ayako, additional, Ishikawa, Ryo, additional, Shibata, Naoya, additional, Ikuhara, Yuichi, additional, Yamaguchi, Kazuya, additional, and Suzuki, Kosuke, additional more...

Published
2024
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9. Multidentate polyoxometalate modification of metal nanoparticles with tunable electronic states.

Author

Xia, Kang, Yatabe, Takafumi, Yamaguchi, Kazuya, and Suzuki, Kosuke

Subjects
*METAL nanoparticles, *COOPERATIVE binding (Biochemistry), *PLATINUM nanoparticles, *CATALYTIC activity, *NANOPARTICLES
Abstract

To respond to the increasing demands for practical applications, stabilization and property modulation of metal nanoparticles have emerged as a key research subject. Herein, we present a viable protocol for preparing small metal nanoparticles (<5 nm; Ag, Pd, Pt, and Ru) via multidentate polyoxometalate (POM, [SiW9O34]10−) modification. In addition to enhancing stability, the POMs can modulate the electronic states of metal nanoparticles. Moreover, immobilization of the POM-modified metal nanoparticles on solid supports enables further tuning of the electronic states via a cooperative effect between the POMs and the supports without altering the particle size. Notably, POM-modified Pd nanoparticles on carbon support exhibited superior catalytic activity and selectivity in hydrogenation reactions in comparison with the catalyst without the POM modification. [ABSTRACT FROM AUTHOR] more...

Published
2024
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17. Direct thioether metathesis enabled by in situformed Pd nanocluster catalystsElectronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d3cy01563g

Author

Matsuyama, Takehiro, Yatabe, Takafumi, Yabe, Tomohiro, and Yamaguchi, Kazuya

Abstract

Thioether metathesis has been noted as a complementary thioether synthesis methodology with cross-coupling reactions, which can be applied to late-stage diversification. However, despite its utility, versatile direct C–S/C–S cross-metathesis of thioethers has not been previously reported. Herein, direct catalytic metathesis of various thioethers was enabled by Pd acetate and tricyclohexylphosphine precursors with no additives, affording unsymmetrical thioethers. Detailed characterization and control experiments confirmed that Pd(0) nanocluster homogeneous catalysts formed in situare the actual active species enabling this versatile direct transformation. This work will pave the way for novel organic molecular transformations driven by metal nanocluster catalysts. more...

Published
2024
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19. Mechanistic study of C-H bond activation by O-2 on negatively charged Au clusters : alpha,beta-dehydrogenation of 1-methyl-4-piperidone by supported Au catalysts dagger

Author

Miyazaki, Ray, Jin, Xiongjie, Yoshii, Daichi, Yatabe, Takafumi, Yabe, Tomohiro, Mizuno, Noritaka, Yamaguchi, Kazuya, and Hasegawa, Jun-ya

Abstract

Au nanoparticles supported on the manganese oxide octahedral molecular sieve OMS-2 can efficiently catalyze alpha,beta-dehydrogenation of beta-N-substituted saturated ketones using O-2 as the terminal oxidant. However, despite the utility of this reaction, the active sites and the reaction mechanism remain unclear. Here, the reaction mechanism for the Au/OMS-2-catalyzed aerobic alpha,beta-dehydrogenation of 1-methyl-4-piperidone was investigated mainly by using density functional theory (DFT) calculations. From control experiments under various reaction conditions, we found that O-2 plays an important role in the alpha,beta-dehydrogenation over Au nanoparticles. Thus, we attempted to clarify the mechanism for the alpha,beta-dehydrogenation of 1-methyl-4-piperidone on Au nanoparticle catalysts by DFT calculations using Au cluster models. The reaction was found to cleave the C-H-alpha and C-H-beta bonds in that order. An O-2 molecule adsorbed on the negatively charged Au cluster caused by charge transfer from OMS-2 was found to be sufficiently activated to abstract the H-alpha atom in the 1-methyl-4-piperidone substrate. This indirect H-alpha abstraction by the activated O-2 was energetically more favorable than direct H-alpha abstraction by the Au cluster. The subsequent H-beta abstraction was found to be promoted by adsorbed oxygen species (i.e., HOO, OH, and O) formed after the H-alpha abstraction. The reaction mechanism proposed in this study provides general insight into the aerobic C-H bond activation by supported Au catalysts. more...

Published
2021

29. Regiospecific α-methylene functionalisation of tertiary amines with alkynes via Au-catalysed concerted one-proton/two-electron transfer to O2.

Author

Yatabe, Takafumi and Yamaguchi, Kazuya

Abstract

Regioselective transformations of tertiary amines, which are ubiquitously present in natural products and drugs, are important for the development of novel medicines. In particular, the oxidative α-C–H functionalisation of tertiary amines with nucleophiles via iminium cations is a promising approach because, theoretically, there is almost no limit to the type of amine and functionalisation. However, most of the reports on oxidative α-C–H functionalisations are limited to α-methyl-selective or non-selective reactions, despite the frequent appearance of α-methylene-substituted amines in pharmaceutical fields. Herein, we develop an unusual oxidative regiospecific α-methylene functionalisation of structurally diverse tertiary amines with alkynes to synthesise various propargylic amines using a catalyst comprising Zn salts and hydroxyapatite-supported Au nanoparticles. Thorough experimental investigations suggest that the unusual α-methylene regiospecificity is probably due to a concerted one-proton/two-electron transfer from amines to O2 on the Au nanoparticle catalyst, which paves the way to other α-methylene-specific functionalisations.The selective α-methylene functionalization of tertiary amines is challenging. Here, the authors report the gold nanoparticles-catalyzed α-methylene alkynylation of tertiary amines via concerted one-proton/two-electron transfer to O2. [ABSTRACT FROM AUTHOR] more...

Published
2022
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35. Nanostructured Manganese Oxides within a Ring‐Shaped Polyoxometalate Exhibiting Unusual Oxidation Catalysis.

Author

Sato, Kai, Yonesato, Kentaro, Yatabe, Takafumi, Yamaguchi, Kazuya, and Suzuki, Kosuke

Subjects
MANGANESE oxides, CATALYSIS, CATALYTIC activity, HOMOGENEOUS catalysis, METALLIC oxides, MANGANESE catalysts
Abstract

Nanosized manganese oxides have recently received considerable attention for their synthesis, structures, and potential applications. Although various synthetic methods have been developed, precise synthesis of novel nanostructured manganese oxides are still challenging. In this study, using a structurally defined nanosized cavity inside a ring‐shaped polyoxometalate, we succeeded in synthesizing two types of discrete 18 and 20 nuclear nanostructured manganese oxides, Mn18 and Mn20, respectively. In particular, Mn18 showed much higher catalytic activity than other manganese oxides for the oxygenation of alkylarenes including electron‐deficient ones, and the reaction proceeded through a unique reaction mechanism due to its unusual manganese oxide structure. [ABSTRACT FROM AUTHOR] more...

Published
2022
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46. Mechanistic study of C–H bond activation by O2on negatively charged Au clusters: α,β-dehydrogenation of 1-methyl-4-piperidone by supported Au catalystsElectronic supplementary information (ESI) available: Surface structure of OMS-2, adsorption structures of 1-methyl-4-piperidone and O2on the Au20models, C–Hβbond activation of 1-methyl-4-piperidone in the first C–H bond cleavage step, comparison of calculation settings, definition of the relative potential energies for the second C–H bond cleavage pathways, optimized structures for C–Hαbond activation by the adsorbed O and OH species, Cartesian coordinates of optimized structures throughout the catalytic cycle, and results of control experiments for the α,β-dehydrogenation of 1-methyl-4-piperidone by the Au/OMS-2, Au/Al2O3, and Au/C catalysts. See DOI: 10.1039/d1cy00178g

Author

Miyazaki, Ray, Jin, Xiongjie, Yoshii, Daichi, Yatabe, Takafumi, Yabe, Tomohiro, Mizuno, Noritaka, Yamaguchi, Kazuya, and Hasegawa, Jun-ya

Abstract

Au nanoparticles supported on the manganese oxide octahedral molecular sieve OMS-2 can efficiently catalyze α,β-dehydrogenation of β-N-substituted saturated ketones using O2as the terminal oxidant. However, despite the utility of this reaction, the active sites and the reaction mechanism remain unclear. Here, the reaction mechanism for the Au/OMS-2-catalyzed aerobic α,β-dehydrogenation of 1-methyl-4-piperidone was investigated mainly by using density functional theory (DFT) calculations. From control experiments under various reaction conditions, we found that O2plays an important role in the α,β-dehydrogenation over Au nanoparticles. Thus, we attempted to clarify the mechanism for the α,β-dehydrogenation of 1-methyl-4-piperidone on Au nanoparticle catalysts by DFT calculations using Au cluster models. The reaction was found to cleave the C–Hαand C–Hβbonds in that order. An O2molecule adsorbed on the negatively charged Au cluster caused by charge transfer from OMS-2 was found to be sufficiently activated to abstract the Hαatom in the 1-methyl-4-piperidone substrate. This indirect Hαabstraction by the activated O2was energetically more favorable than direct Hαabstraction by the Au cluster. The subsequent Hβabstraction was found to be promoted by adsorbed oxygen species (i.e., HOO, OH, and O) formed after the Hαabstraction. The reaction mechanism proposed in this study provides general insight into the aerobic C–H bond activation by supported Au catalysts. more...

Published
2021
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47. Selective Synthesis of Primary Anilines from NH3 and Cyclohexanones by Utilizing Preferential Adsorption of Styrene on the Pd Nanoparticle Surface.

Author

Koizumi, Yu, Jin, Xiongjie, Yatabe, Takafumi, Miyazaki, Ray, Hasegawa, Jun‐ya, Nozaki, Kyoko, Mizuno, Noritaka, and Yamaguchi, Kazuya

Subjects
CYCLOHEXANONES, ANILINE, STYRENE, HETEROGENEOUS catalysis, ADSORPTION (Chemistry), HYDROXYAPATITE
Abstract

Dehydrogenative aromatization is one of the attractive alternative methods for directly synthesizing primary anilines from NH3 and cyclohexanones. However, the selective synthesis of primary anilines is quite difficult because the desired primary aniline products and the cyclohexanone substrates readily undergo condensation affording the corresponding imines (i.e. N‐cyclohexylidene‐anilines), followed by hydrogenation to produce N‐cyclohexylanilines as the major products. In this study, primary anilines were selectively synthesized in the presence of supported Pd nanoparticle catalysts (e.g. Pd/HAP, HAP=hydroxyapatite, Ca10(PO4)6(OH)2) by utilizing competitive adsorption unique to heterogeneous catalysis; in other words, when styrene was used as a hydrogen acceptor, which preferentially adsorbs on the Pd nanoparticle surface in the presence of N‐cyclohexylidene‐anilines, various structurally diverse primary anilines were selectively synthesized from readily accessible NH3 and cyclohexanones. The Pd/HAP catalyst was reused several times though its catalytic performance gradually declined. [ABSTRACT FROM AUTHOR] more...

Published
2019
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