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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

The introduction of pyridinic nitrogen (pyri-N) into carbon-based electrocatalysts for the oxygen reduction reaction is considered to create new active sites. Herein, the role of pyri-N in such catalysts was investigated from a mechanistic viewpoint using carbon black (CB)-supported pyri-N-containing molecules as model catalysts; the highest activity was observed for 1,10-phenanthroline/CB. X-ray photoemission spectroscopy showed that in acidic electrolytes, both pyri-N atoms of 1,10-phenanthroline could be protonated to form pyridinium ions (pyri-NH+). In O-2-saturated electrolytes, one of the pyri-NH+ species was reduced to pyri-NH upon the application of a potential; no such reduction was observed in N-2-saturated electrolytes. This behavior was ascribed to electrochemical reduction of pyri-NH+ occurring simultaneously with the thermal adsorption of O-2, as supported by DFT calculations. According to these calculations, the coupled reduction was promoted by hydrophobic environments.

DOI： 10.1002/anie.202014323

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Authorship：Lead author   Language：English   Publisher：CHEMICAL SOC JAPAN  

Unique structures and functions of porous ionic crystals (PICs) based on polyoxometalate (POM) anions, which are different from typical porous crystalline materials such as zeolites and metal-organic frameworks (MOFs), can be summarized as follows. (i) Crystal structures of PICs are often flexible since Coulomb interaction works isotropically in a long-range, so that structural transformation occurs to adapt to specific guest molecules. (ii) POMs show reversible redox properties leading to the formation of "redox-active" porous materials. (iii) Ionic building blocks create strong electrostatic fields in the pore, which are suitable for accommodating and stabilizing polar guests and ionic intermediates. (iv) Various cations can be incorporated as counter cations of POMs to fine-tune the functions. The crystal structures and functions of PICs can be controlled by the appropriate choice of molecular cations (macrocations) as ionic building blocks as well as the symmetry, size, and charge of POMs. In particular, oxo-centered trinuclear metal (M-III) carboxylates with a general formula of [M3O(OOCR)(6)(L)(3)](+) as macrocations allow controlling the crystal structures of PICs through the bridging ligands (R) and terminal ligands (L). The fine-tuned structures of PICs lead to unique functions in gas/solvent sorption/separation, heterogeneous catalysis, redox-induced ion-uptake/release, synthesis of mixed-valance metal nanoclusters, and so on.

DOI： 10.1246/cl.200603

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Eleven isostructural mesoporous ionic crystals (meso-PICs) are synthesized. The initial activities of the Barbier-Grignard reaction, which is a typical C-C bond formation reaction, catalyzed by the meso-PICs are dependent on the acid dissociation constant of the aqua ions of Mn+ and the types of polyoxometalates, which construct the meso-PICs.

DOI： 10.1039/d0dt01202e

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Amorphous high-surface-area aluminum hydroxide-bicarbonates were synthesized starting from AlCl3, base, and bicarbonate in water. Composites with a chemical formulas of [Al13O4(mu-OH)(24)(H2O)(6.5)(OH)(5.5)](HCO3)(1.5) (I-NaOH) and [Al13O4(mu- OH)(24)(H2O)(6)(OH)(6)](HCO3) (I-NH3) were obtained by the use of NaOH/NaHCO3 and NH3/NH4HCO3 as base/bicarbonate, respectively. The surface area of the composites was highly dependent on the pH level of the synthetic solution, and composites with high surface areas (ca. 200 m(2) g(-1)) were obtained around pH 7-8. Pore-size distributions determined from the N-2 adsorption isotherms showed that I-NH3 and I-NaOH possess mainly large (pore radius r(p) > 3 nm) and small (r(p) < 3 nm) pores, respectively, despite similar surface areas. While SEM images showed that both I-NH3 and I-NaOH were aggregates of nanoparticles, the particles were more fused in I-NaOH, which is in line with the existence of small pores and the use of a stronger base (NaOH), which would facilitate the dehydration condensation reaction. The composites were applied as adsorbents to remove methyl orange (MO) from water. The time course of MO adsorption was readily fitted with a pseudo-second-order model, and over 90% MO removal was attained within 10 min with I-NH3, while I-NaOH showed much less MO removal (26%). The MO adsorption isotherm of I-NH3 was reproduced with a Langmuir model with an adsorption capacity of 154 mg g(-1). Notably, the aluminum hydroxide-bicarbonates could not absorb methylene blue, which is a cationic dye, while anions (MO and PO43-) were readily absorbed. Solid-state Al-27 MAS NMR spectra showed that the concentration of 5-coordinated aluminum species, which may serve as guest binding sites, was higher for I-NH3. These results show that electrostatic interaction between anionic MO and coordinatively unsaturated 5-coordinated cationic aluminum species and the large external surface area of I-NH3 contribute to the highly efficient MO adsorption.

DOI： 10.1021/acs.langmuir.0c00021

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The mechanism of the Pd/Ag dual-catalyzed cross-dehydrogenative coupling (CDC) between perfluoroarenes and thiophenes was clarified. The exact role of the catalytic resting state of the homo-biaryl-Pd(II) complex, which was previously overlooked in Pd/Ag dual-catalyzed CDC, was carefully investigated. Detailed experimental studies indicated that a homo-biaryl-Pd(II) complex occurred in the catalytic off-cycle as a resting state and prevented the homocoupling of perfluoroarenes. In addition, these studies indicated that the C-H bond activation steps of perfluoroarenes and thiophenes proceeded by different mechanisms. While the C-H bond of perfluoroarenes was immediately activated by Ag(I) salts, the C-H bond of thiophenes was activated by the Pd(II) catalyst. Kinetic studies revealed that the Pd(II)-C-H activation of thiophenes is most likely the rate-determining step.

DOI： 10.1021/acscatal.9b05326

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Polycondensation via Pd-catalyzed cross-dehydrogenative-coupling reaction of 2,2',3,3',5,5',6,6'-octafluorobiphenyl with thiophene analogues was studied. The synthetic protocol, in which employment of prefunctionalized starting monomers was fully avoided, allowed straightforward access to an alternating pi-conjugated polymer. The addition of K2CO3 to the catalytic system promotes the cross-coupling reaction and suppresses the undesired homocoupling reaction, producing the corresponding donor acceptor type pi-conjugated polymers with minor homocoupling defects. The reaction also proceeded using O-2 as the terminal oxidant, resulting in lower loading of the Ag oxidant. The obtained polymer was evaluated as an emitting material for an organic light-emitting diode.

DOI： 10.1021/acsmacrolett.7b00887

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