Latest ArticlesA rhodium/diphosphine-catalyzed asymmetric cross-dehydrogenative coupling between sulfoximines and dihydrosilanes has been achieved. This is the first report on the enantioselective N-silylation of sulfoximines. The protocol gives access to a variety of Si-stereogenic N-silylated sulfoximines in decent yield (up to 99%) with excellent stereoselectivity (up to 99%), featuring high atom economy, and a cleaner manner with H2 as the sole byproduct. The obtained bis-Si-stereogenic monohydrosilane product can be further converted into the corresponding chiral polymer with pendant sulfoximine groups.
In an era where the concept of green development is deeply rooted, magnesium (Mg) alloy as a light metal has a long-term development prospect in the process of energy saving, emission reduction and environmental improvement. However, anti-corrosion performance of Mg alloy is poor due to the high chemical activity and low equilibrium potential, which limits the development of Mg alloy products. Herein, three-dimensional mesopore hollow polypyrrole spheres (MHPS) were prepared, and the MHPS was inserted into the middle of the stacked hexagon boron nitride (h-BN) lamellae, which allowed the h-BN to be separated forming a further composite with abundant pore structure. Subsequently, the MHPS/h-BN-OH composite was uniformly sprayed on the Mg alloy surface via simple spraying method to form the superhydrophobic surface (SHS). Finally, the slippery liquid infused porous surface (SLIPS) was successfully fabricated by applying drops of silicone lubricant on the superhydrophobic coating surface. After a series of characterization and testing, the results showed that the stacking of h-BN lamellae was significantly reduced after h-BN was successfully embedded by MHPS. In addition, the fabricated SLIPS have excellent self-cleaning, mechanical stability, anti-icing and anti-corrosion properties. Therefore, the method of embedding polymer microspheres not only offers a new strategy for h-BN exfoliation, but also the successful prepared SLIPS largely retards the corrosion of Mg alloy while providing new ideas for the development of SLIPS.
Electrochemical conversion of nitrate (NO3−) to ammonia (NH3) can target two birds with one stone well, in NO3−-containing sewage remediation and sustainable NH3 production. However, single metal-based catalysts are difficult to drive high-efficient NO3− removal due to the multi-electron transfer steps. Herein, we present a tandem catalyst with simple structure, Cu-Co binary metal oxides (Cu-Co-O), by engineering intermediate phases as catalytic active species for NO3− conversion. Electrochemical evaluation, X-ray photoelectron spectroscopy, and in situ Raman spectra together suggest that the newly-generated Cu-based phases was prone to NO3− to NO2− conversion, then NO2− was reduced to NH3 on Co-based species. At an applied potential of −1.1 V vs. saturated calomel electrode, the Cu-Co-O catalyst achieved NO3−-N removal of 90% and NH3 faradaic efficiency of 81% for 120 min in 100 mL of 50 mg/L NO3−-N, consuming only 0.69 kWh/mol in a two-electrode system. This study provides a facile and efficient engineering strategy for developing high-performance catalysts for electrocatalytic nitrate conversion.
Sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) are the most promising alternatives to lithium-ion batteries, and thus have drawn intensive research attention. Porous carbon materials from different precursors have been widely used as anode materials owing to their compatible storage effectiveness of both larger radii sodium and potassium ions. However, the differential bonding behaviors of Na and K ions with porous carbon-based anode are the significant one worth investigating, which could provide a clean picture of alkali ions storage mechanism. Therefore, in this work, we prepare a porous carbon network derived from sawdust (SDC) wastes, to further analyze the differences on sodium and potassium ions storage behaviors in terms of bond-forming process. It is found that, as-prepared SDC anodes could deliver stable sodium and potassium storage capacities, however, there are notable distinctions in terms of electrochemical behaviors and diffusion processes. By virtue of ex-situ XRD and Raman spectroscopy, the phase transition reaction of potassium ions could be well-observed, and the results shows that the multiple intercalated compounds was formed in SDC network during ions insertion, further resulting in slower diffusion kinetics and larger resistance compared to non-bonded process of sodium ions storage. This study provides more insights into the differences between sodium and potassium ions storage, as well as the energy storage mechanism of porous carbon as anodes for secondary batteries.
A facile TfOH-catalyzed oxidative cyclization of allyl compounds and isocyanide has been developed with the assistance of DDQ, where isocyanide is used as the crucial "N" and "CN" sources. Highly functionalized 2-cyanopyrroles are constructed efficiently through a new formal [3 + 2] mode, demonstrating diverse reactivity and synthetic utility in organic chemistry. 2-Cyanopyrrole is converted into a nucleobase analogue of Remdesivir and 5H-pyrrolo[2, 1-a]isoindole through a three-step or a two-step sequence, respectively. This protocol features broad substrate scope, operational simplicity and good functional group tolerance.
Palladium-exchanged chabazite (Pd-CHA) zeolites as passive NOx adsorbers (PNAs) enable efficient purification of nitrogen oxides (NOx) in cold-start diesel exhausts. Their commercial application, however, is limited by the lack of facile preparation method. Here, high-performance CHA-type Pd-SAPO-34 zeolite was synthesized by a modified solid-state ion exchange (SSIE) method using PdO as Pd precursor, and demonstrated superior PNA performance as compared to Pd-SAPO-34 prepared by conventional wet-chemistry strategies. Structural characterization using Raman spectroscopy and X-ray diffraction revealed that the SSIE method avoided water-induced damage to the zeolite framework during Pd loading. Mechanistic investigations on the SSIE process by in situ infrared spectroscopy and X-ray photoelectron spectroscopy disclosed that, while PdO precursor was mainly converted to Pd2+ cations coordinated to the zeolite framework by consuming the -OH groups of the zeolite, a portion of PdO could also undergo thermal decomposition to form highly dispersed Pd0 clusters in the pore channels. This simplified and scalable SSIE method paves a new way for the cost-effective synthesis of defect-free high-performance Pd-SAPO-34 zeolites as PNA catalysts.
2-Hydroxycarbazole and 4-hydroxycarbazole are important chemicals with extensive applications in optoelectronic materials and pharmaceutical field. State of the art yield of 2-hydroxycarbazole is ~30% and the reaction time is typically in hours or days. Herein, we developed a green route for the continuous and high-throughput synthesis of 2-hydroxycarbazole and 4-hydroxycarbazole via photochemical intramolecular cyclization of 3‑hydroxy-2′‑chloro-diphenylamine using a self-designed millimeter scale photoreactor, which was designed based on sizing-up and numbering-up strategies for a decent liquid holdup (6.8 mL) and fabricated via femtosecond laser engraving technique. The photochemical synthesis was carried out continuously under the illumination of 365 nm UV-LED with dimethyl sulfoxide as solvent and potassium t-butoxide as catalyst. It was found that under optimized conditions a 2-hydroxycarbazole yield of 31.6% and a 4-hydroxycarbazole yield of 11.1% were obtained with a residence time of 1 min. Compared to semi-batch operations, the reaction time was shortened by 1–2 orders of magnitude. As a result, a throughput of 11.3 g/day 2-hydroxycarbazole and 4.0 g/day 4-hydroxycarbazole can be achieved from the photoreactor. It was proposed that the short reaction time and high product yield are resulted from higher photon transfer rates and more uniform photon distribution provided by the millimeter scale photoreactor, which enhances the reaction rates and mitigates overreaction.
Doyle-Kirmse rearrangement reactions have received continuous attention as an important method for constructing complex chemical structures. Herein, we disclosed an efficient rhodium-catalyzed Doyle-Kirmse rearrangement reaction, which can simultaneously construct CC bonds and CX (X = S/Se) bonds using sulfoxonium ylides as starting materials to obtain sulfur- or selenium-containing compounds. This strategy is characterized by the safer and greener carbene precursor, high yields and broad substrate scope, possessing a wide range of application.
Single-emitter white organic light-emitting diode (WOLED) based on small organic molecule exhibits great potential in simplifying fabrication process of WOLEDs. However, the design and synthesis of molecule for highly efficient single-emitter WOLED still remains a challenge. Herein, two asymmetric donor-acceptor-acceptor' (D-A-A') type molecule (PTZ-PQ-F and PTZ-PQ-CF3) are developed by employing trifluoromethyl (CF3) or fluorine atom as secondary acceptor, which can exhibit white lighting with dual emission bands consisting of blue traditional fluorescence from quasi-axial (ax) conformer and orange thermally activated delayed fluorescence (TADF) from quasi-equatorial (eq) conformer. The introduction of CF3 into PTZ-PQ-CF3 greatly enhanced the photoluminescence quantum yield (PLQY) by suppressing the nonradiative deactivation. Owing to electron-inductive-effect of CF3, the "eq" conformer of PTZ-PQ-CF3 exhibits a much smaller ΔEST of 0.01 eV to realize more efficient reverse intersystem crossing (RISC) process, and then enhance the exciton utilization (nearly 100%) of the whole dual emission system. Consequently, single-emitter WOLEDs based on PTZ-PQ-CF3 show nearly standard white emission with EQE of 13.0% and CIE of (0.35, 0.36) in mCP host and show warm white emission with high EQE of 25.5% and CIE of (0.40, 0.47) in 35 DczPPy host, which are the best performance among reported single-emitter WOLEDs.
High-temperature proton exchange membranes (HT-PEMs) possess excellent thermal and outstanding electrochemical stability, providing an avenue to realize high-temperature proton exchange membranes fuel cells (HT-PEMFCs) with both superior power density and long-term durability. Unfortunately, polybenzimidazole (PBI), a typical material for conventional HT-PEMs, fails to compromise the high nonaqueous proton conductivity and high mechanical properties, thus hindering their practical applications. Achieving efficient nonaqueous proton conduction is crucial for HT-PEMFC, and many insightful research works have been done in this area. However, there still lacks a report that integrates the host-guest interactions of phosphoric acid doping and the structural stability of polymers to systematically illustrate modification strategies. Here, we summarize recent advancements in enhancing the nonaqueous proton conduction of HT-PEMs. Various polymer structure modification strategies, including main chain and side group modification, cross-linking, blocking, and branching, are reviewed. Composite approaches of polymer, including compounding with organic porous polymers, filling the inorganic components and modifying with ionic liquids, etc., are also covered in this work. These strategies endow the HT-PEMs with more free volume, nanophase-separated structure, and multi-stage proton transfer channels, which can facilitate the proton transportation and improve their performance. Finally, current challenges and future directions for further enhancements are also outlined.
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