Hiroyuki Miyamura

Powerful Amide Synthesis from Alcohols and Amines under Aerobic Conditions Catalyzed by Gold or Gold/Iron, -Nickel or -Cobalt Nanoparticles

Considering the importance of the development of powerful green catalysts and the omnipresence of amide bonds in natural and synthetic compounds, we report here on reactions between alcohols and amines for amide bond formation in which heterogeneous gold and gold/iron, -nickel, or -cobalt nanoparticles are used as catalysts and molecular oxygen is used as terminal oxidant. Two catalysts show excellent activity and selectivity, depending on the type of alcohols used. A wide variety of alcohols and amines, including aqueous ammonia and amino acids, can be used for the amide synthesis. Furthermore, the catalysts can be recovered and reused several times without loss of activity.

Remarkable effect of bimetallic nanocluster catalysts for aerobic oxidation of alcohols: combining metals changes the activities and the reaction pathways to aldehydes/carboxylic acids or esters.

Selective oxidation of alcohols catalyzed by novel carbon-stabilized polymer-incarcerated bimetallic nanocluster catalysts using molecular oxygen has been developed. The reactivity and the selectivity were strongly dependent on the combination of metals and solvent systems; aldehydes and ketones were obtained by the gold/platinum catalyst in benzotrifluoride, and esters were formed by the gold/palladium catalyst in methanol. To the best of our knowledge, this is the first example that the reaction pathway has been changed dramatically in gold catalysis by combining with a second metal. The differences in the activity and the selectivity are considered to be derived from the difference in the structure of the bimetallic clusters.

Aerobic oxidative esterification of alcohols catalyzed by polymer-incarcerated gold nanoclusters under ambient conditions

Environmentally benign aerobic oxidation of alcohols to methyl esters catalyzed by polymer-incarcerated gold nanoclusters (PI-Au) was developed and reactions proceeded under very mild conditions. The catalyst could be recovered by simple operations without significant loss of activity.

Polymer-Incarcerated Gold−Palladium Nanoclusters with Boron on Carbon: A Mild and Efficient Catalyst for the Sequential Aerobic Oxidation−Michael Addition of 1,3-Dicarbonyl Compounds to Allylic Alcohols

We have developed a polymer-incarcerated bimetallic Au-Pd nanocluster and boron as a catalyst for the sequential oxidation-addition reaction of 1,3-dicarbonyl compounds with allylic alcohols. The desired tandem reaction products were obtained in good to excellent yields under mild conditions with broad substrate scope. In the course of our studies, we discovered that the excess reducing agent, sodium borohydride, reacts with the polymer backbone to generate an immobilized tetravalent boron catalyst for the Michael reaction. In addition, we found bimetallic Au-Pd nanoclusters to be particularly effective for the aerobic oxidation of allylic alcohols under base- and water-free conditions. The ability to conduct the reaction under relatively neutral and anhydrous conditions proved to be key in maintaining good catalyst activity during recovery and reuse of the catalyst. Structural characterization (STEM, EDS, SEM, and N(2) absorption/desorption isotherm) of the newly prepared PI/CB-Au/Pd/B was performed and compared to PI/CB-Au/Pd. We found that while boron was important for the Michael addition reaction, it was found to alter the structural profile of the polymer-carbon black composite material to negatively affect the allylic oxidation reaction.

Polymer-incarcerated metal(0) cluster catalysts.

Polymer-incarcerated metal(0) nanocluster catalysts were developed based on two techniques: microencapsulation and cross-linking. Pd, Au, Pt, and bimetallic nanoclusters could be efficiently immobilized on polymers containing benzene rings keeping subnanometer- to nanometer-size clusters. Catalysts could be used for redox reactions using molecular hydrogen and oxygen, and could be reused without aggregation of nanoclusters and leaching of metals. Modification of polymers and addition of second inorganic supports sometimes increased their reactivity.

Rate‐Acceleration in Gold‐Nanocluster‐Catalyzed Aerobic Oxidative Esterification Using 1,2‐ and 1,3‐Diols and Their Derivatives

Aerobic oxidation of aldehydes to 1,2- and 1,3-diol monoesters was catalyzed by polymer-incarcerated gold nanoclusters under ambient conditions. The esterification proceeded much faster with 1,2- and 1,3-diols and their derivatives rather than with methanol.

Multiphase Flow Systems for Selective Aerobic Oxidation of Alcohols Catalyzed by Bimetallic Nanoclusters

Au-Pt and Au-Pd bimetallic nanoclusters that catalyzed the aerobic oxidation of alcohols during a once-through pass through gas-liquid-liquid-solid flow systems were developed. Alcohols were converted to aldehydes and ketones in benzotrifluoride (BTF)/water media by Au-Pt catalyst or to the corresponding methyl esters in methanol/water media by Au-Pd catalyst. The flow systems were superior to the batch systems in terms of both yield and selectivity.

Copper-catalyzed, aerobic oxidative cross-coupling of alkynes with arylboronic acids: remarkable selectivity in 2,6-lutidine media.

Aerobic oxidative cross-coupling reactions between alkynes and boronic acids under mild conditions catalyzed by low loadings of a copper salt are reported. 2,6-Lutidine accelerated the reactions dramatically, and the desired coupling products were obtained in high yields with high selectivities.