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Geometric optimization and electronic properties of Stone–Wales defective antimonene nanotubes were calculated using the method of first-principles calculations based on density functional theory. The possible orientations of zigzag/armchair nanostructures when Stone–Wales defects were formed were investigated, respectively. The band structures, partial density of states, and electron density isosurfaces were calculated to reveal the influence of Stone–Wales defects on antimonene nanotubes. When the structure of antimonene changed from monolayer to tube, the indirect gap semiconductor antimonene transformed to a direct gap semiconductor. Moreover, the character of the direct bandgap for the antimonene nanotube was preserved, while the energy of the conduction band bottom changed due to the intervention of the defect energy level in the bandgaps. These findings may provide valuable references for the development and design of novel nanodevices based on antimonene nanotubes.

Purpose High temperature gradient induces high residual stress, producing an important effect on the part manufacturing during laser powder bed fusion (LPBF). The purpose of this study is to investigate the effect of the molten pool mode on the thermal stress of Ti-6Al-4V alloy during different deposition processes. Design/methodology/approach A coupled thermal-mechanical finite element model was built. The developed model was validated by comparing the numerical results with the experimental data in the maximum molten pool temperature, the molten pool dimension and the residual stress described in the previous work. Findings For the single-track process, the keyhole mode caused an increase in both the maximum stress and the high-stress area compared with the conduction mode. For the multitrack process, a lower tensile stress around the scanning track and a higher compressive stress below the scanning track were found in the keyhole mode. For the multilayer process, the stress along the scanning direction at the middle of the part changed from tensile stress to compressive stress with the increase in the deposition layer number. As the powder layer number increased, the stress along the scanning direction near the top surface of the part decreased while the stress along the deposition direction obviously increased, indicating that the stress along the deposition direction became the dominant stress. The keyhole mode can reduce the residual stress near the top of the part, and the conduction mode was more likely to produce a low residual stress near the bottom of the part. Originality/value The results provide a systematic understanding of thermal stress during the LPBF process.

Two-dimensional ferroelastic materials and two-dimensional materials with negative Poisson's ratios have attracted great interest. Here, using first-principles calculations, we reveal monolayer YbX (X = S, Se, Te) materials that harbor both ferroelasticity and negative Poisson's ratios. Indirect wide band gaps of about 3 eV have been found in these three materials. Mechanical analysis reveals that the three materials are flexible and they possess large in-plane negative Poisson's ratios from -0.114 to -0.366. Meanwhile, the ferroelasticity in the monolayer YbX shows moderate energy barriers and strong ferroelastic signals, beneficial for applications in shape memory devices. These intriguing properties make monolayer YbX promising candidate materials for applications in nanoelectronics and nanomechanics.

Porosity is one of the main defects in Al alloy fabricated by laser powder bed fusion (L-PBF). This paper investigated the relationships between the characteristics of porosity, melt pool and process parameters in L-PBF Al Zn alloy. It is found that except the laser power and scan speed, the defocusing amount also has a great influence on the melt pool mode. Under the same laser power and scan speed, changing the defocusing amount results in multiple melt pool modes. In this study, keyhole mode melt pool exists only in small defocusing amount of -2 mm and +2 mm. Conduction mode melt pool exists in all defocusing amount. It is also found that the mode of melt pool and the porosity characteristics are closely related and both are significantly influenced by the process parameters. The melt pool depth increases as laser power increases or scan speed decreases during the process of L-PBF Al Zn alloy. Ratio of melt pool depth to width linearly increases with the growing of the laser energy density. Gas porosity and keyhole porosity exist in keyhole mode melt pool. Lack-of-fusion porosity exists in conduction mode melt pool. Relative densities were measured in this research at different process parameters. The highest relative density can be reached to 99.89%. This study is beneficial for the control of the porosity in L-PBF Al Zn alloy.

Purpose The purpose of this study is to investigate the effect of the strut size and tilt angle on the densification behavior, surface roughness and dimensional accuracy of the selective laser melting AlSi10Mg lattice structure was investigated in this study. In this study, the characteristics such as the density, up-skin and down-skin roughness and dimensional accuracy of selective laser melting forming technology manufacturing (SLMed) AlSi10Mg cellular lattice structure were carried. This work reveals the effect of the strut size and tilt angle on the geometric characteristics of SLMed AlSi10Mg and is benefit for controlling the forming performance of the SLMed cellular lattice structure. Design/methodology/approach Based on AlSi10Mg powder, the influence of the tilt angle changed from 10° to 45° with an increment of 5° were investigated, the influence of the strut size was varied from 0.4 mm to 1.2 mm with an increment of 0.2 mm were investigated. The characteristics such as the density, up-skin and down-skin roughness, dimensional accuracy and mechanical properties of SLM-ed AlSi10Mg cellular lattice structure was carried. Findings Greater than 99% relative density can be achieved for different strut size when optimal process parameters are used. In the optimized process interval, the struts with a tilt angle of 10° can still be formed well, which is higher than the design limit of the inclined angle given in the related literature. The tilt angle has a significant effect on the surface roughness of the strut. The microhardness reached to 157 ± 3 HV, and the maximum compressive strength was 58.86 MPa, with the optimal process parameters. Originality/value In this study, the characteristics such as the density, up-skin and down-skin roughness and dimensional accuracy of SLMed AlSi10Mg cellular lattice structure were carried. With the optimal geometric parameters, the authors tested microhardness and compressive strength of the cellular lattice structure. The results of this study provide theoretical and experimental basis for the realization of high-quality manufacturing and optimization design of aluminum alloy cellular lattice structure, which will meet more diversified industrial needs.

Amides are important structural motifs in pharmaceutical and agrochemical chemistry because of the intriguing biological active properties. We report here the amidation of commercially available es...

Laser powder bed fusion (LPBF) can be directly used to fabricate the metal components with complex structures and high performances. However, the extremely high temperature gradient induces the high residual stress, which leads to deformation or even cracking during the process. A layer-by-layer model was developed to investigate the residual stress of the typical part fabricated by LPBF. The maximum stress was found at the position where the part corner joined with the substrate. The second-largest stress occurred at the top center for the solid parts while occurred at the top center of the long side for the hollow and semi-hollow parts. The residual stress levels of the hollow and semi-hollow parts were obviously less than that of the solid parts, and the residual stress at the middle of the inclined-wall part is lower than that of the thin-walled part. Using the rounded corner instead of the sharp corner and using the arc structure instead of the straight-line structure were helpful in reducing the residual stress in LPBF. The simulated results were in good agreement with the experimental data obtained by the hole-drilling method. The investigated results of this paper can be used to reduce the residual stress in LPBF.

In order to study the mining pressure on the upper coal seam in the fault, the working pressure of the working face with a hard rock roof is based on the production geological conditions of the 3301 working face of Yiqiao Coal Mine. Use flac numerical simulation software to establish a three-dimensional numerical calculation model of mining face, and study the distribution characteristics of mining plastic area, the advance support pressure and elastic strain energy density. And the change curve is treated by origin software fitting function. In the end, it was found that the total volume of the plastic zone and the propulsive distance of the working face showed an exponential function. Before and after the "first square", the total volume of the plastic zone increased more significantly, and the hard roof failure was mainly bending failures; There is a logarithmic function between the advance support pressure and the advancing distance of the working face. The range of 5–14 m in front of the coal wall is a region where the pressure increases sharply. The elastic strain energy density appears relatively high. During the mining process, the advance support of the roadway should be strengthened, and the key monitoring should be carried out. If necessary, corresponding pressure relief measures should be taken to ensure the safe production of the working face.

The large thermal stress caused by the high temperature gradient leads to part deformations which are the important factor restricting the rapid development and wide application of the laser powder bed fusion (LPBF) technology. In the present study, a layer-by-layer model based on the finite element method was developed to study the thin-walled part deformation and the effect caused by the part dimension during LPBF of Ti–6Al–4V alloy. The deformation along the length direction dominated for the thin-walled parts, and the maximum deformation occurred at the middle of the thin-walled part. A mechanism built in the present study revealed the deformation evolution of the thin-walled part. With the increase of the part height and length, the maximum deformation increased first and then tended to be stable. However, the maximum deformation decreased with an increase of the part thickness. Furthermore, a method of compensation design was used to effectively reduce the deformation of the thin-walled part. The simulated results and the deformation control method were validated by the experimental data. The investigated results of this research provide a significant understanding of the part deformation during the LPBF process.

Purpose High residual stress caused by the high temperature gradient brings undesired effects such as shrinkage and cracking in selective laser melting (SLM). The purpose of this study is to predict the residual stress distribution and the effect of process parameters on the residual stress of selective laser melted (SLMed) Inconel 718 thin-walled part. Design/methodology/approach A three-dimensional (3D) indirect sequentially coupled thermal–mechanical finite element model was developed to predict the residual stress distribution of SLMed Inconel 718 thin-walled part. The material properties dependent on temperature were taken into account in both thermal and mechanical analyses, and the thermal elastic–plastic behavior of the material was also considered. Findings The residual stress changes from compressive stress to tensile stress along the deposition direction, and the residual stress increases with the deposition height. The maximum stress occurs at both ends of the interface between the part and substrate, while the second largest stress occurs near the top center of the part. The residual stress increases with the laser power, with the maximum equivalent stress increasing by 21.79 per cent as the laser power increases from 250 to 450 W. The residual stress decreases with an increase in scan speed with a reduction in the maximum equivalent stress of 13.67 per cent, as the scan speed increases from 500 to 1,000 mm/s. The residual stress decreases with an increase in layer thickness, and the maximum equivalent stress reduces by 33.12 per cent as the layer thickness increases from 20 to 60µm. Originality/value The residual stress distribution and effect of process parameters on the residual stress of SLMed Inconel 718 thin-walled part are investigated in detail. This study provides a better understanding of the residual stress in SLM and constructive guidance for process parameters optimization.

In this study, we have performed non-equilibrium molecular dynamics simulation (NEMD) to the interface thermal transport in silicene/stanene hetero-structures, which include the effect of structure size, temperature and defects on the thermal conductance G. The results show that G increases with the temperature significantly, while almost keep constant with the variable of the size of structure. The vacancy defects will lead to the decrease of saturated thermal conductance compared with the defect-free one, which is ascribed to the enhancement of phonon inversion process and the scattering concentration of the phonons. In particular, a singularity point of thermal conductance is found when a single vacancy defect is set in the interface of stanene with the vacancy defect moving. Our result indicates that the thermal conductance of silicene/stanene hetero-structures present remarkable properties (low size dependence and singularities exist as defects move) and are promising for applications of the low dimensional silicene/stanene nanostructure based thermal and nanoelectronic devices.

Here, we report a chromium-catalyzed activation of acyl C-O bonds with magnesium for amidation of esters with nitroarenes. Low-cost chromium(III) chloride shows high reactivity in promoting amidation by using magnesium as reductant and chlorotrimethylsilane as additive. It provides a step-economic strategy to the synthesis of centrally important amide motifs using inexpensive and air-stable nitroarenes as amino sources.

Ensuring the stability of surrounding rock while conducting pressure relief is key to roadway stability control and preventing rock burst. In this paper, segmented enlarged-diameter borehole destressing technology is proposed. The stress distribution around the borehole is analysed based on the theory of elasto-plastic mechanics, and the mechanism of pressure relief for segmented enlarged-diameter boreholes is studied. Secondly, The effects of the diameter of enlarged-diameter section, length of the enlarged-diameter section, and borehole space on pressure relief and roadway deformation were investigated. Finally, the optimal drilling parameters for Tangkou coal mine 6307 working face are analysed. The key parameters of segmented enlarged-diameter borehole pressure relief technology for the 6307 working face were determined and applied in field practice. Field monitoring results showed that the accumulated energy can be effectively reduced using segmented enlarged-diameter pressure relief boreholes, effectively controlling roadway deformation and providing reference for rock burst prevention and roadway stability control.

The discovery of NHCs (NHC = N-heterocyclic carbenes) as ancillary ligands in transition-metal-catalysis ranks as one of the most important developments in synthesis and catalysis. It is now well-recognized that the strong σ-donating properties of NHCs along with the ease of scaffold modification and a steric shielding of the N-wingtip substituents around the metal center enable dramatic improvements in catalytic processes, including the discovery of reactions that are not possible using other ancillary ligands. In this context, although the classical NHCs based on imidazolylidene and imidazolinylidene ring systems are now well-established, recently tremendous progress has been made in the development and catalytic applications of BIAN-NHC (BIAN = bis(imino)acenaphthene) class of ligands. The enhanced reactivity of BIAN-NHCs is a direct result of the combination of electronic and steric properties that collectively allow for a major expansion of the scope of catalytic processes that can be accomplished using NHCs. BIAN-NHC ligands take advantage of (1) the stronger σ-donation, (2) lower lying LUMO orbitals, (3) the presence of an extended π-system, (4) the rigid backbone that pushes the N-wingtip substituents closer to the metal center by buttressing effect, thus resulting in a significantly improved control of the catalytic center and enhanced air-stability of BIAN-NHC-metal complexes at low oxidation state. Acenaphthoquinone as a precursor enables facile scaffold modification, including for the first time the high yielding synthesis of unsymmetrical NHCs with unique catalytic properties. Overall, this results in a highly attractive, easily accessible class of ligands that bring major advances and emerge as a leading practical alternative to classical NHCs in various aspects of catalysis, cross-coupling and C-H activation endeavors.

Selective laser melting (SLM) produces a large amount of residual stress which limits its applicability. Despite the increasing number of studies to understand the relationship between the process parameters and the residual stress, the underlying complex mechanisms are yet to be understood. In this work, a 3D finite element model (FEM) is established to investigate the relationship between the process parameters and the residual stress during SLM. When the process parameters are in different ranges, the residual stress behavior is different. The complex relationship between the residual stress and the process parameters could be the reason for the contradictory parametric effects reported in the literature. The magnitude of the parametric effect on the residual stress is obtained. The influence of the scanning speed is stronger than that of the laser power, which is in turn stronger than that of the hatch spacing. These results can bring insights into the understanding of the residual stress during SLM.

Directional solidification causes a columnar grain microstructure with orientation deviating from building direction to the laser scanning direction which leads to anisotropic mechanical properties of deposited parts in selective laser melting (SLM) additive manufacturing (AM). However, compared to directed energy deposition (DED), the tilt angles between the grain growth orientation and the building direction in SLM are relatively small and hard to investigate due to the high scanning velocity and small facula during processing. This paper investigates the grain growth orientation in the SLM process via finite element analysis and experiments. The maximum heat flow directions and temperature gradients at different deposition heights are studied in order to discuss the local grain growth orientation. Further investigations into the differences in the grain growth orientation under different process parameters have also been carried out. In addition, the research provides a deeper understanding of the grain structures and is expected to help control the solidification texture, which is of vital importance to properties of components.

The synthesis of aromatic ketones by chromium-catalyzed Kumada arylation of secondary amides with organomagnesium reagents is described. This reaction was enabled by using low-cost chromium(III) salt as a precatalyst, combined with trimethylsilyl chloride as an additive, and presents a rare example of catalytic transformation of secondary amides to ketones at room temperature. It was shown that catalytically active low-valent chromium species might be responsible for the amide–ketone exchange by mechanism involving the activation of benzimidate intermediate.

The electronic properties and optical properties of single and double Au-doped phosphorene have been comparatively investigated using the first-principles plane-wave pseudopotential method based on density functional theory. The decrease from direct band gap 0.78 eV to indirect band gap 0.22 and 0.11 eV are observed in the single and double Au-doped phosphorene, respectively. The red shifts of absorbing edge occur in both doped systems, which consequently enhance the absorbing of infrared light in phosphorene. Band gap engineering can, therefore, be used to directly tune the optical absorption of phosphorene system by substitutional Au doping.

A 3D thermo-mechanical finite element model was developed to study the effect of the laser jump speed on the temperature distribution and thermal stress in laser powder bed fusion (LPBF) of Ti6Al4V alloy. Gradient grid and gradient time step were used to further improve solution efficiency. It was found that the temperature of the scanned region rapidly increased as the laser jump speed increased from 100 mm/s to 1000 mm/s. The temperature distribution reached a stable state when the laser jump speed was above 5000 mm/s. The pre-heat peak, the heat peak and the post-heat peak increased with the laser jump speed. The effect of the laser jump speed on the post-heat peak was greater than the pre-heat peak. Compared with the long scan track, the thermal stress distribution varies more sharply with the laser jump speed when using the short scan track. The influence of the laser jump speed on the stress perpendicular to the scan direction was greater than that along the scan direction, whether in a short scan track or in a long scan track. To reduce the residual stress, the length of the scan track should be reduced while the laser jump speed should be increased as much as possible to make the post-heat peak close to the fusion temperature of the material. The simulated results were well validated by the experimental data. The findings of this research help to reduce the thermal stress in laser powder bed fusion.

It was reported a ruthenium-catalyzed ortho-alkynylation of benzoic acids. The reaction was directed by a weakly-coordination carboxyl group, provides a feacile route to the synthesis of ortho-alkynylated derivatives. A rarely example of bis(alkynylation) reaction of C-H bonds was described.

It is reported a weakly coordination-assisted alkynylation of aryl and heteroaryl carboxylic acids with iridium catalysis. The reaction is catalyzed by [{Cp*IrCl2}2] complex without cyclization, forming ortho-alkynylated aryl and heteroaryl carboxylic acids, and features high functional group tolerance and broad substrate scope under an air atmosphere. 2-(Hetero)aryl-substituted acetic acids were amenable to the alkynylation by forming an unusual six-membered ring cycloiridiated intermediate.

The effect of the powder absorptivity on the molten pool dimensions and thermal behavior of SLMed AlSi10Mg has been investigated using finite element analysis in this paper. A transient three-dimensional finite element model using a moving body heat Gaussian energy source is proposed and two absorptivities with large difference were utilized. The results show that higher value of powder absorptivity will obtain larger molten pool dimensions, higher temperature and lower temperature change rate of the first 4 tracks.

In this work, near full density and crack-free hybrid aluminum matrix composites (HAMCs) reinforced with Cr3C2 ceramic particles and Ni–Cr trace elements were successfully fabricated by selective laser melting (SLM). The phase structure, microstructure, mechanical properties and strengthening mechanism of HAMCs were investigated. The results show that various intermetallic compounds, such as Al13Cr2, Al11Cr2 and Al3Ni etc. are generated in HAMCs for the incorporation of trace elements Ni and Cr. These hard-intermetallic compounds provide significant precipitation strengthening effect. Moreover, additions of Cr exert a solid solution strengthening effect because of its good solubility in Al. For the Cr3C2 ceramic, the load transfer from matrix to the reinforcing particles plays an important role on strengthening metal matrix composites. And acicular Al4C3 is formed at the interface between Cr3C2 and the matrix, which improves the interface bonding strength. With various positive strengthening mechanisms, the microhardness of HAMCs increases by 32% and the compressive strength increase by 22%. HAMCs exhibit excellent compressive strength. However, a significant reduction (26%) in tensile properties was found because the crack in the ceramic particle is more sensitive to tensile stress than compressive stress. Micro-particles Cr3C2 are the source of fracture failure of the tensile sample.

By means of comprehensive first-principles calculations, we studied the geometric structure, the stability and electronic properties of the new two-dimensional (2D) Janus MoXB2(X=S, Se) monolayers. Our calculations demonstrated that the predicted Janus MoXB2monolayers are all stable semiconductors with direct band gap. In this paper, we focus on impacts upon the electronic and optical properties of the MoXB2monolayers under the different biaxial strains. With the compressive stress increases, the MoXB2monolayers would become indirect band gap semiconductors, and then behave as semimetal. While under tensile strain, MoXB2still maintain direct band gap. In addition, the optical calculation shows that biaxial strain leads to blue shifts in the optical absorption and reflectivity. The result indicates that MoXB2may be promised nano candidate materials in optoelectronic devices.

The effect of SiC particle size (300, 600 and 1200 mesh) on the properties of 15 wt% SiC particles reinforced AlSi10Mg matrix composites fabricated by laser powder bed fusion (LPBF) was investigated. The results showed that the laser absorptivity of blended powder increased as the SiC particle size decreased, which was useful to improve the densification of the LPBFed composites. The highest relative density of 98.9% was obtained at 1200 mesh of SiC particle. The amount of the interfacial reaction products, including Al4SiC4 and Si, was increased with reducing the SiC particle size. For all type of the composites, SiC particles had a good wettability with the aluminum matrix owing to the high temperature and the interfacial reaction during the LPBF process. The mechanical properties were significantly improved by decreasing the SiC particles size. The microhardness of 316.1 HV0.2 and the ultimate compressive strength of 764.1 MPa were achieved using SiC particle having 1200 mesh size. The existence of the pores in the aluminum matrix and the SiC particle's cracking were the primary reasons for the failure of the composites. Furthermore, large SiC particles were more easily cracked. When the SiC particle size decreased from 300 mesh to 1200 mesh, the average coefficient of friction (COF) distinctly reduced from 0.45 to 0.18 and wear rate decreased from 9.09 to 2.02 × 10−4 mm3N−1m−1, respectively. The abrasive and adhesive wear were the dominant wear mechanism of the LPBFed composites with 300 mesh of SiC particle. However, as the SiC particle decreased to 1200 mesh, the main wear mechanism was transferred to the delamination and abrasive mechanism. These results are contributed to understanding the characteristics of LPBFed SiCp/AlSi10Mg composites.

A highly efficient and practical Ru-catalyzed direct C–H functionalization of indolines and N-alkylaniline with a simple pivaloyl as a directing group is developed. Broad substrate scopes with respect to N-heteroarenes and olefins are observed. The selective C7-position alkynylation for indoline also proceeds well by using inexpensive ruthenium as a catalyst, and pivaloyl as a directing group.

The multi-laser powder bed fusion (MLPBF) has attracted more and more attention due to high productivity and large area. However, thus far the distribution and evolution of the thermal stress with different laser beams are rarely investigated. A block-by-block numerical model considering the laser scanning strategy and part-scale was developed to study the residual stress in MLPBF. As the laser beam number increased from 1 to 4, the residual stress at the top surface of the part decreased but the internal residual stress at the bottom center of the part significantly increased. The average and maximum stresses increased with the laser beam number, indicating that the cracks were more likely to occur with an increase of the laser beam number. The residual stress in the multi-laser overlap area was reduced, resulting in an important influence on the residual stress distribution. More frequent tension-compression stress transitions occurred during MLPBF, and the compressive stress along the deposition direction had a more important influence when the laser beam number increased. The simulated results agreed well with the experimental data. The results of the study provide a significant understanding of the residual stress and are helpful to the process optimization in MLPBF.

We investigated the electronic properties of arsenene and antimonene heterobilayer under strain and external electric field by the first-principles calculation method. The appropriate biaxial strain(e = −5%) and E-field(E = −1.0 and 0.07 V A−1) of As/Sb bilayer convert the heterostructure from semiconductor to metal. The transition is caused by the sensitivity of the interlayer coupling and charge distribution on each layer of As/Sb heterobilayer. With the change of biaxial strain, the alterations of the orbital states in each layer present synchronous tendency. In contrast, the electronic occupation under E-field intensities is mostly contributed by the layer of Sb atoms. It is remarkable that a double-peak curve is occurred in band gaps as the function of intensities when negative E-field applied. The mechanism of tuning band structures affected by strain and electric field is also discussed.

The effect of the track length and track number on the evolution of the thermal variables and molten pool characteristics of selective laser melting alumunum alloy has been studied numerically and experimentally in this paper. It is found that as the track length increases, the maximum temperature, maximum heating rate and maximum cooling rate decrease first and then become stable. Both molten pool width and depth increase first, then keep stable and then increase a little at the end of the track. The molten pool lifetime increases first, then becomes stable, and then decreases at the end of the track. With the increase of the track’s number, the maximum temperature decreases first and then becomes stable. While, the molten pool width, depth and lifetime increase first and keep almost constant, the maximum heating rate and cooling rate are nearly same.

Rescanning has been introduced as a new method to improve the performance of selective laser melting (SLM) in recent years. However, many of the related works were done on the investigating of the rescanning parameters and only one rescanning cycle was used. In this work, the influences of rescanning cycle on the relative density, microstructure, residual stress and mechanical properties of SLMed Ti6Al4V alloy were investigated. The results show that as the rescanning cycles increase from 0 to 4, the relative density and residual stress of the samples increase at first and then decrease, the highest relative density and residual stress are found when the number of rescanning cycle is one. The number of rescanning cycle has little effect on the microstructure. The microstructures all consist of the martensitic α′ laths which grow inside the columnar prior β grains. The ultimate tensile strength (UTS), yield strength, micro-hardness and micro-strain of the samples all increase as the rescanning cycles increase from 0 to 3, but decrease when the samples are rescanned fourth times. This research provides an insight in the influence of rescanning cycles on characteristics of SLM process and can be used to optimize the process parameters of SLM.

Selective creation of quaternary carbon centers has been a long-standing challenge in synthetic chemistry. We report here the chromium-catalyzed, para-selective formation of arylated quaternary carbon centers by alkylative reactions of benzamide derivatives with tertiary alkylmagnesium bromides at room temperature. The reaction, which was enabled by a low-cost chromium(III) salt combined with trimethylsilyl bromide, introduces a sterically bulky tertiary alkyl scaffold on the para-position of benzamide derivatives in a highly selective fashion without either isomerization of the tertiary alkyl group or formation of ortho-alkylated byproducts. Forming low-valent Cr species in situ by reaction of CrCl3 with t-BuMgBr accompanied by evolution of hydrogen can be considered, which serves as reactive species to promote the reaction. The para-alkylation likely occurs via a radical-type nucleophilic substitution of imino-coordination benzimidate intermediate., The selective installation of quaternary carbon substituents on arenes is a highly challenging synthetic goal. Here, the authors report a chromium-catalyzed para-selective functionalization of benzamides with tertiary organometallic reagents under mild conditions.

A highly efficient and practical transition-metal-free CsOH/O2 catalyst system was developed for the N-alkylation of amines with alcohols under argon. This strategy was compatible with many alcohols and exhibits excellent functional group tolerance. More significantly, the selective formation of secondary amines was achieved in excellent yields. The detailed mechanistic study gave a clear understanding of the role of base and oxygen in the catalytic cycle.

Palladium-catalyzed oxalyl amide directed ortho-alkynylation of arylalkylamine derivatives is reported for the first time. A wide variety of β-arylethamine and γ-arylpropamine derivatives are compatible with this protocol. This method provides a general means to synthesize substituted alkynylarylalkylamine derivatives, highlighting the ability of oxalyl amide in promoting C-H functionalization at unique δ and ε positions.

The first Pd-catalyzed regioselective γ-carbonylation of oxalyl amide protected aliphatic amines with carbon monoxide leading to synthesis of pyrrolidones has been developed. Both γ-methyl and cyclopropyl methylene C–H bonds are well activated to obtain the corresponding pyrrolidones in moderate to excellent yields. The role of 3-(trifluoromethyl)benzoic acid as an additive is critical as it helps in stabilizing the palladium intermediate formed during the catalytic cycle. The reaction scope is extended to benzylamine and allyl amine derivatives, thereby affording the corresponding products in good to excellent yields.

A novel and efficient synthetic method for o-fluorobenzylamines via palladium catalyst using an easily accessible oxalyl amide as directing group has been developed. The cheap N-fluorobenzenesulfonimide could be used as an effective [F+] source and t-amyl-OH as the solvent with Pd(OAc)2 as catalyst. Selective mono- or difluorination of oxalyl amide-protected benzylamine derivatives were achieved by modifying the reaction conditions, which presented an efficient method for the preparation of ortho-fluorinated benzylamines.

Transition-metal-catalyzed direct site-selective functionalization of arene C–H bonds has emerged as an innovative approach for building the core structure of pharmaceutical agents and other versatile complex compounds. However, para-selective C–H functionalization has seldom been explored, only a few examples, such as steric-hindered arenes, electron-rich arenes, and substrates with a directing group, have been reported to date. Here we describe the development of a ruthenium-enabled para-selective C–H difluoromethylation of anilides, indolines, and tetrahydroquinolines. This reaction tolerates various substituted arenes, affording para-difluoromethylation products in moderate to good yields. Results of a preliminary study of the mechanism indicate that chelation-assisted cycloruthenation might play a role in the selective activation of para-CAr–H bonds. Furthermore, this method provides a direct approach for the synthesis of fluorinated drug derivatives, which has important application for drug discovery and development., Selective para-functionalization of substituted arenes is a formidable challenge in homogeneous catalysis. Here, the authors achieved the para-selective C-H difluoromethylation of anilides, indolines and tetrahydroquinolines with a ruthenium catalyst in good yields and apply it to the synthesis of bioactive compounds.

We investigate the transport properties of pristine zigzag-edged borophene nanoribbons (ZBNRs) of different widths, using the fist-principles calculations. We choose ZBNRs with widths of 5 and 6 as odd and even widths. The differences of the quantum transport properties are found, where even-N BNRs and odd-N BNRs have different current-voltage relationships. Moreover, the negative differential resistance (NDR) can be observed within certain bias range in 5-ZBNR, while 6-ZBNR behaves as metal whose current rises with the increase of the voltage. The spin filter effect of 36% can be revealed when the two electrodes have opposite magnetization direction. Furthermore, the magnetoresistance effect appears to be in even-N ZBNRs, and the maximum value can reach 70%., Comment: 11 pages, 9 figures

An easily synthesized and accessible N,O-bidentate auxiliary has been developed for selective C-H activation under palladium catalysis. The novel auxiliary showed its first powerful application in C-H functionalization of remote positions. Both C(sp(2))-H and C(sp(3))-H bonds at δ- and e-positions were effectively activated, thus giving tetrahydroquinolines, benzomorpholines, pyrrolidines, and indolines in moderate to excellent yields by palladium-catalyzed intramolecular C-H amination.