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Transition metal-catalyzed decarboxylative cross-coupling reactions have recently emerged as a new and important category of organic transformations that find versatile applications in the construction of carbon-carbon and carbon-heteroatom bonds. The use of relatively cheap and stable carboxylic acids to replace organometallic reagents enables the decarboxylative cross-coupling reactions to proceed with good selectivities and functional group tolerance. In the present review we summarize the various types of decarboxylative cross-coupling reactions catalyzed by different transition metal complexes. The scope and applications of these reactions are described. The challenges and opportunities in the field are discussed.

We have calculated the longitudinal acoustic phonon limited electron mobility of 14 twvo-dimensional semiconductors with composition of MX2, where M （= Mo, W, Sn, Hf, Zr and Pt） is the transition metal, and X is S, Se and Te. We treated the scattering matrix by the deformation potential approximation. We found that out of 14 compounds, MoTe2, HfSe2 and ZrSe2 are promising regarding to their possible high mobility and finite band gap. The phonon limited mobility can be above 2,500 cm^2·V^-1·s^-1 at room temperature.

Highly active and low-cost catalysts for electrochemical reactions such as the hydrogen evolution reaction （HER） are crucial for the development of efficient energy conversion and storage technologies. Theoretical simulations have been instrumental in revealing the correlations between the electronic structure of materials and their catalytic activity, and guide the prediction and development of improved catalysts. However, difficulties in accurately engineering the desired atomic sites lead to challenges in making direct comparisons between experi- mental and theoretical results. In MoS2, the Mo-edge has been demonstrated to be active for HER whereas the S-edge is inert. Using a computational descriptor- based approach, we predict that by incorporating transition metal atoms （Fe, Co, Ni, or Cu） the S-edge site should also become HER active. Vertically standing, edge-terminated MoS2 nanofilms provide a well-defined model system for verifying these predictions. The transition metal doped MoS2 nanofilms show an increase in exchange current densities by at least two-fold, in agreement with the theoretical calculations. This work opens up further opportunities for improving electrochemical catalysts by incorporating promoters into particular atomic sites, and for using well-defined systems in order to understand the origin of the promotion effects.

In the past thirty years, transition metal catalyzed silylation of inert C-H bonds has attracted intensive attention due to the im- portance and wide use of organosilicon compounds. In this review, the silylation reactions of inert C-H bonds catalyzed by transition metal complexes of Ir, Rh, Ru, Pt, Pd, Ni, and Sc, and the strategies utilized to access the site-selective C-H silyla- tion products have been summarized. Furthermore, the mechanisms of C-H silylation reactions have been discussed briefly.

The electrical performance of two-dimensional transition metal dichalcogenides （TMDs） is strongly affected by the number of structural defects. In this work, we provide an optical spectroscopic characterization approach to correlate the number of structural defects and the electrical performance of WSe2 devices. Low-temperature photoluminescence （PL） spectra of electron-beam-lithography- processed WSe2 exhibit a clear defect-induced PL emission due to excitons bound to defects, which would strongly degrade the electrical performance. By adopting an electron-beam-free transfer-electrode technique, we successfully prepared a backgated WSe2 device containing a limited amount of defects. A maximum hole mobility of approximately 200 cm2.V -1.s-1 was achieved because of the reduced scattering sources, which is the highest reported value for this type of device. This work provides not only a versatile and nondestructive method to monitor the defects in TMDs but also a new route to approach the room-temperature phonon-limited mobility in high-performance TMD devices.

In the past few years, two-dimensional （2D） transition metal dichalcogenide （TMDC） materials have attracted increasing attention of the research community, owing to their unique electronic and optical properties, ranging from the valley-spin coupling to the indirect-to-direct bandgap transition when scaling the materials from multi-layer to monolayer. These properties are appealing for the development of novel electronic and optoelectronic devices with important applications in the broad fields of communication, computation, and healthcare. One of the key features of the TMDC family is the indirect-to-direct bandgap transition that occurs when the material thickness decreases from multilayer to monolayer, which is favorable for many photonic applications. TMDCs have also demonstrated unprecedented flexibility and versatility for constructing a wide range of heterostructures with atomic-level control over their layer thickness that is also free of lattice mismatch issues. As a result, layered TMDCs in combination with other 2D materials have the potential for realizing novel high-performance optoelectronic devices over a broad operating spectral range. In this article, we review the recent progress in the synthesis of 2D TMDCs and optoelectronic devices research. We also discuss the challenges facing the scalable applications of the family of 2D materials and provide our perspective on the opportunities offered by these materials for future generations of nanophotonics technology.

We review lattice vibrational modes in atomically thin two-dimensional （2D） layered materials, focusing on 2D materials beyond graphene, such as group VI transition metal dichalcogenides, topological insulator bismuth chalcogenides, and black phosphorus. Although the composition and structure of those materials are remarkably different, they share a common and important feature, i.e., their bulk crystals are stacked via van der Waals interactions between ＂layers＂, while each layer is comprised of one or more atomic planes. First, we review the background of some 2D materials （MX2, M = Mo, W; X = S, Se, Te. Bi2X3, X = Se, Te. Black phosphorus）, including crystalline structures and stacking order. We then review the studies on vibrational modes of layered materials and nanostructures probed by the powerful yet nondestructive Raman spectroscopy technique. Based on studies conducted before 2010, recent investigations using more advanced techniques have pushed the studies of phonon modes in 2D layered materials to the atomically thin regime, down to monolayers. We will classify the recently reported general features into the following categories： phonon confinement effects and electron-phonon coupling, anomalous shifts in high-frequency intralayer vibrational modes and surface effects, reduced dimensionality and lower symmetry, the linear chain model and the substrate effect, stacking orders and interlayer shear modes, polarization dependence, and the resonance effect. Within the seven categories, both intralayer and interlayer vibrational modes will be discussed. The comparison between different materials will be provided as well.

Transition-metal-catalyzed C-H bond activation represents one of the most attractive research areas in organic synthesis. In contrast to the great developments made in directed C-H bond functionalization of arenes, the directing group-assisted activa- tion of non-aromatic vinylic C-H bonds still remains challenging. During the recent years, significant progress has been made in this fascinating field with various functionalized alkenes, heterocycles and carbocycles being obtained. This article will fo- cus on the recent achievements in the field of directing-group-assisted vinylic C-H bond functionalization.

Transition-metal dichalcogenides （TMDs） exhibit immense potential as lithium/ sodium-ion electrode materials owing to their sandwich-like layered structures. To optimize their lithium/sodium-storage performance, two issues should be addressed： fundamentally understanding the chemical reaction occurring in TMD electrodes and developing novel TMDs. In this study, WSe2 hexagonal nanoplates were synthesized as lithium/sodium-ion battery （LIB/SIB） electrode materials. For LIBs, the WSe2-nanoplate electrodes achieved a stable reversible capacity and a high rate capability, as well as an ultralong cycle life of up to 1,500 cycles at 1,000 mA·g^-1. Most importantly, in situ Raman spectroscopy, ex situ X-ray diffraction （XRD）, transmission electron microscopy, and electrochemical impedance spectroscopy measurements performed during the discharge-charge process clearly verified the reversible conversion mechanism, which can be summarized as follows： WSe2 ＋ 4Li^＋ ＋ 4e^- ←→ W ＋ 2Li2Se. The WSe2 nanoplates also exhibited excellent cycling performance and a high rate capability as SIB electrodes. Ex situ XRD and Raman spectroscopy results demonstrate that WSe2 reacted with Na^＋ more easily and thoroughly than with Li^＋ and converted to Na2Se and tungsten in the Ist sodiated state. The subsequent charging reaction can be expressed as Na2Se → Se ＋ 2Na^＋＋ 2e^-, which differs from the traditional conversion mechanism for LIBs. To our knowledge, this is the first systematic exploration of the lithium/sodium-storage performance of WSe2 and the mechanism involved.

The rational design of earth-abundant catalysts with excellent water splitting activities is important to obtain clean fuels for sustainable energy devices. In this study, mixed transition metal oxide nanoparticles encapsulated in nitrogendoped carbon （denoted as AB2O4@NC） were developed using a one-pot protocol, wherein a metal-organic complex was adopted as the precursor. As a proof of concept, MnCo2O4@NC was used as an electrocatalyst for water oxidation, and demonstrated an outstanding electrocatalytic activity with low overpotential to achieve a current density of 10 mA·cm^-1 0/10 = 287 mV）, small Tafel slope （55 mV·dec^-1）, and high stability （96% retention after 20 h）. The excellent electrochemical performance benefited from the synergistic effects of the MnCo2O4 nanoparticles and nitrogen-doped carbon, as well as the assembled mesoporous nanowire structure. Finally, a highly stable all-solid-state supercapacitor based on MnCo2O4@NC was demonstrated （1.5% decay after 10,000 cycles）.