後期遷移金属触媒による酸素を酸化剤とした新規脱水素型クロスカップリング反応の開発

学位の種別: 課程博士審査委員会委員 : (主査)東京大学教授 石井 和之, 東京大学教授 小林 修, 東京大学教授 野崎 京子, 東京大学准教授 山口 和也, 中央大学准教授 山下 誠University of Tokyo(東京大学

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

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

Copper-Catalyzed Oxidative Cross-Coupling of <i>H</i>‑Phosphonates and Amides to <i>N</i>‑Acylphosphoramidates

A simple combination of copper(II) acetate (Cu(OAc)₂) and an appropriate base could promote oxidative cross-coupling of <i>H</i>-phosphonates and amides using air as a terminal oxidant. The substrate scope was broad with respect to both dialkyl <i>H</i>-phosphonates and nitrogen nucleophiles (including oxazolidinone, lactam, pyrrolidinone, urea, indole, and sulfonamide derivatives), giving the corresponding P–N coupling products in moderate to high yields

Hydrogen-induced formation of surface acid sites on Pt/Al(PO3)3 enables remarkably efficient hydrogenolysis of C−O bonds in alcohols and ethers

The hydrogenolysis of oxygenates such as alcohols and ethers is central to the biomass valorization and also a valuable transformation in organic synthesis. However, there is lack of a mild and efficient catalyst system that is applicable to a wide range of alcohols and ethers. Here, we report an aluminum metaphosphate-supported Pt nanoparticles for the hydrogenolysis of a wide variety of primary, secondary, and tertiary alkyl and benzylic alcohols, and dialkyl, aryl alkyl, and diaryl ethers, including biomass-derived furanic compounds, under mild conditions (0.1–1 atm of H2, as low as 70 °C). Mechanistic studies suggested that H2 induces formation of the surface Brønsted acid sites via its cleavage by supported Pt nanoparticles. Accordingly, the high efficiency and the wide applicability of the catalyst system can be attributed to the cooperative activation and cleavage of C–O bonds of alcohols and ethers by the hydrogen-induced Brønsted acid sites and Lewis acidic Al sites on Al(PO3)3 surface. The high efficiency of the catalyst imply its potential application in energy efficient biomass valorization or fine chemical synthesis

Unusual Olefinic C–H Functionalization of Simple Chalcones toward Aurones Enabled by the Rational Design of a Function-Integrated Heterogeneous Catalyst

Flavonoids, which are ubiquitous plant secondary metabolites obtained from chalcones, mostly possess 6-membered C-rings derived from 6-<i>endo-trig</i> cyclization of chalcones. However, aurones, which are a class of flavonoids that rarely occur naturally, possess unusual 5-membered C-rings biosynthesized from chalcones by mainly performing B-ring oxidation. Therefore, the chemical catalytic transformation from simple chalcones into aurones is attractive, because it overcomes the drawback of known limited enzyme catalysis. The catalytic transformation, however, has not yet been reported because of the preferential 6-membered ring formation as with the biosynthesis and the need for rare intramolecular olefinic C–H functionalization. Here, we developed the catalytic olefinic C–H functionalization of simple chalcones toward various aurones enabled by the rational design of a function-integrated heterogeneous catalysta Pd-on-Au bimetallic nanoparticle catalyst supported on CeO₂using O₂ in air as the sole oxidant without any additives. In this system, the four conditions that were required for the challenging transformation toward aurones were achieved by the respective components of the catalyst: (a) a supported Pd catalyst: a catalyst for the olefinic C–H functionalization of chalcones toward aurones, (b) an Au promoter: an improvement in the catalytic activity by stabilizing Pd(0), (c) a CeO₂ support: the inhibition of the 6-<i>endo-trig</i> cyclization utilizing the adsorption of chalcones, and (d) a Pd-on-Au structure: the inhibition of Au-catalyzed flavone synthesis. This catalytic transformation will promote not only the pharmaceutical study of aurones but also the rational design of a heterogeneous catalyst for the development of organic reactions that are not yet realized by homogeneous catalysts or biocatalyst

Sound absorption performance based on auxetic microstructure model: A parametric study

With the increasing prominence and complexity of environmental noise problems, there is an urgent need for novel acoustic materials to meet noise reduction requirements. In this paper, two auxetic microstructures and three typical lattice microstructures are established, and a microscopic-macroscopic acoustic performance study scheme is established through the Johnson-Champoux-Allard-Pride-Lafarge (JCAPL) model. Auxetic-BCC porous materials have lower acoustic resistance and reactance amplitudes than many typical porous materials through experimental verification and comparative analysis of numerical calculations. The porous material's thickness and the backing cavity's thickness have similar effects on sound absorption performance when controlling a single change in structural parameters, and there is an optimum thickness. As acoustic resistance and reactance are dominant at low and high frequencies, respectively, noise reduction is better at low (high) frequencies than at minor (large) porosity, and the porosity of 76.4%–82.0% has the best sound absorption effect. Changes in prism length of materials with high porosity are more sensitive than those with low porosity, so the prism length with porosity of 76.4%, 79.0%, and 82.6% shall be designed to be less than 1.1 mm, 0.9 mm, 0.8 mm, respectively. This study provides theoretical guidance for designing multifunctional porous materials in extreme environments

Selective Synthesis of Primary Anilines from Cyclohexanone Oximes by the Concerted Catalysis of a Mg–Al Layered Double Hydroxide Supported Pd Catalyst

Although the selective conversion of cyclohexanone oximes to primary anilines would be a good complement to the classical synthetic methods for primary anilines, which utilize arenes as the starting materials, there have been no general and efficient methods for the conversion of cyclohexanone oximes to primary anilines until now. In this study, we have successfully realized the efficient conversion of cyclohexanone oximes to primary anilines by utilizing a Mg–Al layered double hydroxide supported Pd catalyst (Pd­(OH)_<i>x</i>/LDH) under ligand-, additive-, and hydrogen-acceptor-free conditions. The substrate scope was very broad with respect to both cyclohexanone oximes and cyclohexenone oximes, which gave the corresponding primary anilines in high yields with high selectivities (17 examples, 75% to >99% yields). The reaction could be scaled up (gram-scale) with a reduced amount of the catalyst (0.2 mol %). Furthermore, the one-pot synthesis of primary anilines directly from cyclohexanones and hydroxylamine was also successful (five examples, 66–99% yields). The catalysis was intrinsically heterogeneous, and the catalyst could be reused for the conversion of cyclohexanone oxime to aniline at least five times with keeping its high catalytic performance. Kinetic studies and several control experiments showed that the high activity and selectivity of the present catalyst system were attributed to the concerted catalysis of the basic LDH support and the active Pd species on LDH. The present transformation of cyclohexanone oximes to primary anilines proceeds through a dehydration/dehydrogenation sequence, and herein the plausible reaction mechanism is proposed on the basis of several pieces of experimental evidence