Over the last decade, 1,2‐metallate rearrangement of boronate complex has been dominating the literature of organoboron chemistry for the construction of very important C−C and C−boron bonds. Owing ...to the coordinative unsaturated nature of the boron atom, a nucleophile can attack on boron center for the formation of a boronate complex, which triggers 1,2‐migration under electrophilic activation at the α‐carbon. Apart from using stochiometric electrophilic activating reagents, several catalytic methods using transition metals in the presence or absence of light have been reported. The 1,2‐migration of boronate complexes allows synthesis of many different classes of racemic and chiral compounds including a wide range of substituted heterocycles. Synthesis of chiral and achiral substituted heterocycles by using 1,2‐metallate rearrangement of boronate complexes has been extensively reported by several groups owing to its prevalence in medicinal chemistry. This minireview highlights the methods known to date for the synthesis of heteroaryls by using 1,2‐migration of boronate complexes, organized in a chronological manner.
Migrations with boron: The 1,2‐migration of boronate complexes allows synthesis of many different classes of racemic and chiral compounds including a wide range of substituted heterocycles. This minireview highlights the methods known to date for the synthesis of heteroaryls by using 1,2‐migration of boronate complexes, organized in a chronological manner.
Unexpected phenomena displayed by low-boron-doped diamond (BDD) electrodes are disclosed in the present work. Generally, the presence of sp2 nondiamond carbon impurities in BDD electrodes causes ...undesirable electrochemical properties, such as a reduced potential window and increased background current, etc. However, we found that the potential window and redox reaction in normally doped (1%) BDD and low-doped (0.1%) BDD exhibited opposite tendencies depending on the extent of sp2 carbon. Moreover, we found that contrary to the usual expectations, low-doped BDD containing sp2 carbon hinders electron transfer, whereas in line with expectations, normally doped BDD containing sp2 exhibits enhanced electron transfer. Surface analyses by X-ray/ultraviolet photoelectron spectroscopy (XPS/UPS) and electrochemical methods are utilized to explain these unusual phenomena. This work indicates that the electrochemical properties of low-doped BDD containing sp2 might be due partially to the high level of surface oxygen, the large work function, the low carrier density, and the existence of different types of sp2 carbon.
In searching for alternative oxygen evolution reaction (OER) catalysts for acidic water splitting, fast screening of the material intrinsic activity and stability in half‐cell tests is of vital ...importance. The screening process significantly accelerates the discovery of new promising materials without the need of time‐consuming real‐cell analysis. In commonly employed tests, a conclusion on the catalyst stability is drawn solely on the basis of electrochemical data, for example, by evaluating potential‐versus‐time profiles. Herein important limitations of such approaches, which are related to the degradation of the backing electrode material, are demonstrated. State‐of‐the‐art Ir‐black powder is investigated for OER activity and for dissolution as a function of the backing electrode material. Even at very short time intervals materials like glassy carbon passivate, increasing the contact resistance and concealing the degradation phenomena of the electrocatalyst itself. Alternative backing electrodes like gold and boron‐doped diamond show better stability and are thus recommended for short accelerated aging investigations. Moreover, parallel quantification of dissolution products in the electrolyte is shown to be of great importance for comparing OER catalyst feasibility.
Ir‐black in back: Fast screening of the material intrinsic activity and stability profiles for acidic oxygen evolution reaction catalysts are of vital importance, but conclusions on the catalyst stability are commonly drawn on the basis of electrochemical information alone. Herein important limitations of such approaches, which are related to the degradation of the backing electrode material, are demonstrated. Ir‐black catalysts are investigated for OER activity and the dissolution behavior is found to depend on the backing electrode material used.
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•Electrochemical oxidation of pharmaceutical drug aspirin is investigated on PbO2, BDD and porous Ti/BDD electrodes.•Oxidation mechanism involving direct and indirect electrochemical ...oxidation is assessed.•Porous Ti/BDD electrode exhibits the best electrochemical performance.•The utilization rate of hydroxyl radicals on different electrodes is researched.•Oxidation activity is associated with nature characteristic and structure of the electrode material.
The electrochemical abatement of aspirin, a representative anti-inflammatory drug, is carried out through anodic oxidation by employing PbO2, boron-doped diamond (BDD) and porous Ti/BDD as anodes. The effect of nature characteristic and structure of the electrode material on the electrochemical oxidation is systematic investigated. The redox behavior of aspirin on different electrodes is studied by linear sweep voltammetry. Completely mineralization of aspirin could be achieved on BDD electrodes. The results show that the electrochemical incineration of aspirin on three electrodes follows a pseudo first-order kinetics behavior with apparent rate constant of 0.051, 0.185 and 0.367h−1 for PbO2, flat BDD and porous BDD electrode. Electrochemical degradation mechanism on BDD electrodes involves the direct and indirect electrochemical oxidation while there is only indirect oxidation for aspirin on PbO2 electrode. Porous Ti/BDD presents the best excellent electrochemical oxidation ability for aspirin compared with flat BDD and PbO2 electrode. The discrepancy of electrochemical oxidation could be explained in terms of in situ generation and utilization rate of hydroxyl radicals on the surface of electrode materials.
A copper‐catalyzed three‐component coupling of allenes, bis(pinacolato)diboron, and imines allows regio‐, chemo‐, and diastereoselective assembly of branched α,β‐substituted‐γ‐boryl homoallylic ...amines, that is, products bearing versatile amino, alkenyl, and borane functionality. Alternatively, convenient oxidative workup allows access to α‐substituted‐β‐amino ketones. A computational study has been used to probe the stereochemical course of the cross‐coupling.
A triumvirate: Copper‐catalyzed three‐component couplings of allenes, B2pin2, and imines furnish functionalized homoallylic amines, or Mannich‐type products, after oxidative workup. The process utilizes a commercially available copper catalyst, tolerates a range of allene and imine substrates, and affords complex products in high yield with high regio‐ and diastereocontrol. Computational studies were employed to understand the stereochemical course of the cross‐coupling.
Transition‐metal borides (TMBs) have recently attracted attention as excellent hydrogen evolution (HER) electrocatalysts in bulk crystalline materials. Herein, we show for the first time that VB and ...V3B4 have high electrocatalytic HER activity. Furthermore, we show that the HER activity (in 0.5 m H2SO4) increases with increasing boron chain condensation in vanadium borides: Using a −23 mV overpotential decrement derived from −0.296 mV (for VB at −10 mA cm−2 current density) and −0.273 mV (for V3B4) we accurately predict the overpotential of VB2 (−0.204 mV) as well as that of unstudied V2B3 (−0.250 mV) and hypothetical “V5B8” (−0.227 mV). We then derived an exponential equation that predicts the overpotentials of known and hypothetical VxBy phases containing at least a boron chain. These results provide a direct correlation between crystal structure and HER activity, thus paving the way for the design of even better electrocatalytic materials through structure–activity relationships.
HER best phase: Highly crystalline single phases of VB (CrB‐type structure) and V3B4 (Cr3B4‐type structure) are synthesized by arc‐melting. All the phases have high electrocatalytic hydrogen evolution reaction (HER) activities. A structure–activity relationship is found in the V‐B system that helps to predict new phases, their structures, and HER overpotentials.
Lithium-rich layer oxides can possess satisfactory specific capacity but suffer from severe voltage attenuation and poor cycle stability. In this work, Al-B dual-doping technique is introduced to ...modify Li-rich layered oxide cathode materials. Cross-section scanning electron microscopy, Energy Disperse Spectroscopy and X-ray photoelectron spectroscopy results confirm that Al and B successfully doped into the interior of the bulk Li1.2Ni0.2MnO2 particles, and the High-resolution transmission electron microscopy and X-ray diffraction Rietveld refinement results reveal that the c-axis distance of LMR-AB increases. The Al-B co-doped sample shows greatly enhanced electrochemical performance. Specifically, it exhibits of a discharge capacity of 120 mAh g−1 at 5 C and a capacity retention of 89.12% after 100 cycles at 1 C. The voltage decay is also greatly alleviated. The enhanced electrochemical performance of LMR-AB is due to the synergistic effects bought by the Al-B dual-doping, where increase of c-axis distance decreases Li+ intercalation/deintercalation barrier. B3+ doping into the tetrahedral site block the migration of TM ions and Al3+ act as pillars in the octahedral site, stabilizing the structure and suppressing the phase transition during cycling.
Cyclic diboranes(4) based on a chelating monoanionic benzylphosphine linker were prepared through boron–silicon exchange between arylsilanes and B2Br4. Coordination of Lewis bases to the remaining ...sp2 boron atom yielded unsymmetrical sp3‐sp3 diboranes, which were reduced with KC8 to their corresponding trans‐diborenes. These compounds were studied with a combination of spectroscopic methods, X‐ray diffraction, and DFT calculations. PMe3‐stabilized diborene 6 was found to undergo thermal rearrangement to gem‐diborene 8. DFT calculations on 8 reveal a polar boron–boron bond, and indicate that the compound is best described as a borylborylene.
Unsymmetrical diborenes were prepared through reduction of cyclic diboranes(4) containing a benzylphosphine bridge. A doubly phosphine‐stabilized diborene underwent an unprecedented, thermally induced rearrangement to form a borylborylene.
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