7 research outputs found

    Soft Propargylic Deprotonation: Designed Ligand Enables Au-Catalyzed Isomerization of Alkynes to 1,3-Dienes

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    By functionalizing the privileged biphenyl-2-ylphosphine with a basic amino group at the rarely explored 3′ position, the derived gold­(I) complex possesses orthogonally positioned “push” and “pull” forces, which enable for the first time soft propargylic deprotonation and permit the bridging of a difference of >26 p<i>K</i><sub>a</sub> units (in DMSO) between a propargylic hydrogen and a protonated tertiary aniline. The application of this design led to efficient isomerization of alkynes into versatile 1,3-dienes with synthetically useful scope under mild reaction conditions

    Ligand-Accelerated Gold-Catalyzed Addition of in Situ Generated Hydrazoic Acid to Alkynes under Neat Conditions

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    The direct addition of in situ generated hydrazoic acid to alkynes is realized without solvent by using a gold catalyst derived from a recently designed remotely functionalized biaryl-2-ylphosphine ligand (i.e., WangPhos). With terminal alkynes, the additions are mostly realized with 0.1 mol% catalyst loadings and at 40 °C. With more challenging internal alkynes devoid of direct EWG substitution, the one-step transformation is realized for the first time with generally high efficiency at ambient temperature

    One-Pot Synthesis of Benzene-Fused Medium-Ring Ketones: Gold Catalysis-Enabled Enolate Umpolung Reactivity

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    Enolate umpolung reactivities offer valuable and potentially unique alternatives over the enolate counterparts for the construction of ubiquitous carbonyl compounds. We disclose here that <i>N</i>-alkenoxypyridinium salts, generated readily upon gold-catalyzed additions of protonated pyridine <i>N</i>-oxide to C–C triple bonds of unactivated terminal alkynes, display versatile enolate umpolung chemistry upon heating and react with tethered arene nucleophiles in an S<sub>N</sub>2′ manner. In a synthetically efficient one-pot, two-step process, this chemistry enables expedient preparation of valuable benzo-fused seven-/eight-membered cyclic ketones, including those of O-/N-heterocycles, from easily accessible aryl-substituted linear alkyne substrates. The reaction yields can be up to 87%

    Remote Cooperative Group Strategy Enables Ligands for Accelerative Asymmetric Gold Catalysis

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    An accelerative asymmetric gold catalysis is achieved for the first time via chiral ligand metal cooperation. An asymmetrically positioned remote amide group in the designed chiral binaphthyl-based ligand plays the essential role of a general base catalyst and selectively accelerates the cyclizations of 4-allen-1-ols into one prochiral allene face. The reactions are mostly highly enantioselective with achiral substrates, and due to the accelerated nature of the catalysis catalyst loadings as low as 100 ppm are allowed. With a pre-existing chiral center at any of the backbone sp<sup>3</sup>-carbons, the reaction remained highly efficient and most importantly maintained excellent allene facial selectivities regardless of the substrate stereochemistry. By using different combinations of ligand and substrate enantiomers, it is now possible to access all four stereoisomers of versatile 2-vinyltetrahydrofurans with exceedingly high selectivity. The underpinning design of this chemistry reveals a novel and conceptually distinctive strategy to tackle challenging asymmetric gold catalysis, which to date has relied on decelerative asymmetric steric hindrance approaches

    Electron-Rich Two-Dimensional Molybdenum Trioxides for Highly Integrated Plasmonic Biosensing

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    Two-dimensional (2D) plasmonic materials facilitate exceptional light–matter interaction and enable in situ plasmon resonance tunability. However, surface plasmons of these materials mainly locate intrinsically at the long wavelength range that are not accessible for practical applications. To address this fundamental challenge, transition metal oxides with atomically layered structure as well as free carriers doping capability have been considered as an alternative class of 2D plasmonic material for achieving tunable plasmonic properties in the visible and near-infrared range. Here, we synthesize few-layer α-MoO<sub>3</sub> nanoflakes that are heavily doped with free electrons via H<sup>+</sup> intercalation. The resultant substoichiometric MoO<sub>3–<i>x</i></sub> nanoflakes provide strong plasmon resonance located at ∼735 nm. Moreover, the MoO<sub>3–<i>x</i></sub> nanoflakes carrying positive charges show stable attachment to polyanions functionalized microfiber and good affinity to negatively charged biomolecules. Our experimental demonstration of fiber-optic biosensing platform provides a detection limit of bovine serum albumin as low as 1 pg/mL, and proves the feasibility and prospects of employing 2D MoO<sub>3–<i>x</i></sub> plasmonic nanoflakes in highly integrated devices compliant with frequently used and cost-effective optical system

    Ordered and Atomically Perfect Fragmentation of Layered Transition Metal Dichalcogenides <i>via</i> Mechanical Instabilities

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    Thermoplastic polymers subjected to a continuous tensile stress experience a state of mechanical instabilities, resulting in neck formation and propagation. The necking process with strong localized strain enables the transformation of initially brittle polymeric materials into robust, flexible, and oriented forms. Here we harness the polymer-based mechanical instabilities to control the fragmentation of atomically thin transition metal dichalcogenides (TMDs). We develop a simple and versatile nanofabrication tool to precisely fragment atom-thin TMDs sandwiched between thermoplastic polymers into ordered and atomically perfect TMD nanoribbons in arbitrary directions regardless of the crystal structures, defect content, and original geometries. This method works for a very broad spectrum of semiconducting TMDs with thicknesses ranging from monolayers to bulk crystals. We also explore the electrical properties of the fabricated monolayer nanoribbon arrays, obtaining an on/off ratio of ∼10<sup>6</sup> for such MoS<sub>2</sub> arrays based field-effect transistors. Furthermore, we demonstrate an improved hydrogen evolution reaction with the resulting monolayer MoS<sub>2</sub> nanoribbons, thanks to the largely increased catalytic edge sites formed by this physical fragmentation method. This capability not only enriches the fundamental study of TMD extreme and fragmentation mechanics, but also impacts on future developments of TMD-based devices
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