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