Catalytic System Research Articles

Modulating the Aggregation States of a Pd6L4 Cage for Selectivity Flipping during the Stereo‐Divergent Semi‐Hydrogenation of Alkynes

An enzyme‐mimicking catalytic system has been established using a singular palladium‐based octahedral cage as the supramolecular reactor, deftly unlocking off‐on‐off selectivity in the semi‐hydrogenation of alkynes. Water serves as a critical regulator, modulating the catalyst states, reaction rates, and endpoints. The choice of solvent system influences the activity of host‐guest binding and the reaction types of homogeneous and heterogeneous catalysis, effectively modifying the reaction steps involved in the Z→E isomerization during the semi‐hydrogenation of alkynes. Kinetic and inhibition experiments indicate that the catalyst mimics the binding and activation characteristics of enzymes towards substrates, enabling selective transformations within the confined enzyme‐mimicking environment. The utility of this switchable cage‐confined catalysis has been demonstrated in the synthesis and modification of complex biologically active molecules with controllable E/Z selectivity. This work sheds light on the design and control of artificial supramolecular counterparts of enzymes, offering fundamental insights into the factors influencing the activity and catalytic selectivity of biological macromolecules.

Vertically Expanded Covalent Organic Frameworks for Photocatalytic Water Oxidation into Oxygen

Covalent organic frameworks with unique π architectures and pores could be developed as photocatalysts for transformations. However, they usually form π‐stacking layers, so that only surface layers function in photocatalysis. Here we report a strategy for developing vertically expanded frameworks to expose originally inaccessible active sites hidden in layers to catalysis. We designed covalently linked two‐dimensional cobalt(II) porphyrin layers and explored coordination bonds to connect the cobalt(II) porphyrin layers with bidentate ligands via a three‐component one‐pot polymerization. The frameworks expand the interlayer space greatly, where both the up and down faces of each cobalt(II) porphyrin layer are exposed to reactants. Unexpectedly, the vertically expanded frameworks increase skeleton oxidation potentials, decrease exciton dissociation energy, improve pore hydrophilicity and affinity to water, and facilitate water delivery. Remarkably, these positive effects work collectively in the photocatalysis of water oxidation into oxygen, with an oxygen production rate of 1155 µmol g−1 h−1, a quantum efficiency of 1.24% at 450 nm, and a turnover frequency of 1.39 h−1, which is even 5.1‐fold as high as that of the π‐stacked frameworks and ranks them the most effective photocatalysts. This strategy offers a new platform for designing layer frameworks to build various catalytic systems for chemical transformations.

Vertically Expanded Covalent Organic Frameworks for Photocatalytic Water Oxidation into Oxygen.

Covalent organic frameworks with unique π architectures and pores could be developed as photocatalysts for transformations. However, they usually form π-stacking layers, so that only surface layers function in photocatalysis. Here we report a strategy for developing vertically expanded frameworks to expose originally inaccessible active sites hidden in layers to catalysis. We designed covalently linked two-dimensional cobalt(II) porphyrin layers and explored coordination bonds to connect the cobalt(II) porphyrin layers with bidentate ligands via a three-component one-pot polymerization. The frameworks expand the interlayer space greatly, where both the up and down faces of each cobalt(II) porphyrin layer are exposed to reactants. Unexpectedly, the vertically expanded frameworks increase skeleton oxidation potentials, decrease exciton dissociation energy, improve pore hydrophilicity and affinity to water, and facilitate water delivery. Remarkably, these positive effects work collectively in the photocatalysis of water oxidation into oxygen, with an oxygen production rate of 1155 µmol g-1 h-1, a quantum efficiency of 1.24% at 450 nm, and a turnover frequency of 1.39 h-1, which is even 5.1-fold as high as that of the π-stacked frameworks and ranks them the most effective photocatalysts. This strategy offers a new platform for designing layer frameworks to build various catalytic systems for chemical transformations.

Modulating the Aggregation States of a Pd6L4 Cage for Selectivity Flipping during the Stereo-Divergent Semi-Hydrogenation of Alkynes.

An enzyme-mimicking catalytic system has been established using a singular palladium-based octahedral cage as the supramolecular reactor, deftly unlocking off-on-off selectivity in the semi-hydrogenation of alkynes. Water serves as a critical regulator, modulating the catalyst states, reaction rates, and endpoints. The choice of solvent system influences the activity of host-guest binding and the reaction types of homogeneous and heterogeneous catalysis, effectively modifying the reaction steps involved in the Z→E isomerization during the semi-hydrogenation of alkynes. Kinetic and inhibition experiments indicate that the catalyst mimics the binding and activation characteristics of enzymes towards substrates, enabling selective transformations within the confined enzyme-mimicking environment. The utility of this switchable cage-confined catalysis has been demonstrated in the synthesis and modification of complex biologically active molecules with controllable E/Z selectivity. This work sheds light on the design and control of artificial supramolecular counterparts of enzymes, offering fundamental insights into the factors influencing the activity and catalytic selectivity of biological macromolecules.

C‐C Coupling of Methylene Ketones with Alcohols Enabled by Fe‐Catalysis: Access to Substituted Pyrroles and Pharmaceuticals

Herein, we have reported a sustainable and chemo‐selective strategy for the synthesis of functionalized branched alcohols. Commercially available catalytic system does not need any special ligand and liberated water and hydrogen as side product. A series of alkyl primary alcohols (C4‐C10) including methanol were tolerated in good to high yield. Sequential transformations to substituted pyrroles, chromenes and synthesis of donepezil drug were obtained (>57 entries). Preliminary mechanistic investigations were performed to understand the catalytic pathways.

Regio‐ and Diastereoselective One‐pot Double Cascade Hybrid Formation/[3+3] Spirocyclization for the Synthesis of 3‐Spiropiperidines Under Phase Transfer Conditions.

Herein, we report an efficient approach to synthesizing hybrid 3‐spiropiperidines heterocycles that incorporate both 3‐isochromanone and 3‐isoindolinone units through a one‐pot, double cascade reaction facilitated by an economical K₂CO₃/TBAB catalytic system. By examining the nucleophilicity of the lactone 3‐isochromanone, we developed a cascade reaction pathway that first generates a bi‐nucleophilic hybrid intermediate, which then undergoes [3+3] spirocyclization with α,β‐unsaturated aldehydes. The regioselectivity of the spirocyclization strongly depends on the substitution pattern of lactam ring. The process exhibits high diastereoselectivity, even with the formation of three or four stereocenters, including two contiguous quaternary carbons. These sequential cascade reactions were successfully scaled up, and the subsequent reactivity was readily analyzed, enabling the transformation of existing functional groups into valuable new functionalities.

Modulating N−H Bond Cleavage in Catalytic Ammonia Oxidation Reaction

AbstractThe ammonia oxidation reaction (AOR) exhibits significant potential for environmental remediation and energy utilization. Nevertheless, the complex reaction mechanism of the AOR poses numerous challenges to its application. To overcome these challenges and realize an efficient AOR process, a thorough understanding of every elementary reaction step, especially the cleavage of N−H bonds, is crucial. This review delves into the influence of N−H bond cleavage on the rate and selectivity of AOR, and summarizes the latest advancements in promoting this crucial step. Furthermore, we discuss the challenges faced by N−H bond cleavage and provide insights into the design of efficient catalytic AOR systems.

Zinc bioinspired catalytic system for the valorisation of CO2 into cyclic carbonates

Cyclic organic carbonates are defined as key compounds for a sustainable chemical economy. Their synthesis from CO2 under mild conditions is a useful way to valorise this greenhouse gas as carbon source. Even if a wide range of catalysts were described to promote the carbon dioxide cycloaddition into epoxides, only few ones concern enzymatic systems. The zinc/L‐histidine active site of carbonic anhydrase inspired the present work, pointing out that the imidazole moiety of the amino acid ligand has a crucial role. An extensive study was undertaken to establish the structure‐activity relationship of imidazole derivatives, zinc salts and their respective catalytic activity in the CO2 cycloaddition reaction. The effect of aromatic, alkyl or iodine substituents and their position in N‐heterocycles were highlighted. A synergic effect was noted when combining imidazole compounds with zinc salts. The optimisation of reaction conditions emphasised the in‐situ ZnI2/1‐methylimidazole catalytic system is selective towards cyclic styrene carbonates and efficient under solvent‐free mild conditions (50°C, atmospheric CO2 pressure). Once reusing tests confirmed the catalytic system robustness, the reaction scope was enlarged to several epoxides resulting in 84‐99% yields of their corresponding cyclic carbonates.

Pd/Mengphos-Catalyzed High-Order [4+4] Cycloaddition for Efficient Synthesis of Oxazocines

AbstractThe development of new catalytic systems that enable regio- and chemoselective construction of diversely functionalized oxazocines is an important topic in organic synthesis and pharmacochemistry. Herein, a novel Pd/Mengphos complex was designed and applied in a palladium-catalyzed high-order [4+4] cycloaddition of 2-substituted allylic carbonates to α,β-unsaturated imines, allowing facile access to versatile oxazocines in good yields with excellent b/l and Z/E selectivities (up to 92% yield and complete b/l and Z/E selectivities). The reaction exhibited a broad substrate scope, mild reaction conditions, and good functional group compatibility. In addition, an asymmetric version has also been tested, affording the desired oxazocines in moderate to good enantioselectivity.

Synthesis of Functionalized Cycloheptadienones Starting from Phenols and Using a Rhodium/Boron Asymmetric Catalytic System

Skeletal editing offers a unique route to assemble complex architectures from simple feedstocks that are otherwise difficult to obtain. However, the asymmetric version of skeletal editing has not been widely studied. Herein, we present a modular rhodium/boron asymmetric catalytic system that enables ring‐expansion of phenols with cyclopropenes to synthesize highly functionalized cycloheptadienones in excellent chemo‐ and regioselectivities. This unique protocol features with low‐catalyst loading, atom and step‐economies, and mild neutral reaction conditions. Isotope‐labelling experiments and DFT calculations have been conducted to reveal that boron reagent plays a vital role in the whole catalytic cycle.

Synthesis of Functionalized Cycloheptadienones Starting from Phenols and Using a Rhodium/Boron Asymmetric Catalytic System.

Skeletal editing offers a unique route to assemble complex architectures from simple feedstocks that are otherwise difficult to obtain. However, the asymmetric version of skeletal editing has not been widely studied. Herein, we present a modular rhodium/boron asymmetric catalytic system that enables ring-expansion of phenols with cyclopropenes to synthesize highly functionalized cycloheptadienones in excellent chemo- and regioselectivities. This unique protocol features with low-catalyst loading, atom and step-economies, and mild neutral reaction conditions. Isotope-labelling experiments and DFT calculations have been conducted to reveal that boron reagent plays a vital role in the whole catalytic cycle.

Design of a New Catalyst, Manganese(III) Complex, for the Oxidative Degradation of Azo Dye Molecules in Water Using Hydrogen Peroxide

In the current work, chloro(meso-tetrakis(phenyl)porphyrin) manganese(III) [Mn(TPP)Cl] was synthesized following two steps: the preparation of meso-tetraphenylporphyrin (H⁠2TPP) and the insertion of manganese into the free porphyrin H2TPP. The compounds were characterized using SEM, FT-IR, UV, TGA/DTA, and XRD analyses. Manganese(III) meso-porphyrins exhibited hyper-type electronic spectra with a half-vacant metal orbital with symmetry, such as [dπ:dxz and dyz]. The thermal behavior of [Mn(TPP)(Cl)] changed (three-step degradation process) compared to the initial H2TPP (one-step degradation process), confirming the insertion of manganese into the core of the free porphyrin H2TPP. Furthermore, [Mn(TPP)Cl] was used to degrade calmagite (an azo dye) using H2O2 as an oxidant. The effects of dye concentration, reaction time, H2O2 dose, and temperature were investigated. The azo dye solution was completely degraded in the presence of [Mn(TPP)(Cl)]/H2O2 at pH = 6, temperature = 20 °C, C0 = 30 mg/L, and H2O2 = 40 mL/L. The computed low activation energy (Ea = 10.55 Kj/mol) demonstrated the efficiency of the proposed catalytic system for the azo dye degradation. Overall, based on the synthesis process and the excellent catalytic results, the prepared [Mn(TPP)Cl] could be used as an effective catalyst for the treatment of calmagite-contaminated effluents.

Dication Disulfuranes as Photoactivatable Sources of Radical Organocatalysts.

The recent development of photoredox and energy transfer catalysis has led to a significant expansion of visible light-driven chemical transformations. These methods have demonstrated exceptional efficiency in converting a wide range of substrates into radical intermediates and generating open-shell catalytic species. However, the simplification of catalytic systems and the direct generation of highly reactive radical organocatalysts through direct visible light irradiation from stable precatalysts remains largely an unrealized goal. This challenge is mainly due to the limited availability of precatalysts that are responsive to visible light. Herein, we introduce a new class of bench-stable dicationic disulfuranes, which release highly reactive thiyl radicals upon blue light excitation. Spectroscopic and computational studies reveal that this reactivity arises from a combination of structural features and intermolecular interactions. This family of molecules has been employed to catalyze radical cascades previously incompatible with photoredox conditions, enabling the efficient formation of 1,2-dioxolanes and 1,3-hydroxyketones in excellent yields and short reaction times.

Dication Disulfuranes as Photoactivatable Sources of Radical Organocatalysts

The recent development of photoredox and energy transfer catalysis has led to a significant expansion of visible light‐driven chemical transformations. These methods have demonstrated exceptional efficiency in converting a wide range of substrates into radical intermediates and generating open‐shell catalytic species. However, the simplification of catalytic systems and the direct generation of highly reactive radical organocatalysts through direct visible light irradiation from stable precatalysts remains largely an unrealized goal. This challenge is mainly due to the limited availability of precatalysts that are responsive to visible light. Herein, we introduce a new class of bench‐stable dicationic disulfuranes, which release highly reactive thiyl radicals upon blue light excitation. Spectroscopic and computational studies reveal that this reactivity arises from a combination of structural features and intermolecular interactions. This family of molecules has been employed to catalyze radical cascades previously incompatible with photoredox conditions, enabling the efficient formation of 1,2‐dioxolanes and 1,3‐hydroxyketones in excellent yields and short reaction times.

Direct Access to α,β‐Unsaturated γ‐Lactams via Palladium‐Catalysed Carbonylation of Propargylic Ureas

Abstract. Additive carbonylations typically necessitate strong nucleophiles, such as alcohols or amines. In this study, we carbonylated a poorly nucleophilic urea, under oxidant‐free conditions. Our straightforward carbonylative strategy enables access to versatile α,β‐unsaturated γ‐lactams featuring an aminocarbonyl fragment, utilizing readily available propargylic ureas as starting materials. The employment of the PdI2/KI catalytic system allowed complete regioselectivity (5‐endo‐dig), high functional group tolerance, broad substrate scope as well as operational simplicity (oxidant‐free, organic ligand‐free and base‐free protocol). The synthetic utility of these γ‐lactams is showcased through late‐stage functionalizations, such as Giese reactions and peptide couplings.

An Ambient Measurement Technique for Vehicle Emission Quantification and Concentration Source Apportionment.

We develop a new technique called plume regression where fast response instruments located at the roadside are used to measure exhaust plumes of passing vehicles. The approach is used to generate highly disaggregated vehicle emissions information by vehicle type, which compares well with traditional vehicle emission remote sensing. Additionally, the technique provides valuable new information on ambient concentration source apportionment by vehicle type. The technique is flexible enough to consider a wide range of air pollutants and be deployed at roadside ambient monitoring locations. The new approach is used to quantify emissions and concentration source apportionment for ammonia (NH3) and nitrogen oxides (NOx). We find that emissions of NH3 are generally very well controlled from diesel vehicles including those with selective catalytic reduction systems that use NH3 to reduce emissions of NOx. By contrast, gasoline passenger cars are shown to be the dominant contributor to NH3 emissions, which increase with vehicle mileage. Average fuel-specific NH3 emission factors for gasoline vehicles range from 0.3 to 1.2 g kg-1, while diesel vehicle emission factors remain below 0.06 g kg-1, with the exception of Euro VI buses with the latest regulatory provisions (0.5 g kg-1).

Green synthesis of benzimidazole derivatives using copper(II)-supported on alginate hydrogel beads

The study addresses the challenge of developing sustainable and efficient catalytic systems for the synthesis of benzimidazole derivatives, which are of significant importance in the field of medicinal chemistry due to their diverse biological activities. The objective is to develop a recyclable and environmentally friendly catalyst utilizing copper(II)-loaded alginate hydrogel beads, which can facilitate the synthesis of these compounds while minimizing environmental impact. The preparation process entails crosslinking sodium alginate with copper(II) ions to form hydrogel beads, which are then washed and characterized through techniques such as scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Inductively coupled plasma (ICP), and Zeta potential to analyses the morphology, composition and porosity of the beads. The catalytic performance is evaluated through recycling tests, which demonstrate the catalyst's ability to maintain selectivity and activity over multiple reaction cycles. The Cu(II)-Alg hydrogel beads were used for synthesizing substituted benzimidazole derivatives in a water-ethanol solvent at room temperature. This method offers significant advantages, including extremely mild reaction conditions, short reaction times (<1 h), high yields (70–94 %), and ease of processing. The most significant results indicate that the Cu(II)-alginate catalyst exhibits a high loading capacity and retains its catalytic efficiency for at least 3 cycles, thereby highlighting its potential for sustainable applications in organic synthesis.

Constructing Organic-Inorganic Woven Hybrid Membrane for Highly-Selective Catalytic Conversion of Lignin-based Phenolic Molecule to Value-added Products

Addressing the global need for sustainable chemical processes, this study introduces an innovative Woven Hybrid Membrane (WHM) specifically designed for the efficient oxidation of vanillyl alcohol (VAA) to vanillin (VLN). This transformation is crucial for converting lignocellulosic biomass into valuable chemical products, aligning with sustainable development goals. Utilizing a novel catalytic system that combines 2,2,6,6-tetramethylpiperidine 1-oxyl (TMP) and copper on a unique mesh-like structure, the WHM enhances both the economic and environmental viability of the process. This design not only overcomes the limitations of powdered catalysts, which are challenging to recover and reuse, but also promotes high catalytic efficiency and selectivity. By employing oxygen as the oxidant, our system maintains near 100% selectivity for VLN, demonstrating high conversion rates across multiple cycles without significant degradation in performance. Advanced analytical techniques, including electrochemical analysis and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), were used to explore the catalyst’s functionality and the reaction mechanism. The results confirm the stability and effectiveness of the WHM, showcasing its potential as a reusable, highly efficient, and environmentally friendly catalyst. This research represents a significant step forward in the field of sustainable industrial chemistry, offering a robust solution for the bio-refinery industry's push towards greener processes.

Dopant effects on the environment-dependent chemical properties of NiO(100) surfaces

NiO is a promising material for applications such as electronic devices and catalysts due to its low cost, environmental friendliness, and optimal chemical and electronic properties. Inclusion of a dopant element into the NiO near surface structure can further tune material properties. Despite extensive studies on doped NiO (M−NiO) materials, there remains a lack of knowledge regarding the connection between dopant, environment-dependent dominant near surface structures, and overall chemical properties. Here, the dopant effects on the near surface structure and electronic properties on M−NiO(100) are systematically examined using a combination of density functional theory (DFT) and ab initio phase diagrams. The simultaneous factors tested include dopant element (Al, Mo, Nb, Sn, Ti, V, W, or Zr), dopant placement (surface or subsurface), Ni/O vacancies (surface or subsurface), and oxygen species (O* or O2*) adsorption. The results reveal the dominant structures and compositions of M−NiO(100) under a wide range of environmental conditions (i.e. varying temperature and pressure). Subsequent electronic analyses of the dominant M−NiO(100) structures shows non-uniform changes in charge redistribution, band gap, work function, and d-band center with dopant and near surface structure, emphasizing the role of dopants in tuning M−NiO(100) both geometric and electronic properties. Overall, these multiscale modeling results enable a rapid, effective, and a priori prediction of dominant M−NiO(100) structures with distinct chemical properties, crucial for guiding NiO-based materials design with enhanced performance for advanced electronics, energy storage, and catalytic systems.

Electro-assisted carbon nanotube dual catalytic membrane system for high-efficiency and energy-efficient water treatment

Electro-assisted carbon nanotube dual catalytic membrane system for high-efficiency and energy-efficient water treatment