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    General Chemistry

    A Facile Route to Nonlinear Optical Materials: Three‐Site Aliovalent Substitution Involving One Cation and Two Anions

    Trading places: Two new nonlinear optical materials, α‐ and β‐Ba2[GaF4(IO3)2](IO3) (1 and 2), were designed via three‐site aliovalent substitution of VO4F2 in α‐ and β‐Ba2[VO2F2(IO3)2](IO3) by GaO2F4. The new materials display large second‐harmonic generation responses (≈6×KH2PO4 (KDP)), wide energy band gaps (4.61 and 4.35 eV), and high laser damage thresholds (29.7× and 28.3× relative to that of AgGaS2).

    Abstract

    Two mixed‐metal gallium iodate fluorides, namely, α‐ and β‐Ba2[GaF4(IO3)2](IO3) (1 and 2), have been designed by the aliovalent substitutions of α‐ and β‐Ba2[VO2F2(IO3)2](IO3) (3 and 4) involving one cationic and two anionic sites. Both 1 and 2 display large second‐harmonic generation responses (≈6×KH2PO4 (KDP)), large energy band gaps (4.61 and 4.35 eV), wide transmittance ranges (≈0.27–12.5 μm), and high relevant laser‐induced damage thresholds (29.7× and 28.3×AgGaS2, respectively), which indicates that 1 and 2 are potential second‐order nonlinear optical materials in the ultraviolet to mid‐infrared. Our studies propose that three‐site aliovalent substitution is a facile route for the discovery of good NLO materials.

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    Source:: Angewandte Chemie Int. edition

          

    Access to N‐Substituted 2‐Pyridones by Catalytic Intermolecular Dearomatization and 1,4‐Acyl Transfer

    When the fearless Don Quixote was charging at windmills, he left his slow companion, Sancho Panza, behind. In their Communication (DOI: 10.1002/anie.201812937), J. Sun et al. describe a novel rhodium‐catalyzed dearomatization and rearrangement of O‐substituted pyridines to access N‐substituted 2‐pyridones, a challenging target since their straightforward synthesis by simple alkylation of 2‐pyridones is thwarted by their preferred O‐reactivity. The key to this transformation is the formation of the pyridinium ylide and subsequent 1,4‐acyl migratory rearrangement.

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    Source:: Angewandte Chemie Int. edition

          

    Helicoidal Patterning of Nanorods with Polymer Ligands

    Gold nanorods, end‐grafted with achiral polymer ligands, show a new mechanism of chiral surface patterning giving a helicoidal morphology. This morphology is dictated by the relationship between the polymer grafting density and the ratio of the polymer length to the nanorod radius.

    Abstract

    Chiral packing of ligands on the surface of nanoparticles (NPs) is of fundamental and practical importance, as it determines how NPs interact with each other and with the molecular world. Herein, for gold nanorods (NRs) capped with end‐grafted nonchiral polymer ligands, we show a new mechanism of chiral surface patterning. Under poor solvency conditions, a smooth polymer layer segregates into helicoidally organized surface‐pinned micelles (patches). The helicoidal morphology is dictated by the polymer grafting density and the ratio of the polymer ligand length to nanorod radius. Outside this specific parameter space, a range of polymer surface structures was observed, including random, shish‐kebab, and hybrid patches, as well as a smooth polymer layer. We characterize polymer surface morphology by theoretical and experimental state diagrams. The helicoidally organized polymer patches on the NR surface can be used as a template for the helicoidal organization of other NPs, masked synthesis on the NR surface, as well as the exploration of new NP self‐assembly modes.

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    Source:: Angewandte Chemie Int. edition

          

    Atomically Dispersed Molybdenum Catalysts for Efficient Ambient Nitrogen Fixation

    Electrocatalytic N2 reduction under ambient conditions offers a promising carbon‐free strategy toward clean and sustainable NH3 production. In their Communication (DOI: 10.1002/anie.201811728), J. Luo, R. R. Adzic, H. L. Xin et al. report single molybdenum atoms anchored on nitrogen‐doped porous carbon. The catalyst achieves a high NH3 yield rate, Faradaic efficiency, and stability at room temperature because of a high density of active sites within a hierarchically porous carbon framework.

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    Source:: Angewandte Chemie Int. edition

          

    Anchoring an Artificial Solid–Electrolyte Interphase Layer on a 3D Current Collector for High‐Performance Lithium Anodes

    3D copper anchored with an artificial solid–electrolyte interface (SEI) layer is proposed for Li‐plating. The anchoring construction of 3D copper and SEI layer can lower current density, provide buffer space, reduce lithium/electrolyte contact, and endure Li‐deposition‐induced volume change, leading to high‐performance lithium anode with long lifespan, high rate, high area capacity, and high efficiency.

    Abstract

    The application of Li anodes is hindered by dendrite growth and side reactions between Li and electrolyte, despite its high capacity and low potential. A simple approach for this challenge is now demonstrated. In our strategy, the garnet‐type Li6.4La3Zr1.4Ta0.6O12 (LLZTO)‐based artificial solid–electrolyte interphase (SEI) is anchored on Cu foam by sintering the Cu foam coated with LLZTO particles. The heat treatment leads to the interdiffusion of Cu and Ta2O5 at the Cu/LLZTO interface, through which LLZTO layer is fixed on Cu foam. 3D structure lowers the current density, and meanwhile the SEI reduces the contact of Li and electrolyte. Furthermore, the anchoring construction can endure Li‐deposition‐induced volume change. Therefore, LLZTO‐modified Cu foam shows much improved Li plating/stripping performance, including long lifespan (2400 h), high rate (maximum current density of 20 mA cm−2), high areal capacity (8 mA h cm−2 for 100 cycles), and high efficiency (over 98 %).

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    Source:: Angewandte Chemie Int. edition

          

    Activating a Peroxo Ligand for C−O Bond Formation

    Taming oxygen for effective cleavage of the O−O bond and a further C−O bond formation has been achieved through proton transfer/electron transfer steps. A free radical mechanism accounts for the transformation of peroxide complexes into water and 2‐iradaoxetane complexes (see scheme; C gray, Ir green, N blue, O red; Mepy=4‐methylpyridine).

    Abstract

    Dioxygen activation for effective C−O bond formation in the coordination sphere of a metal is a long‐standing challenge in chemistry for which the design of catalysts for oxygenations is slowed down by the complicated, and sometimes poorly understood, mechanistic panorama. In this context, olefin–peroxide complexes could be valuable models for the study of such reactions. Herein, we showcase the isolation of rare “Ir(cod)(peroxide)” complexes (cod=1,5‐cyclooctadiene) from reactions with oxygen, and then the activation of the peroxide ligand for O−O bond cleavage and C−O bond formation by transfer of a hydrogen atom through proton transfer/electron transfer reactions to give 2‐iradaoxetane complexes and water. 2,4,6‐Trimethylphenol, 1,4‐hydroquinone, and 1,4‐cyclohexadiene were used as hydrogen atom donors. These reactions can be key steps in the oxy‐functionalization of olefins with oxygen, and they constitute a novel mechanistic pathway for iridium, whose full reaction profile is supported by DFT calculations.

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    Source:: Angewandte Chemie Int. edition

          

    PdII‐Catalyzed Enantioselective C(sp3)−H Activation/Cross‐Coupling Reactions of Free Carboxylic Acids

    Worth protecting: PdII‐catalyzed enantioselective C(sp3)−H cross‐coupling of free carboxylic acids with organoborons has been realized using either mono‐protected amino acid (MPAA) ligands or mono‐protected aminoethyl amine (MPAAM) ligands. A diverse range of aryl‐ and vinyl‐boron reagents can be used as coupling partners to provide chiral carboxylic acids.

    Abstract

    PdII‐catalyzed enantioselective C(sp3)−H cross‐coupling of free carboxylic acids with organoborons has been realized using either mono‐protected amino acid (MPAA) ligands or mono‐protected aminoethyl amine (MPAAM) ligands. A diverse range of aryl‐ and vinyl‐boron reagents can be used as coupling partners to provide chiral carboxylic acids. This reaction provides an alternative approach to the enantioselective synthesis of cyclopropanecarboxylic acids and cyclobutanecarboxylic acids containing α‐chiral tertiary and quaternary stereocenters. The utility of this reaction was further demonstrated by converting the carboxylic acid into cyclopropyl amine without loss of optical activity.

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    Source:: Angewandte Chemie Int. edition

          

    Palladium/Norbornene‐Catalyzed Indenone Synthesis from Simple Aryl Iodides: Concise Syntheses of Pauciflorol F and Acredinone A

    A straightforward method for indenone synthesis was achieved by Pd/NBE‐catalyzed annulation between simple aryl iodides and unsaturated carboxylic acid anhydrides. This method enabled streamlined syntheses of pauciflorol F and acredinone A.

    Abstract

    To show the synthetic utility of palladium/norbornene (Pd/NBE) cooperative catalysis, here we report concise syntheses of indenone‐based natural products, pauciflorol F and acredinone A, which are enabled by direct annulation between aryl iodides and unsaturated carboxylic acid anhydrides. Compared to the previous indenone‐preparation approaches, this method allows simple aryl iodides to be used as substrates with complete control of the regioselectivity. The total synthesis of acredinone A features two different Pd/NBE‐catalyzed ortho acylation reactions for constructing penta‐substituted arene cores, including the development of a new ortho acylation/ipso borylation.

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    Source:: Angewandte Chemie Int. edition

          

    Precise In Vivo Inflammation Imaging Using In Situ Responsive Cross‐linking of Glutathione‐Modified Ultra‐Small NIR‐II Lanthanide Nanoparticles

    Ray of light: An in vivo, reactive oxygen species (ROS)‐responsive, cross‐linking strategy was developed utilizing glutathione‐modified, sub‐10 nm, ultra‐small nanoprobes to improve NIR‐II bioimaging and excretion properties.

    Abstract

    To improve the bioimaging signal‐to‐noise ratio (SNR), long‐term imaging capability, and decrease the potential biotoxicity, an in vivo cross‐linking strategy was developed by using sub‐10 nm, glutathione‐modified, lanthanide nanoprobes. After administration, the nanoprobes cross‐link in response to reactive oxygen species (ROS) at the inflamed area and enable the quick imaging of ROS in the second near‐infrared (NIR‐II) window. These nanoprobes could be rapidly excreted due to their ultra‐small size. This strategy may also be applied to other ultra‐small contrast agents for the precise bioimaging by in situ lesion cross‐linking.

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    Source:: Angewandte Chemie Int. edition

          

    Activating Inert Metallic Compounds for High‐Rate Lithium–Sulfur Batteries Through In Situ Etching of Extrinsic Metal

    Vacant defects bring activity to multimetallic alloys for cathode redox reactions in lithium–sulfur batteries. In their Communication (DOI: 10.1002/anie.201812062), J.‐Q. Huang et al. show that the introduction and in situ etching of an extrinsic metal to a monometallic compound activates the originally inert phase for kinetic propelling of polysulfide‐involving surface reactions at a high rate. Remarkable cycling stability is found at a high sulfur loading of 4.8 mg cm−2.

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    Source:: Angewandte Chemie Int. edition

          

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