Synthesis and Characterization of Dithia[3.3](2,6)pyridinophane-Containing Polymers: Application to the Palladium-Catalyzed Heck Reaction

We synthesized zigzag polymers consisting of dithia[3.3](2,6)pyridinophane units that were flipped rapidly as a result of syn-[anti]-syn isomerization. Pyridinophane units were fixed in the syn form by complexation with palladium, and the resulting polymer complex exhibited a high catalytic activity for the Heck coupling reaction

“In-water” Dehydration Reaction of an Aromatic Diol on an Inorganic Surface

The effect of a synthetic saponite surface on the “in-water” dehydration reaction of diol was examined using 4-formyl-1-methylquinolinium salt (MQu+) as a substrate. The equilibrium between aldehyde (MQu+-Aldehyde) and diol (MQu+-Diol) was affected by the surrounding environment. The equilibrium behavior was observed by 1H nuclear magnetic resonance (NMR) and UV–vis absorption measurements. Although MQu+ was completely in the form of MQu+-Diol in water, the equilibrium almost shifted to the MQu+-Aldehyde side when MQu+ was adsorbed on the saponite surface in water. In addition, the MQu+-Aldehyde ratio depended on the negative charge density of saponite. The factors that determine MQu+-Aldehyde: MQu+-Diol ratio were discussed from the thermodynamic analysis of the system. These data indicate that the electrostatic interaction between the charged saponite surface and MQu+ stabilized the aldehyde side enthalpically and destabilized it entropically. The major reason for these results is considered to be the difference in adsorption stabilization between MQu+-Aldehyde and MQu+-Diol on saponite surfaces

Effects of the Surface Charge Density of Clay Minerals on Surface-Fixation Induced Emission of Acridinium Derivatives

Surface-fixation induced emission is a fluorescence enhancement phenomenon, which is expressed when dye molecules satisfy a specific adsorption condition on the anionic clay surface. The photophysical behaviors of two types of cationic acridinium derivatives [10-methylacridinium perchlorate (Acr+) and 10-methyl-9-phenylacridinium perchlorate (PhAcr+)] on the synthetic saponites with different anionic charge densities were investigated. Under the suitable conditions, the fluorescence quantum yield (Φf) of PhAcr+ was enhanced 22.3 times by the complex formation with saponite compared to that in water without saponite. As the inter-negative charge distance of saponite increased from 1.04 to 1.54 nm, the Φf of PhAcr+ increased 1.25 times. In addition, the increase in the negative charge distance caused the increase in the integral value of the extinction coefficient and the radiative deactivation rate constant (kf) and the decrease in the nonradiative deactivation rate constant. It should be noted that the 2.3 times increase in kf is the highest among the reported values for the effect of clay. From these results, it was concluded that the photophysical properties of dyes can be modulated by changing the charge density of clay minerals

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

Structural Transformation of Azonia[5]helicene Photoproduct via Reaction Field Function of Layered Inorganic Material

In an attempt to generalize “on surface synthesis”, which has unique potential in the area of organic synthesis, the focus was placed on layered silicates having a highly flat surface. The photoreaction of (±)-13-bromo-6a-azonia[5]­helicene (AHHBr) and (±)-2-bromo-13-methyl-6a-azonia[5]­helicene (AHBrMe) in solution and within the layers was examined. In the case of AHBrMe, the photoproduct was different from that in solution. 1H nuclear magnetic resonance (NMR), Fourier transform-infrared spectroscopy (FT-IR), and electrospray ionization-mass spectrometry (ESI-MS) measurements revealed that the photoproduct obtained within the layers was a benzo-perylene molecule with a completely flat lactone structure (AL). This study is the first example of the successful conversion of a chemical reaction path due to the steric effect of the flat surface of layered silicate

Emission Enhancement of Anthracene Derivative Caused by a Dramatic Molecular Orbital Change on the Nanosheet Surface

The emission enhancement phenomenon on clay nanosheets is called surface-fixation-induced emission (S-FIE) and is similar to aggregation-induced emission, which has attracted the attention of many researchers. Both emission enhancement phenomena are primarily caused by the suppression of nonradiative deactivation. In this study, a new S-FIE molecule was synthesized and its basic photochemical behavior was investigated. The emission enhancement of the new molecule on the clay surface was induced by the suppression of nonradiative deactivation and acceleration of radiative deactivation. Density functional theory calculations indicated that the acceleration of radiative deactivation originated from the improvement in the spatial overlap between the two molecular orbitals related to the emission phenomenon and the increase in the Frank–Condon factor

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 Fe2O3. Nitro group selective hydrogenations and successive reactions were efficiently catalyzed under the 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)

The Development of the Regenerable Catalytic System in Selective Catalytic Oxidation of Ammonia with High N₂ Selectivity

Supported particulate noble-metal catalysts are widely used in industrial catalytic reactions. However, these metal species, whether in the form of nanoparticles or highly dispersed entities, tend to aggregate during reactions, leading to a reduced activity or selectivity. Addressing the frequent necessity for the replacement of industrial catalysts remains a significant challenge. Herein, we demonstrate the feasibility of the ‘regenerable catalytic system’ exemplified by selective catalytic oxidation of ammonia (NH3–SCO) employing Ag/Al2O3 catalysts. Results demonstrate that our highly dispersed Ag catalyst (Ag HD) maintains >90% N2 selectivity at 80% NH3 conversion and >80% N2 selectivity at 100% NH3 conversion after enduring 5 cycles of reducible aggregation and oxidative dispersion. Moreover, it consistently upholds over 98% N2 selectivity at 100% NH3 conversion after 10 cycles of Ar treatment. During the aggregation–dispersion process, the Ag HD catalyst intentionally aggregated into Ag nanoparticles (Ag NP) after H2 reduction and exhibited remarkable regenerable capabilities, returning to the Ag HD state after calcination in the air. This structural evolution was characterized through in situ transmission electron microscopy, atomically resolved high-angle annular dark-field scanning transmission electron microscopy, and X-ray absorption spectroscopy, revealing the on-site oxidative dispersion of Ag NP. Additionally, in situ diffuse reflectance infrared Fourier transform spectroscopy provided insights into the exceptional N2 selectivity on Ag HD catalysts, elucidating the critical role of NO+ intermediates. Our findings suggest a sustainable and cost-effective solution for various industry applications

The Development of the Regenerable Catalytic System in Selective Catalytic Oxidation of Ammonia with High N₂ Selectivity

Supported particulate noble-metal catalysts are widely used in industrial catalytic reactions. However, these metal species, whether in the form of nanoparticles or highly dispersed entities, tend to aggregate during reactions, leading to a reduced activity or selectivity. Addressing the frequent necessity for the replacement of industrial catalysts remains a significant challenge. Herein, we demonstrate the feasibility of the ‘regenerable catalytic system’ exemplified by selective catalytic oxidation of ammonia (NH3–SCO) employing Ag/Al2O3 catalysts. Results demonstrate that our highly dispersed Ag catalyst (Ag HD) maintains >90% N2 selectivity at 80% NH3 conversion and >80% N2 selectivity at 100% NH3 conversion after enduring 5 cycles of reducible aggregation and oxidative dispersion. Moreover, it consistently upholds over 98% N2 selectivity at 100% NH3 conversion after 10 cycles of Ar treatment. During the aggregation–dispersion process, the Ag HD catalyst intentionally aggregated into Ag nanoparticles (Ag NP) after H2 reduction and exhibited remarkable regenerable capabilities, returning to the Ag HD state after calcination in the air. This structural evolution was characterized through in situ transmission electron microscopy, atomically resolved high-angle annular dark-field scanning transmission electron microscopy, and X-ray absorption spectroscopy, revealing the on-site oxidative dispersion of Ag NP. Additionally, in situ diffuse reflectance infrared Fourier transform spectroscopy provided insights into the exceptional N2 selectivity on Ag HD catalysts, elucidating the critical role of NO+ intermediates. Our findings suggest a sustainable and cost-effective solution for various industry applications