Iron(II) Bis-CNN Pincer Complex-Catalyzed Cyclic Carbonate Synthesis at Room Temperature

A series of unsymmetrical pyridine-bridged bis-pincer-type iron­(II) complexes were synthesized, and the complexes were used as catalysts for the cycloaddition of CO₂ and epoxides. At ambient temperature, the combined use of iron complexes and tetrabutyl ammonium bromide (TBAB) resulted in an efficient catalytic system for the synthesis of cyclic carbonates under low CO₂ pressure (0.5 MPa) and solvent-free conditions. More importantly, in the absence of TBAB, propylene oxide was also easily converted to the target products when the temperature was increased to 100 °C, and a turnover frequency (TOF) value of 7900 h^–1 was achieved at 120 °C. An elevated reaction temperature (80 °C) was required to achieve high conversion of challenging internal epoxides and oxetanes to their respective carbonates with good yields. Moreover, the iron catalyst can be easily recycled six times via simple filtration without any <b>s</b>ignificant loss of activity

Influence of Brönsted Acid Sites on Activated Carbon-Based Catalyst for Acetylene Dimerization

Activated carbon (AC) has been widely used as a support material with both tunable acidity and abundant functional groups for solid acid catalysts in various chemical processes such as acetylene dimerization. A facile, mild acid modification method that directly activates AC to generate rich defects and oxygen functional group surface structures with Brönsted acid sites and an enhanced conductivity is presented here. Impressively, the catalyst with optimized Brönsted acid sites and an enhanced dispersion of active components exhibited a superior acetylene dimerization catalytic activity. Moreover, theoretical calculations indicated that an increase in hydrogen concentration could inhibit the formation of coke. This research offered a feasible potential way to devise and construct a carbon-based solid acid catalyst with an excellent catalytic performance

A Flocculation–Adsorption Self-Coupled System for Wastewater Treatment with the Aim of Water Reuse

In this work, a unique flocculation–adsorption self-coupled system with a tunable coupling ratio is constructed based on an ultra-salt-sensitive polymer (USSP). USSP exhibits unique ultra-salt-sensitive properties, and distinct phase transition can be observed at a very low salt concentration of 30 g/L, which provides a straightforward strategy for coupling flocculation and adsorption processes. The self-coupling ratio between flocculation and adsorption can be finely controlled by adjusting the external stimuli. USSP shows a high adsorption capacity for the anionic dye (991.7 mg/g) in a short contact time (5 min) through the unique self-coupled flocculation–adsorption mechanism. More importantly, stimulus-triggered self-cleaning behavior of USSP can be achieved by a flocculation–adsorption self-coupled system, thereby minimizing the residual flocculant in treated water. Wastewater and salt can be easily reclaimed and reused for three cycles without any post-processing, which minimizes the total salt and water consumption in the textile dyeing industry

Dynamic event-triggered disturbance rejection control for speed regulation of networked PMSM

This article investigates the robust control problem for speed regulation of networked permanent magnet synchronous motor subject to the limited communication bandwidth. To handle this, a new sampled-data disturbance rejection control method is developed via a well-designed discrete-time dynamic event-triggered mechanism (DETM). First, a predictor-based generalized proportional integral observer is introduced to estimate the lumped disturbances, when only the sampled-data output is available. Then, a composite proportional feedback controller is formed by fully utilizing disturbance estimation. The composite controller updates only when the designed discrete-time DETM is violated, resulting in remarkable communication and computation resource savings while maintaining the desirable disturbance rejection ability. The designed DETM can be applied to digital computers easily due to the discrete-time detection. Simulations and experiments are carried out to validate the feasibility and effectiveness of the proposed control scheme.</p

Counteranion-Controlled Ag₂O‑Mediated Benzimidazolium Ring Opening and Its Application in the Synthesis of Palladium Pincer-Type Complexes

We report a new approach to synthesize palladium complexes through Ag₂O-promoted hydrolytic ring opening followed by palladium coordination. The novelty of Ag₂O-promoted hydrolysis in comparison with the commonly used base-mediated hydrolysis lies in the anion-controlled product selectivity in the synthesis of pincer-type palladium complexes. Moreover, these palladium complexes have been tested in the Suzuki reaction using aryl bromides in methanol and H₂O, respectively. In comparison with palladium complexes with normal coordination, the palladium complexes generated from the hydrolytic ring-opening coordination demonstrate excellent catalytic activity

Synthesis of α-arylalkylferrocenes through cesium fluoride-promoted coupling of arylboronic acids with <i>N</i>-tosylhydrazones

<p>A cesium fluoride-promoted reductive coupling reaction of acylferrocene tosylhydrazones with arylboronic acids has been developed, producing highly substituted α-arylalkylferrocenes in moderate to excellent yields. The reaction employs anionic fluorine to facilitate the cleavage of C–B bond. The developed methodology demonstrates a wide substrate scope and high functional groups tolerance. Moreover, the α-arylalkylferrocenes compounds were also obtained on a multi-gram scale.</p

Substrate-Controlled Product Divergence: Silver-Catalyzed Reaction of Trifluoromethyl Ketones with Terminal Alkynes

A distinct dichotomy in product distribution was initially observed in the silver-catalyzed reaction of trifluoromethyl (CF₃) ketones with terminal alkynes having two different types of electronic natures. The domino reaction smoothly proceeded almost exclusively with high stereoselectivity with terminal alkynes containing ester groups, whereas alkynylation occurred in good yield when terminal alkynes containing aryl or alkyl groups were present. The results indicated that the electronic nature of terminal alkynes can act as a switch that enables either the domino reaction or alkynylation between terminal alkynes and CF₃ ketones

Reactivity Switch Enabled by Counterion: Highly Chemoselective Dimerization and Hydration of Terminal Alkynes

A counterion-controlled reactivity tuning in Pd-catalyzed highly chemoselective and regioselective dimerization and hydration of terminal alkynes is reported. The use of acetate as counterion favors the formation of an alkenyl alkynyl palladium intermediate which forms hitherto less reported 1,3-diaryl-substituted conjugated enynes after reductive elimination. Using chloride, which is a better leaving group, leads to anion exchange on the alkenylpalladium intermediate with hydroxide which after reductive elimination and tautomerization delivered the hydration products

Substrate-Controlled Product Divergence: Silver-Catalyzed Reaction of Trifluoromethyl Ketones with Terminal Alkynes

A distinct dichotomy in product distribution was initially observed in the silver-catalyzed reaction of trifluoromethyl (CF₃) ketones with terminal alkynes having two different types of electronic natures. The domino reaction smoothly proceeded almost exclusively with high stereoselectivity with terminal alkynes containing ester groups, whereas alkynylation occurred in good yield when terminal alkynes containing aryl or alkyl groups were present. The results indicated that the electronic nature of terminal alkynes can act as a switch that enables either the domino reaction or alkynylation between terminal alkynes and CF₃ ketones

Metal-free oxidation of secondary benzylic alcohols using aqueous TBHP

<p>We report a simple, yet efficient metal-free oxidation of secondary benzylic alcohols in the presence of t-butyl hydroperoxide (70% TBHP) with high yields of up to 98%. This type of reaction can be carried out using a wide variety of substrates, requires no other organic solvent, and proves to be tolerant toward a variety of different functional groups.</p