Phase Behavior of a Hydrogen-Bonded Polymer with Lamella-to-Cylinder Transition: Complex of Poly(4-vinylpyridine) and Small Dendritic Benzoic Acid Derivative

Phase behavior of a supramolecular system based on poly­(4-vinylpyridine) (P4VP) and 3,4,5-tris­(dodecyloxy)­benzoic acid (TDBA) [P4VP­(TDBA)_<i>x</i>, where <i>x</i> is the molar ratio of TDBA to P4VP repeating unit] was investigated by means of FTIR, differential scanning calorimetry, polarized optical microscopy, and X-ray scattering method. The intermolecular hydrogen-bonding interaction between P4VP and TDBA is confirmed by FTIR. While almost all of the added TDBA molecules are hydrogen bonded to the P4VP chains at <i>x</i> < ∼0.60, the hydrogen-bonding interaction becomes incomplete at <i>x</i> > 0.60 and saturates at <i>x</i> > 0.90. The phase structure of P4VP­(TDBA)_<i>x</i> is composition dependent. At <i>x</i> < ∼0.30, the complex is homogeneous. With ∼0.30 < <i>x</i> < ∼0.60, P4VP­(TDBA)_<i>x</i> forms a lamella phase, of which the long period is proportional to 1/<i>x</i>. Further adding TDBA causes a lamella-to-cylinder transition. At <i>x</i> > ∼0.60, the lattice parameter of the cylinder or hexagonal columnar (Φ_H) phase decreases with increasing <i>x</i>. Considering the microphase separation between the polar part and the nonpolar part of alkyl tails, the lamella-to-cylinder transition can be understood using a volumetric argument. We consider that the large nonpolar part of TDBA enhances the microphase separation of P4VP­(TDBA)_<i>x</i>, and moreover, the fan-like shape of TDBA facilitates the formation of Φ_H phase. We also roughly estimated the domain size of the P4VP chains in the microphase-separated mesophase. For both the lamellar and Φ_H phase, increasing <i>x</i> results in stronger confinement on the P4VP chains. During the lamella-to-cylinder transition the confinement imposed by the TDBA molecules may be partially released, which favors the Φ_H phase formation

A Highly Regio- and Stereoselective Synthesis of α‑Fluorinated Imides via Fluorination of Chiral Enamides

A highly π-facial selective and regioselective fluorination of chiral enamides is described. The reaction involves an enantioselective fluorination exclusively at the electron-rich enamide olefin with N–F reagents such as Selectfluor and <i>N</i>-fluoro-benzene­sulfonimide [NFSI] accompanied by trapping of the β-fluoro-iminium cationic intermediate with water. The resulting <i>N,O</i>-hemiacetal could be oxidized using Dess-Martin periodinane, leading to an asymmetric sequence for syntheses of chiral α-fluoro-imides and optically enriched α-fluoro-ketones

A Highly Regio- and Stereoselective Synthesis of α‑Fluorinated Imides via Fluorination of Chiral Enamides

A highly π-facial selective and regioselective fluorination of chiral enamides is described. The reaction involves an enantioselective fluorination exclusively at the electron-rich enamide olefin with N–F reagents such as Selectfluor and <i>N</i>-fluoro-benzene­sulfonimide [NFSI] accompanied by trapping of the β-fluoro-iminium cationic intermediate with water. The resulting <i>N,O</i>-hemiacetal could be oxidized using Dess-Martin periodinane, leading to an asymmetric sequence for syntheses of chiral α-fluoro-imides and optically enriched α-fluoro-ketones

A Highly Regio- and Stereoselective Synthesis of α‑Fluorinated Imides via Fluorination of Chiral Enamides

A highly π-facial selective and regioselective fluorination of chiral enamides is described. The reaction involves an enantioselective fluorination exclusively at the electron-rich enamide olefin with N–F reagents such as Selectfluor and <i>N</i>-fluoro-benzene­sulfonimide [NFSI] accompanied by trapping of the β-fluoro-iminium cationic intermediate with water. The resulting <i>N,O</i>-hemiacetal could be oxidized using Dess-Martin periodinane, leading to an asymmetric sequence for syntheses of chiral α-fluoro-imides and optically enriched α-fluoro-ketones

Robust Phase Control through Hetero-Seeded Epitaxial Growth for Face-Centered Cubic Pt@Ru Nanotetrahedrons with Superior Hydrogen Electro-Oxidation Activity

Controllable synthesis of metallic nanocrystals (NCs) with tunable phase, uniform shape, and size is of multidisciplinary interests but has still remained challenging. Herein, a robust phase control strategy is developed, in which seeds with a given phase are added to guide the epitaxial growth of the target metal to inherit the seeds’ phase. Through this strategy, M@Ru (M = Pt, Pd) NCs in the face-centered cubic (<i>fcc</i>) phase, a metastable phase for Ru under ambient conditions, were synthesized with the hydrothermal method. The Pt@Ru NCs showed not only the pure <i>fcc</i> phase but also high morphology selectivity to tetrahedrons surrounded by {111} facets. As revealed by density function theory (DFT) calculations, the preferentially epitaxial growth of Ru atom layers on the nonclosest-packed facets of hetero <i>fcc</i> metal seeds led to the formation of <i>fcc</i> Ru shells. Furthermore, the <i>fcc</i> Pt@Ru tetrahedrons/C showed electrocatalytic activity enhancement with more than an order of magnitude toward hydrogen oxidation reaction (HOR) in acidic electrolyte compared with hydrothermally synthesized Ru/C. Electrochemical measurement combined with DFT calculations revealed that the optimum HOR activity should be achieved on well-crystallized <i>fcc</i> Ru catalysts exposing maximum {111} facets

Robust Phase Control through Hetero-Seeded Epitaxial Growth for Face-Centered Cubic Pt@Ru Nanotetrahedrons with Superior Hydrogen Electro-Oxidation Activity

Controllable synthesis of metallic nanocrystals (NCs) with tunable phase, uniform shape, and size is of multidisciplinary interests but has still remained challenging. Herein, a robust phase control strategy is developed, in which seeds with a given phase are added to guide the epitaxial growth of the target metal to inherit the seeds’ phase. Through this strategy, M@Ru (M = Pt, Pd) NCs in the face-centered cubic (<i>fcc</i>) phase, a metastable phase for Ru under ambient conditions, were synthesized with the hydrothermal method. The Pt@Ru NCs showed not only the pure <i>fcc</i> phase but also high morphology selectivity to tetrahedrons surrounded by {111} facets. As revealed by density function theory (DFT) calculations, the preferentially epitaxial growth of Ru atom layers on the nonclosest-packed facets of hetero <i>fcc</i> metal seeds led to the formation of <i>fcc</i> Ru shells. Furthermore, the <i>fcc</i> Pt@Ru tetrahedrons/C showed electrocatalytic activity enhancement with more than an order of magnitude toward hydrogen oxidation reaction (HOR) in acidic electrolyte compared with hydrothermally synthesized Ru/C. Electrochemical measurement combined with DFT calculations revealed that the optimum HOR activity should be achieved on well-crystallized <i>fcc</i> Ru catalysts exposing maximum {111} facets