The first ring-opening reactions of ligated boriranes (boracyclopropanes) are described. Treatment of readily available NHC-boriranes bearing ester substituents on the borirane ring with HCl provides ...stable γ-NHC-bora-γ-lactones in isolated yields ranging from 40% to 73%. The reactions occur through 1,3-addition of HCl across a B–C bond of the NHC-borirane to form a ring-opened NHC-boryl chloride, followed by lactonization with chloride displacement. Experimental evidence suggests that both the borirane ring-opening reaction and the boralactonization reaction occur with inversion at boron.
Boron has been explored as p-block catalysts for nitrogen reduction reaction (NRR) by density functional theory. Unlike transition metals, on which the active centers need empty d orbitals to accept ...the lone-pair electrons of the nitrogen molecule, the sp3 hybrid orbital of the boron atom can form B-to-N π-back bonding. This results in the population of the N–N π* orbital and the concomitant decrease of the N–N bond order. We demonstrate that the catalytic activity of boron is highly correlated with the degree of charge transfer between the boron atom and the substrate. Among the 21 concept-catalysts, single boron atoms supported on graphene and substituted into h-MoS2 are identified as the most promising NRR catalysts, offering excellent energy efficiency and selectivity against hydrogen evolution reaction.
Covalent organic frameworks (COFs) are crystalline, highly porous, two- or three-dimensional polymers with tunable topology and functionalities. Because of their higher chemical stabilities in ...comparison to their boron-linked counterparts, imine or β-ketoenamine linked COFs have been utilized for a broad range of applications, including gas storage, heterogeneous catalysis, energy storage devices, or proton-conductive membranes. Herein, we report the synthesis of highly porous and chemically stable acetylene (−CC−) and diacetylene (−CC–CC−) functionalized β-ketoenamine COFs, which have been applied as photocatalyst for hydrogen generation from water. It is shown that the diacetylene moieties have a profound effect as the diacetylene-based COF largely outperforms the acetylene-based COF in terms of photocatalytic activity. As a combined effect of high porosity, easily accessible diacetylene (−CC–CC−) functionalities and considerable chemical stability, an efficient and recyclable heterogeneous photocatalytic hydrogen generation is achieved.
Facile interconversion between CO2 and formate/formic acid (FA) is of broad interest in energy storage and conversion and neutral carbon emission. Historically, electrochemical CO2 reduction reaction ...to formate on Pd surfaces was limited to a narrow potential range positive of −0.25 V (vs RHE). Herein, a boron-doped Pd catalyst (Pd–B/C), with a high CO tolerance to facilitate dehydrogenation of FA/formate to CO2, is initially explored for electrochemical CO2 reduction over the potential range of −0.2 V to −1.0 V (vs RHE), with reference to Pd/C. The experimental results demonstrate that the faradaic efficiency for formate (ηHCOO– ) reaches ca. 70% over 2 h of electrolysis in CO2-saturated 0.1 M KHCO3 at −0.5 V (vs RHE) on Pd–B/C, that is ca. 12 times as high as that on homemade or commercial Pd/C, leading to a formate concentration of ca. 234 mM mg–1 Pd, or ca. 18 times as high as that on Pd/C, without optimization of the catalyst layer and the electrolyte. Furthermore, the competitive selectivity ηHCOO–/ηCO on Pd–B/C is always significantly higher than that on Pd/C despite a decreases of ηHCOO– and an increases of the CO faradaic efficiency (ηCO) at potentials negative of −0.5 V. The density functional theory (DFT) calculations on energetic aspects of CO2 reduction reaction on modeled Pd(111) surfaces with and without H-adsorbate reveal that the B-doping in the Pd subsurface favors the formation of the adsorbed HCOO*, an intermediate for the FA pathway, more than that of *COOH, an intermediate for the CO pathway. The present study confers Pd–B/C a unique dual functional catalyst for the HCOOH ↔ CO2 interconversion.
The electrochemical reduction of CO2 to multi-carbon products has attracted much attention because it provides an avenue to the synthesis of value-added carbon-based fuels and feedstocks using ...renewable electricity. Unfortunately, the efficiency of CO2 conversion to C2 products remains below that necessary for its implementation at scale. Modifying the local electronic structure of copper with positive valence sites has been predicted to boost conversion to C2 products. Here, we use boron to tune the ratio of Cuδ+ to Cu0 active sites and improve both stability and C2-product generation. Simulations show that the ability to tune the average oxidation state of copper enables control over CO adsorption and dimerization, and makes it possible to implement a preference for the electrosynthesis of C2 products. We report experimentally a C2 Faradaic efficiency of 79 ± 2% on boron-doped copper catalysts and further show that boron doping leads to catalysts that are stable for in excess of ~40 hours while electrochemically reducing CO2 to multi-carbon hydrocarbons.
A variety of two-dimensional materials have been reported in recent years, yet single-element systems such as graphene and black phosphorus have remained rare. Boron analogues have been predicted, as ...boron atoms possess a short covalent radius and the flexibility to adopt sp(2) hybridization, features that favour the formation of two-dimensional allotropes, and one example of such a borophene material has been reported recently. Here, we present a parallel experimental work showing that two-dimensional boron sheets can be grown epitaxially on a Ag(111) substrate. Two types of boron sheet, a β12 sheet and a χ3 sheet, both exhibiting a triangular lattice but with different arrangements of periodic holes, are observed by scanning tunnelling microscopy. Density functional theory simulations agree well with experiments, and indicate that both sheets are planar without obvious vertical undulations. The boron sheets are quite inert to oxidization and interact only weakly with their substrate. We envisage that such boron sheets may find applications in electronic devices in the future.
We report the discovery of a rule-breaking two-dimensional aluminum boride (AlB6–ptAl–array) nanosheet with a planar tetracoordinate aluminum (ptAl) array in a tetragonal lattice by comprehensive ...crystal structure search, first-principles calculations, and molecular dynamics simulations. It is a brand new 2D material with a unique motif, high stability, and exotic properties. These anti-van’t Hoff/Le Bel ptAl-arrays are arranged in a highly ordered way and connected by two sheets of boron rhomboidal strips above and below the array. The regular alignment and strong bonding between the constituents of this material lead to very strong mechanical strength (in-plane Young’s modulus Y x = 379, Y y = 437 N/m, much larger than that of graphene, Y = 340 N/m) and high thermal stability (the framework survived simulated annealing at 2080 K for 10 ps). Additionally, electronic structure calculations indicate that it is a rare new material with triple Dirac cones, Dirac-like fermions, and node-loop features. Remarkably, this material is predicted to be a 2D phonon-mediated superconductor with T c = 4.7 K, higher than the boiling point of liquid helium (4.2 K). Surprisingly, the T c can be greatly enhanced up to 30 K by applying tensile strain at 12%. This is much higher than the temperature of liquid hydrogen (20.3 K). These outstanding properties may pave the way for potential applications of an AlB6–ptAl–array in nanoelectronics and nanomechanics. This work opens up a new branch of two-dimensional aluminum boride materials for exploration. The present study also opens a field of two-dimensional arrays of anti-van’t Hoff/Le Bel motifs for study.
Was considered a problem of an optimization of concurrent gas centrifuges for separation of Boron isotopes in form of trifluoride BF3. As the criteria was used a minimum of total number of gas ...centrifuges upon the given external parameters of the cascades' scheme. The method is based on the analytical relationships for the flows of stages, received under approximating minimization of the total feed flow. Conducted cascade calculations showed that it is possible to obtain BF3 with enrichment up to 99.9 % of 10B in the selection and up to 0.1 % in the waste, which is equivalent to 99.9 % of 11B.
•The trace angle of α laths has been defined according to orientation-trace method.•The morphology of α laths produced by 〈100〉 fiber texture has been investigated.•The transformed α laths form a ...cross configuration due to variant selection.
The microstructure morphology of transformed α is controlled by the crystallographic orientation of its parent β grain. In the fusion zone of an electron beam welded joint of TC25G titanium alloy, the columnar β grains exhibited a {001} 〈100〉 cube texture, in which four kinds of α laths with two main growth (trace line) directions formed after post-welded heat treatment. According to the numerical simulation by an orientation-trace method, the trace angle of α laths mainly distributed across the ranges of 40˚-60˚ and 120˚-140˚ in the β matrix with 〈001〉 fiber texture, thus the microstructure morphology of transformed α naturally tended to form cross configurations with two nearly perpendicular α laths.
Monodefluoroborylation of polyfluoroalkenes has been achieved in a regioselective manner under mild conditions via copper catalysis. The method has shown an extremely broad scope of substrates, ...including (difluorovinyl)arenes, tetrafluoroethylene (TFE), (trifluorovinyl)arenes, and trifluoromethylated monofluoroalkenes. The choice of boron source was important for the efficient transformation of (difluorovinyl)arenes; (Bpin)2 was suitable for substrates with an electron-deficient aryl group and (Bnep)2 for those with an electron-rich aryl group. Derivatization of the (fluoroalkenyl)boronic acid esters to the corresponding potassium trifluoroborate salts has rendered the products easily isolable, which greatly improved the synthetic practicality of the monodefluoroborylation reaction. Stoichiometric experiments indicate that the fate of the regioselectivity depends on the mode of β-fluorine elimination, which depends on the substrate. Further transformation of the boryl group has allowed facile preparation of fluoroalkene derivatives as exemplified by the synthesis of a fluoroalkene mimic of atorvastatin, which potently inhibited the enzyme activity of HMG-CoA reductase.
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