Boronic Functional Groups Research Articles

Enhanced electroproduction of hydrogen peroxide with oxidized boron-doped carbon catalysts synthesized from gaseous CO2

As an eco-friendly alternative to the conventional anthraquinone process, electrochemical production of hydrogen peroxide (H2O2) through the oxygen reduction reaction has been attracting attention. The goal of this work is to derive a carbon-based material from carbon dioxide (CO2) to achieve high performance in electrochemical H2O2 production. Doping heterogeneous element such as oxygen on a carbon catalyst has been mainly explored to increase the selectivity and activity, but little research has been conducted on enhancing catalytic activity with oxidized boron insertion. This study proposes porous carbon materials synthesized from CO2 as electrocatalysts. Polyethylene oxide (PEO) was thermally treated together to increase the boron-oxygen bonding sites. As a result, the synthesized carbon materials having oxidized boron functional groups of BC2O and BCO2 showed high activity (1.25 mA cm−2) and selectivity (∼90 %) over a wide voltage range in two-electron ORR (Oxygen Reduction Reaction) at alkaline media. Furthermore, in an H-cell where 0.4 V vs. RHE was applied, the average H2O2 production rate was maintained at 452.96 mmol g−1 h−1 for four hours with a high faraday efficiency of 90 %.

Effect of B2O3 on the structure, morphology, and electrochemical properties of hierarchical multilayer carbon nanofiber/MnO2/carbon nanofiber composites

One major challenge in capacitor development is achieving high capacitance and large energy density with rapid charge and discharge rates of minutes to seconds. This paper reports boron-containing trilayer structured MnO2/carbon nanofiber composites(PPMnB) as promising supercapacitor electrodes with high electrochemical properties under rapid charge and discharge conditions. Multilayer carbon nanofiber(CNF) composites are designed to maximize the advantages of CNF, MnO2, and boron functional groups when applying functionalized porous CNF containing transition metal composites to supercapacitor electrodes. The PPMnB electrode exhibits a high specific capacitance (215 Fg−1 at 1 mAcm−2), good rate capability (83 % capacity retention at 20 mAcm−2), high energy density (23.5 Whkg−1 at 400 Wkg−1), and good cycling stability (only 6.0 % loss after 10,000 cycles at 1 mAcm−2). In addition, the asymmetric capacitor of the PPMnB(25) and PPB(0) used as the positive and negative electrode shows excellent electrochemical performance, including an excellent energy density of 46.3 Whkg−1 at a maximum voltage of 1.4 V. High electrochemical performance is achieved through the combined effects of the hierarchical porosity of CNF, high electrochemical activity of MnO2, and increased electrical conductivity by boron functional groups in each layer.

Electrochemical activity of triple-layered boron-containing carbon nanofibers with hollow channels in supercapacitors

Triple-layered boron-containing carbon nanofibers (CNFs) with hollow channels (PPMPB) are fabricated via step-by-step electrospinning for high-performance freestanding supercapacitors. Polyacrylonitrile (PAN)-based CNFs in the first layer are chosen as the support layer material because of their excellent chemical stability and electrospinnability. The well-developed hollow channels provided fast ion diffusion in the second layer of PAN/poly(methyl methacrylate) (PMMA)-based CNFs. The surface boron functional groups constituting the third layer contribute to the pseudo-capacitance. The symmetric supercapacitor of the PPMPB electrodes delivers a maximum specific capacitance of 180 Fg−1 at 1 mAcm−2, a high energy density of 22.38 Whkg−1 at a power density of 400 Wkg−1, and an excellent retention rate of 96% after 10,000 cycles in aqueous solution. The excellent electrochemical performance is attributed to the unique sandwich nanostructure with a three-layer structure, in which the factors representing the electrochemical properties of each layer do not interfere with each other. Therefore, a moderate amount of boron and the high surface area of the triple-layer structured PPMPB can be fully utilized as an excellent conductive network and electroactive sites, which is expected in a high-performance supercapacitor electrode.

The Boron Advantage: The Evolution and Diversification of Boron's Applications in Medicinal Chemistry.

In this review, the history of boron’s early use in drugs, and the history of the use of boron functional groups in medicinal chemistry applications are discussed. This includes diazaborines, boronic acids, benzoxaboroles, boron clusters, and carboranes. Furthermore, critical developments from these functional groups are highlighted along with recent developments, which exemplify potential prospects. Lastly, the application of boron in the form of a prodrug, softdrug, and as a nanocarrier are discussed to showcase boron’s emergence into new and exciting fields. Overall, we emphasize the evolution of organoboron therapeutic agents as privileged structures in medicinal chemistry and outline the impact that boron has had on drug discovery and development.

A radical approach for the selective C-H borylation of azines.

Boron functional groups are often introduced in place of aromatic carbon-hydrogen bonds to expedite small-molecule diversification through coupling of molecular fragments1-3. Current approaches based on transition-metal-catalysed activation of carbon-hydrogen bonds are effective for the borylation of many (hetero)aromatic derivatives4,5 but show narrow applicability to azines (nitrogen-containing aromatic heterocycles), which are key components of many pharmaceutical and agrochemical products6. Here we report an azine borylation strategy using stable and inexpensive amine-borane7 reagents. Photocatalysis converts these low-molecular-weight materials into highly reactive boryl radicals8 that undergo efficient addition to azine building blocks. This reactivity provides a mechanistically alternative tactic for sp2 carbon-boron bond assembly, where the elementary steps of transition-metal-mediated carbon-hydrogen bond activation and reductive elimination from azine-organometallic intermediates are replaced by a direct, Minisci9-style, radical addition. The strongly nucleophilic character of the amine-boryl radicals enables predictable and site-selective carbon-boron bond formation by targeting the azine's most activated position, including the challenging sites adjacent to the basic nitrogen atom. This approach enables access to aromatic sites that elude current strategies based on carbon-hydrogen bond activation, and has led to borylated materials that would otherwise be difficult to prepare. We have applied this process to the introduction of amine-borane functionalities to complex and industrially relevant products. The diversification of the borylated azine products by mainstream cross-coupling technologies establishes aromatic amino-boranes as a powerful class of building blocks for chemical synthesis.

Silylboranes as Powerful Tools in Organic Synthesis: Stereo- and Regioselective Reactions with 1,n-Enynes

Bismetalated alkenes, accessible by element–element addition to alkynes, are valuable building blocks in organic synthesis, providing wide opportunities for divergent synthesis. Silaboration of alkynes with a pendant olefinic group, catalyzed by group 10 metal complexes, and subsequent transformation of the silicon and boron functional groups give access to densely functionalized 1,3-dienes and 1,3,5-trienes with defined stereo- and regiochemistry, 1,2-dienes, and carbocyclic and heterocyclic products.1 Introduction2 Background3 Reactions with 1,3-Enynes4 Cyclization 1,6-Enynes5 Cyclization 1,7-Enynes6 Cyclization of 1,n-Enynes (n > 7)7 Cyclization of Dienynes and Enediynes8 Cyclization of 1,6-Diynes9 Conclusions

Boron doping and structure control of carbon materials for supercapacitor application: the effect of freeze-drying and air-drying for porosity engineering

In the present work, we demonstrate a strategy of combining boron doping and porosity engineering for a highly modulated carbon component and pore structure, in which two contrasting drying methods (air-drying, freeze-drying) and their effects on supercapacitor performance are investigated in detail. Under freeze-drying and air-drying conditions, carbon nanoparticles and nanosheets are obtained, respectively. It is revealed that the carbon nanoparticles exhibit higher porosity (BET surface area of 1275 m2 g−1 and pore volume of 2.64 cm3 g−1) than the nanosheets (BET surface area of 1109 m2 g−1 and pore volume of 1.72 cm3 g−1); however, the boron content of the nanoparticles is lower (0.82 at.%) than that of the nanosheets (1.66 at.%). In the freeze-drying process, the direct sublimation of ice can prevent pore collapse, whereas stacking of nanosheets via Van der Waals interactions occurs during the air-drying process. With the air-drying method, the B-O-B structures produced by the evaporation process preferentially react with carbon, which promotes the production of more boron functional groups. As a result, the capacitive measurement indicates that the carbon nanoparticle electrode delivers larger capacitance of 129 F g−1 at 1 A g−1 and higher energy density of 41 Wh kg−1 in the two-electrode system, in contrast to those of the nanosheets (capacitance of 98 F g−1 and energy density 31 Wh kg−1) using EMIMBF4/AN as electrolyte. This kind of effect of freeze-drying and air-drying for porosity engineering is probably helpful for further supercapacitor applications.

Enhanced electrochemical properties of boron functional groups on porous carbon nanofiber/MnO2 materials

Heteroatoms (B, N, O)-containing porous manganese oxide (MnO2)/carbon nanofiber (MnB-CNF) materials are prepared by one-step electrospinning method via polyacrylonitrile (PAN) and manganese(II) chloride (MnCl2) in dimethylformamide (DMF) solution containing different concentrations of B2O3. The MnB-CNF electrode exhibits optimized electrochemical behavior with a high energy density of 22.6Whkg−1 at a power density of 400Wkg−1 and a specific capacitance range of 210–160Fg−1 in the discharge current density range of 1.0 to 20mAcm−2 in aqueous KOH electrolyte. The higher electrochemical performance of MnB-CNF as a result of the electrochemical double-layer capacitor (EDLC), compared to regular Mn-CNF without B-based functional groups, is attributed to well-balanced meso- and micropores affecting the easy adsorption and transport of electrolyte ions, in addition to the pseudocapacitive redox reactions from MnO2, N, O, and extra numerous B in alkaline electrolytes. Thus, tailoring the pore structures with proper specific surface area, pore size, and number of heteroatoms is crucial for optimizing their electrochemical properties in the combined efforts to develop EDLCs and pseudocapacitance.

(11)B Solid-State NMR Interaction Tensors of Linear Two-Coordinate Boron: The Dimesitylborinium Cation.

Borinium cations (R2B(+)) are of particular fundamental and applied interest in part due to their pronounced Lewis acidity which enables unique chemical transformations. Solid-state NMR spectroscopy of magic-angle spinning and stationary powdered samples of the dicoordinate boron cation in the recently reported dimesitylborinium tetrakis(pentafluorophenyl)borate compound (Shoji et al. Nature Chem. 2014, 6, 498) is applied to characterize the (11)B electric field gradient (EFG) and chemical shift (CS) tensors. The experimental data are consistent with linear C-B(+)-C geometry. The (11)B quadrupolar coupling constant, 5.44 ± 0.08 MHz, and the span of the CS tensor, 130 ± 1 ppm, are both particularly large relative to literature data for a variety of boron functional groups, and represent the first such data for the linear C-B(+)-C borinium moiety. The NMR data are similar to those for the neutral tricoordinate analogue, trimesitylborane, but contrast with those of the Cp*2B(+) cation. Quantum chemical calculations are applied to provide additional insights into the relationship between the NMR observables and the molecular and electronic structure of the dimesitylborinium cation.

Boron/nitrogen co-doped helically unzipped multiwalled carbon nanotubes as efficient electrocatalyst for oxygen reduction.

Bamboo structured nitrogen doped multiwalled carbon nanotubes have been helically unzipped, and nitrogen doped graphene oxide nanoribbons (CNx-GONRs) with a multifaceted microstructure have been obtained. CNx-GONRs have then been codoped with nitrogen and boron by simultaneous thermal annealing in ammonia and boron oxide atmospheres, respectively. The effects of the codoping time and temperature on the concentration of the dopants and their functional groups have been extensively investigated. X-ray photoelectron spectroscopy results indicate that pyridinic and BC3 are the main nitrogen and boron functional groups, respectively, in the codoped samples. The oxygen reduction reaction (ORR) properties of the samples have been measured in an alkaline electrolyte and compared with the state-of-the-art Pt/C (20%) electrocatalyst. The results show that the nitrogen/boron codoped graphene nanoribbons with helically unzipped structures (CNx/CBx-GNRs) can compete with the Pt/C (20%) electrocatalyst in all of the key ORR properties: onset potential, exchange current density, four electron pathway selectivity, kinetic current density, and stability. The development of such graphene nanoribbon-based electrocatalyst could be a harbinger of precious metal-free carbon-based nanomaterials for ORR applications.

Suzuki Polycondensation toward High Molecular Weight Poly(m-phenylene)s: Mechanistic Insights and End-Functionalization

Synthesis of a poly(m-phenylene) by Suzuki polycondensation (SPC) using an AB-type m-phenylene monomer is reported (A and B refer to bromo and boron functional groups, respectively). Despite the attempted high molecular weight products, SPC under the conventional conditions using Pd[P(p-Tol)3]3 as catalyst gave rise to oligomeric products only. They comprise cycles and several series of open-chain poly(m-phenylene)s with various end group patterns. These patterns were caused by side reactions such as ligand scrambling. Buchwald’s SPhos ligand was therefore alternatively employed for high turnover catalysis to accelerate SPC over such detrimental side reactions. This modification indeed led to the formation of high molecular weight products ∼40 kDa (DP ∼ 210), while oligomeric cyclic products still remained prominent. Cycle formation could, however, drastically be reduced by slow monomer addition. SPC was also performed in the presence of an excess monofunctional compound, R–A or R–B. The molecular weights...

Synthesis and NMR studies of the polymer membranes based on poly(4-vinylbenzylboronic acid) and phosphoric acid

Proton conduction in novel anhydrous membranes based on host polymer, poly(4-vinylbenzylboronic acid), (P4VBBA) and phosphoric acid, (H3PO4) as proton solvent was studied. The materials were prepared by the insertion of the proton solvent into P4VBBA at different stoichiometric ratios to get P4VBBA·xH3PO4 composite electrolytes. Homopolymer and the composite materials were characterized by FT-IR, 11B MAS NMR and 31P MAS NMR. 11B MAS NMR results suggested that acid doping favors or leads to a four-coordinated boron arrangement. 31P MAS NMR results illustrated the immobilization of phosphoric acid to the polymer through condensation with boron functional groups (B–O–P and/or B–O–P–O–B). Thermogravimetric analysis (TGA) showed that the condensation of composite materials starts approximately at 140°C. An exponential weight loss above this temperature was attributed to intermolecular condensation of acidic units forming cross-linked polymer. The insertion of phosphoric acid into the matrix softened the materials shifting Tg to lower temperatures. The temperature dependence of the proton conductivity was modeled with Arrhenius relation. P4VBBA·2H3PO4 has a maximum proton conductivity of 0.0013S/cm at RT and 0.005S/cm at 80°C.

New polyphenylene-based macromolecular architectures by using well defined macromonomers synthesized via controlled polymerization methods

Recent advances have led to the development of a range of methods for the synthesis of finely engineered poly( p-phenylene)s (PPPs) having improved solubility and film-forming properties. The present article describes recent directions in the preparation of PPPs with various polymeric side-chains. It is possible to prepare PPP graft copolymers with complex macromolecular architectures by the use of macromonomers prepared by controlled polymerization routes, namely atom transfer radical polymerization or ring opening polymerization and may contain either bromine or the ester boronic functional groups, both useful, for example, in Suzuki polycondensation or Yamamoto coupling. The new tailored structures of PPP graft copolymers may find applications in various areas, including use as light emitting diodes or sensing devices.