Dendrimers in Catalysis

Most of the chemical reactions used to produce the molecules and materials that our societies need—for example, in the petrochemical and pharmaceutical industries, the synthesis of plastics and other materials, and the production of foods and drinks—make use of catalysts. These speed up the rate at which atoms and molecules rearrange themselves into new forms, and provide a degree of control over the shape and form of those rearrangements. Catalysts let us drive a chemical reaction in a selected direction, in preference to others that could occur. In this way they turn chemistry from crude cookery into a rational and precise form of molecular engineering. And always we can draw inspiration, and sometimes borrow tricks, from the delicate and precise catalytic processes that occur in nature, where enzymes carry out processes in aqueous solution and at mild temperatures and pressures that often we struggle to achieve with far more extreme conditions—such as the fixation of atmospheric nitrogen into useful forms. It is often claimed that this particular catalytic process—the Haber–Bosch process for converting nitrogen into ammonia, discovered just over a century ago—has, by making possible the synthesis of artificial fertilizers, had a greater effect on humankind than any other single chemical innovation. It is what allows us to feed the world. Yet while nature performs this reaction using soluble molecules (enzymes) as catalysts, the Haber–Bosch process uses powdered iron (plus some additives). The reactions between nitrogen and hydrogen take place on the surface of iron particles: this is so-called heterogeneous catalysis, involving surface chemistry, rather than the homogeneous catalysis of enzyme reactions, in which the catalysts are soluble molecules. Both homogeneous and heterogeneous catalysis are essential to the chemical industries. National Science Review spoke with two of the foremost practitioners of the latter field—Nobel laureate Gerhard Ertl of the Fritz Haber Institute in Berlin, Germany, and Avelino Corma of the Institute of Chemical Technology (ITQ) at the Polytechnic University of Valencia, Spain—about the current status of research in catalysis and prospects for the future.

Chapter 6 - Homogeneous catalysis: Characterization and spectroscopy

Review: 65 refs.

Homogeneous transition-metal catalysts are usually discrete molecules and can be synthesized by ligand design in a defined and rational way. To improve performance of homogenous catalysts, modification of catalysts is usually carried out within a close proximity of a metal center (within a few angstroms). This is effective way to develop efficient catalysts for various reactions including C-C bond-forming reactions and asymmetric reactions. Inspired by these findings, we set out to expand catalytic environment to nanosize by modification of ligands. Here the recent progress in homogeneous transition-metal catalysts with nanosize ligands is overviewed. To expand a molecular size, dendritic frameworks including flexible or rigid moieties, sterically congested m-terphenyl and its higher dendritic framework were introduced onto N-heterocyclic carbene and phosphine ligands.

Homogeneous transition metal catalysis: from the water gas shift reaction to nuclear waste vitrification

Paramagnetic (open-shell) systems, including transition metal ions, radical intermediates and defect centres, are often involved in catalytic transformations. Despite the prevalence of such species in catalysis, there are relatively few studies devoted to their characterisation, compared to their diamagnetic counterparts. Electron Paramagnetic Resonance (EPR) is an ideal technique perfectly suited to characterise such reaction centres, providing valuable insights into the molecular and supramolecular structure, the electronic structure, the dynamics and even the concentration of the paramagnetic systems under investigation. Furthermore, as EPR is such a versatile technique, samples can be measured as liquids, solids (frozen solutions and powders) and single crystals, making it ideal for studies in heterogeneous, homogeneous and enzyme catalysis. Coupled with the higher resolving power of the pulsed, higher frequency and hyperfine techniques, unsurpassed detail on the structure of these catalytic centres can be obtained. In this Chapter, we provide an overview to demonstrate how advanced EPR methods can be successfully exploited in the study of open-shell paramagnetic reaction centres in heterogeneous, homogeneous and enzymatic catalysts, including heme-based enzymes for use in biocatalysts, polymerisation based catalysts, supported microporous heterogeneous catalytic centres to homogeneous metal complexes for small molecule actions.

Recent developments in the one‐step thermal and photochemical catalytic hydroxylation of benzene to phenol using various oxidants are described, focusing on the catalytic mechanisms. Hydroxylation of benzene with hydrogen peroxide is catalyzed by homogeneous metal complexes and heterogeneous metal oxides to produce phenol when high‐valent metal‐oxo complexes are reactive species The selective hydroxylation of benzene to phenol is achieved by using mesoporous silica‐alumina as the catalyst support, which prohibits further oxidation of phenol due to the strongly acidic sites. Photocatalytic oxidation of benzene with dioxygen and water is made possible by using organic photocatalysts via photoinduced electron transfer from benzene to the excited states of the photocatalysts, followed by the hydroxylation of the benzene radical cation with water to yield phenol selectively. The further oxidation of phenol is prohibited because of the fast back electron transfer from the one‐electron reduced species of the photocatalyst to the phenol radical cation, whereas back electron transfer from the one‐electron reduced species to the benzene radical cation is slowed down because of the large driving force of the back electron transfer, which is in the Marcus inverted region.

The metal‐catalyzed oligomerization and polymerization of alkenes by homogeneous metal complexes has not only provided extraordinary insights into the chain‐growth process, it has also become of increasing commercial importance in delivering products of greater purity or improved properties. Novel materials not accessible using conventional heterogeneous catalysts can now be synthesized. Metals are no longer constrained to certain functions (titanium for polymerization, nickel for oligomerization) but span the range of molecular weights and polymer structures. This review discusses the fundamentals of chain‐growth polymerization catalyzed by homogeneous complexes and new developments in the field.

Tailored acidic deep eutectic solvents: A multifunctional co-catalyst mediating homogeneous catalysis and heterogeneous separation of ethylene methoxycarbonylation

The top 100 most-cited publications on contrast-enhanced ultrasound: A bibliometric analysis

10.31635/ccschem.021.202101063

Boron, as a unique element nearest to carbon in the periodic table, has been predicted to form many distinctive two‐dimensional (2D) structures that significantly differ from other well‐studied 2D materials, owning to its exceptional ability to form strong covalent two‐center‐two‐electron bonds as well as stable electron‐deficient multi‐center‐two‐electron bonds. Until recently, the successful syntheses of atomically thin crystalline 2D boron sheets (i.e., borophenes) provoked growing passion in 2D boron crystals. In this feature article, we present a survey of the latest achievements on 2D boron structures, starting from a concise introduction of the structures and properties of the bulk allotropes of boron, boron clusters, and especially potential building blocks for 2D boron crystals. Then we review important achievements and the current status of research on single‐layered metallic borophene, and discuss 2D few‐layered boron sheets, from their possible structures to tunable properties and potential applications in electronics, spintronics, and photoelectronics. We also systematically investigate the stability and functionalization of 2D icosahedral boron sheets in comparison with borophenes through first‐principles studies. Finally, we present an outlook on the advance in fabrications of 2D boron sheets, and the challenges and prospects in the realm of 2D boron crystals.

Core and periphery functionalized dendrimers for transition metal catalysis; a covalent and a non-covalent approach

Recent advancement in deoxygenation of fatty acids via homogeneous catalysis for biofuel production

Metabolic disorders such as diabetes and obesity are major public health concerns that affect millions of people worldwide. Epigenetic modifications have been implicated in the development and progression of these disorders, making them attractive targets for therapeutic intervention. The emergence of Clustered Regularly-Interspaced Short Palindromic Repeats (CRISPRCas-based) epigenome editing technology has revolutionized the field of gene editing and holds great promise for the treatment of metabolic disorders. However, there are still significant challenges and ethical concerns that must be addressed before this technology can be safely and effectively used in clinical applications. This review provides an overview of epigenetic modifications and their role in metabolic disorders, as well as an explanation of CRISPR-Cas-based epigenome editing and its potential applications. The current state of research and major findings on using this technology for the treatment of metabolic disorders are discussed, along with the advantages and limitations of different delivery strategies. The potential for off-target effects and unintended consequences, as well as strategies for minimizing or mitigating these effects, are also considered. Ethical and regulatory issues associated with CRISPR-Cas-based epigenome editing for metabolic disorders are discussed, with a focus on the importance of responsible development and implementation of this technology. The potential societal impacts of CRISPR-Cas-based epigenome editing for metabolic disorders are also considered. In conclusion, this review highlights the potential of CRISPR-Cas-based epigenome editing as a therapeutic strategy for metabolic disorders, but also underscores the importance of rigorous safety and efficacy testing and responsible implementation. Ultimately, the success of this technology will depend on a balanced consideration of the scientific, ethical, and societal implications.