Covalent organic frameworks (COFs) are promising candidates as heterogeneous photocatalysts because of their porosity and tunable light absorption. The photostability and charge separation of COFs ...are highly important to improve the efficiency of photocatalytic transformation. In this work, a fully conjugated donor–acceptor COF is constructed with a benzothiadiazole unit, which exhibits high stability and enhanced charge separation. The prepared COF can efficaciously produce superoxide radical anions under air and visible light, which mediate the photocatalytic oxidative amine coupling and cyclization of thioamide to 1,2,4-thiadiazole in moderate to high yield and high recyclability (18 examples). This study demonstrates the great capacity of fully conjugated COFs with a D–A structure for light-driven organic synthesis.
In this work, the biofuel target compound 2-ethyl-5,5-dimethylcyclopenta-1,3-diene (1) and its exo isomers (9a and 9b), were successfully synthesized via two different pathways from the common ...intermediate 4,4-dimethylcyclopent-2-ene-1-one (2). The first pathway produced the endocyclic product as a pure isomer via a triflate intermediate obtained from the ketone 2 in 60% yield, followed by copper catalyzed coupling with ethyl magnesium bromide in 63% yield. The second pathway employed a Grignard reaction with ketone 2, which generated an alcohol that was immediately subjected to mild acid catalyzed elimination upon workup of the previous step to yield a primarily a mixture of exo diastereomers 9a and 9b in 77% yield. These targets had their fuel properties characterized in a separate study.
An unprecedented efficient protocol is developed for the oxidative cleavage of C≡C bonds in alkynes to produce structure-diverse esters using heterogeneous cobalt nanoparticles as catalyst with ...molecular oxygen as the oxidant. A diverse set of mono- and multisubstituted aromatic and aliphatic alkynes can be effectively cleaved and converted into the corresponding esters. Characterization analysis and control experiments indicate high surface area and pore volume, as well as nanostructured nitrogen-doped graphene-layer coated cobalt nanoparticles are possibly responsible for excellent catalytic activity. Mechanistic studies reveal that ketones derived from alkynes under oxidative conditions are formed as intermediates, which subsequently are converted to esters through a tandem sequential process. The catalyst can be recycled up to five times without significant loss of activity.
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•Esterification of alkynes via oxidative cleavage of C≡C bonds•Heterogeneous cobalt nanoparticles as catalyst and oxygen as oxidant•Excellent functional group compatibility, facile scalability, and a broad substrate scope•A significant advancement in developing heterogeneous catalyst for unsaturated hydrocarbons
Organic synthesis; Interface science
Carbon-based materials are widely employed as metal-free catalysts or supports in catalysis, energy, and ecological applications because of their interesting properties. Generally, their high surface ...areas, size, shape, porosity, and the possibility of incorporating additional moieties through chemical functional designs are believed to be essential for enriching the catalytic activity of carbon-containing materials. Lately, the new field of single-atom catalysts (SACs) has emerged as the finest alternative for not only homogeneous but also heterogeneous catalysts used in various kinds of catalytic applications. Among a variety of SACs, carbon-based SACs are widely investigated catalysts because of their extraordinary features such as tunable morphologies, ordered porosity, and effortless immobilization through various metals (noble and non-noble), making them highly efficient single-atom catalysts for numerous important catalytic applications. Herein, we intend to report on the progress achieved in researching carbon-based single-atom catalysts, including primarily metals such as Co, Cu, Zn, Pd, Ni, Pt, among others, embedded in carbon matrices and applied to applications in organic catalysis, photocatalysis, and electrocatalysis. It is important to point out that the main focus of this Review is directed to the activity and applications of single-atom catalysts, which are discussed in detail; thus, characterization and rationalization are excluded. Finally, we provide a future perspective on the development and progress made on a carbon-based single metal atom for catalysis.
Thiamine (VB1) has been proved to be a powerful biocatalyst for various organic transformations. VB1 offers several unique advantages, such as economical, non‐toxic, stable and water soluble. ...Excellent outcomes have been achieved in synthetic applications using VB1 as a catalyst. This review summarizes recent developments in the field of VB1 biocatalysis, allowing the construction of various biologically active heterocyclic scaffolds.
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•Molecular oxygen activation via energy and charge transfer processes is summarized.•Molecular oxygen activation pathway analysis and reactive oxygen detection methods are ...introduced.•Application of activated molecular oxygen in oxidation reactions is reviewed.
Molecular oxygen is the greenest potential oxidant, but its spin-forbidden nature limits its activation and application. The use of photocatalysis technology to activate molecular oxygen into reactive oxygen species (ROS) is a feasible strategy for initiating molecular oxygen activation performance from the activation methods of energy transfer process and charge transfer process, such as improving the efficiency of inter-system crossing, reducing non-radiative decay, and enhancing molecular oxygen adsorption and charge separation efficiency. New perspectives on the analysis of molecular oxygen activation pathways and the detection methods of ROS are introduced. In addition, the application of activated molecular oxygen in some oxidative reactions including degradation of organic pollutants, organic synthesis and photodynamic therapy of tumors are summarized. Finally, conclusions and challenges are briefly presented.
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•The use of chitosan an abundant, green material with important contribution to catalysis and sustainable chemistry.•Selection of a wide range of chitosan-based catalyst materials ...with varied metal species (ions, complexes, nanoparticles).•Chitosan-based metal catalysts applied in a broad range of chemical transformations.•Focus on structural characteristics and related catalyst performance.
Chitosan is an abundant, biodegradable, and renewable green material with diverse functionalities. It is a valuable substance used prolifically in numerous applications, such as catalysis, adsorption, delivery of therapeutic agents, and remediation. This review attempts to collect useful information with respect to the use of chitosan and modified chitosan preparations loaded with metal ions, complexes and metal particles as catalysts in organic transformations. These include coupling reactions, oxidations, hydrogenations and reductions, and multicomponent syntheses. Examples of miscellaneous other transformations and electrochemical reactions are also covered. A few chiral applications and results of recycling studies are also treated together with selected examples about the removal of toxic materials. Data collected and analyzed will indicate the importance and high potential of chitosan-based metal catalysts in sustainable chemistry.
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