Potential Utilization of Metal–Organic Frameworks in Heterogeneous Catalysis: A Case Study of Hydrogen‐Bond Donating and Single‐Site Catalysis

Crystalline solid materials are platforms for the development of effective catalysts and have shown vast benefits at the frontiers between homogeneous and heterogeneous catalysts. Typically, these crystalline solid catalysts outperformed their homogeneous analogs due to their high stability, selectivity, better catalytic activity, reusability and recyclability in catalysis applications. This point of view, comprising significant features of a new class of porous crystalline materials termed as metal‐organic frameworks (MOFs) engendered the attractive pathway to synthesize functionalized heterogeneous MOF catalysts. The present review includes the recent research progress in developing both hydrogen‐bond donating (HBD) MOF catalysts and MOF‐supported single‐site catalysts (MSSCs). The first part deals with the novel designs of urea‐, thiourea‐ and squaramide‐containing MOF catalysts and study of their crucial role in HBD catalysis. In the second part, we discuss the important classification of MSSCs with existing examples and their use in desired catalytic reactions. In addition, we describe the relative catalytic efficiency of these MSSCs with their homogeneous and similarly reported analogs. The precise knowledge of discussed heterogeneous MOF catalysts in this review may open the door for new research advances in the field of MOF catalysis.     

Iron‐Catalyzed Cross‐Couplings in the Synthesis of Pharmaceuticals: In Pursuit of Sustainability

The scarcity of precious metals has led to the development of sustainable strategies for metal‐catalyzed cross‐coupling reactions. The establishment of new catalytic methods using iron is attractive owing to the low cost, abundance, ready availability, and very low toxicity of iron. In the last few years, sustainable methods for iron‐catalyzed cross‐couplings have entered the critical area of pharmaceutical research. Most notably, iron is one of the very few metals that have been successfully field‐tested as highly effective base‐metal catalysts in practical, kilogram‐scale industrial cross‐couplings. In this Minireview, we critically discuss the strategic benefits of using iron catalysts as green and sustainable alternatives to precious metals in cross‐coupling applications for the synthesis of pharmaceuticals. The Minireview provides an essential introduction to the fundamental aspects of practical iron catalysis, highlights areas for improvement, and identifies new fields to be explored.     

DNA‐Based Hybrid Catalysts for Asymmetric Organic Synthesis

Stereoselective hybrid systems based on metal‐assisted catalysis with a chiral biomacromolecule form an attractive research area for the synthesis of enantiomerically pure compounds. Although various methods are available for this purpose, most rely on the use of enzymes, proteins, or RNA. The application of DNA‐based hybrid catalysts for enantioselective synthesis emerged only a few years ago. DNA‐based hybrid catalysts have been self‐assembled from DNA and a metal complex with a specific ligand through supramolecular or covalent anchoring strategies and have demonstrated high stereoselectivity and rate enhancement in Lewis acid catalyzed reactions, such as Diels–Alder, Michael addition, and Friedel–Crafts reactions. For these reactions, cheap and commercially available salmon testes DNA has generally been used. In this Minireview, we summarize recent developments in the area of asymmetric catalysis with DNA‐based hybrid catalysts.     

Synergistic Pd/Cu Catalysis in Organic Synthesis

Synergistic Pd/Cu catalysis has been utilized in the Sonogashira reaction since 1975. However, this strategy has not received much attention from the organic chemist community until recently. Synergistic Pd/Cu catalysis is becoming a proficient method for the development of catalytic reactions, including several new and efficient cross-coupling reactions. Additionally, several challenging asymmetric reactions, including stereodivergent synthesis, have been discovered by the combined use of a chiral metal catalyst and a second achiral metal catalyst or two chiral metal catalysts. This review provides an overview of this field, with the aims of highlighting both the development of synergistic Pd/Cu catalysis in organic synthesis and the reaction mechanisms involved in this research area.     

Laboratory Evolution of Stereoselective Enzymes: A Prolific Source of Catalysts for Asymmetric Reactions

Asymmetric catalysis plays a key role in modern synthetic organic chemistry, with synthetic catalysts and enzymes being the two available options. During the latter part of the last century the use of enzymes in organic chemistry and biotechnology experienced a period of rapid growth. However, these biocatalysts have traditionally suffered from several limitations, including in many cases limited substrate scope, poor enantioselectivity, insufficient stability, and sometimes product inhibition. During the last 15 years, the genetic technique of directed evolution has been developed to such an extent that all of these long‐standing problems can be addressed and solved. It is based on repeated cycles of gene mutagenesis, expression, and screening (or selection). This Review focuses on the directed evolution of enantioselective enzymes, which constitutes a fundamentally new approach to asymmetric catalysis. Emphasis is placed on the development of methods to make laboratory evolution faster and more efficient, thus providing chemists and biotechnologists with a rich and non‐ending source of robust and selective catalysts for a variety of useful applications.     

Selectivity Effects in Bimetallic Catalysis

An emerging area of homogeneous catalysis is the use of catalysts featuring two closely associated metal sites. This approach complements the traditional focus on single‐site catalysts and makes available new parameters with which to optimize catalytic behavior. Single‐site catalysts are optimized through changing 1) the identity of the metal, and 2) the steric and electronic properties of the ligands. Bimetallic catalysts introduce new optimization parameters such as 3) catalyst nuclearity (mononuclear vs. binuclear), and 4) bimetallic pairing (relative compatibility of two metal sites). In order to harness these new optimization parameters in developing systems, it is necessary to first understand the origin of bimetallic selectivity effects that already have been documented. This Concept article highlights bimetallic effects on the chemo‐, regio‐, and stereoselectivity of catalytic transformations, using selected case studies from the recent literature as illustrative examples.     

纳米碳材料非金属催化的研究进展

纳米碳材料直接作为催化剂的非金属碳催化是目前材料科学与催化领域的前沿方向之一.相对于传统金属催化剂,纳米碳材料催化剂具有高效环保、低能耗、耐腐蚀等优点.在烃类转化、化学品合成、能源催化等领域表现出优异的催化性能和发展潜力.综述了近年来纳米碳非金属催化研究的最新进展,主要包括新型纳米碳材料的表面性质、催化特性、反应机理和宏观制备等关键问题,并对纳米碳催化存在的挑战和前景进行了展望.     

Functionalized Silicas for Metal‐Free and Metal‐Based Catalytic Applications: A Review in Perspective of Green Chemistry

Heterogeneous catalysis plays a key role in promoting green chemistry through many routes. The functionalizable reactive silanols highlight silica as a beguiling support for the preparation of heterogeneous catalysts. Metal active sites anchored on functionalized silica (FS) usually demonstrate the better dispersion and stability due to their firm chemical interaction with FSs. Having certain functional groups in structure, FSs can act as the useful catalysts for few organic reactions even without the need of metal active sites which are termed as the covetous reusable organocatalysts. Magnetic FSs have laid the platform where the effortless recovery of catalysts is realized just using an external magnet, resulting in the simplified reaction procedure. Using FSs of multiple functional groups, we can envisage the shortened reaction pathway and, reduced chemical uses and chemical wastes. Unstable bio‐molecules like enzymes have been stabilized when they get chemically anchored on FSs. The resultant solid bio‐catalysts exhibited very good reusability in many catalytic reactions. Getting provoked from the green chemistry aspects and benefits of FS‐based catalysts, we confer the recent literature and progress focusing on the significance of FSs in heterogeneous catalysis. This review covers the preparative methods, types and catalytic applications of FSs. A special emphasis is given to the metal‐free FS catalysts, multiple FS‐based catalysts and magnetic FSs. Through this review, we presume that the contribution of FSs to green chemistry can be well understood. The future perspective of FSs and the improvements still required for implementing FS‐based catalysts in practical applications have been narrated at the end of this review.     

Metal‐Free Boron‐Containing Heterogeneous Catalysts

Metal‐free catalysts have distinct advantages over metal and metal oxide catalysts, such as lower cost as well as higher reliability and sustainability. Among the nonmetal compounds used in catalysis, boron‐containing compounds with a few unique properties have been developed. In this Minireview, the recent advances in the field of boron‐containing metal‐free catalysts are presented, including binary and ternary boron‐containing catalytic materials. Additionally, the three main applications in catalysis are considered, namely, electrocatalysis, thermal catalysis, and photocatalysis, with the role of boron discussed in depth for each specific catalytic application. Boron‐containing compounds could have a substantial impact on the field of metal‐free catalysts in the future.     

Colloids for Catalysts: A Concept for the Preparation of Superior Catalysts of Industrial Relevance

Compared to conventional preparation methods for supported heterogeneous catalysts, the use of colloidal nanoparticles (NPs) allows for a precise control over size, size distribution, and distribution/location of the NPs on the support. However, common colloidal syntheses have restrictions that limit their applicability for industrial catalyst preparation. We present a simple, surfactant‐free, and scalable preparation method for colloidal NPs to overcome these restrictions. We demonstrate how precious‐metal NPs are prepared in alkaline methanol, how the particle size can be tuned, and how supported catalysts are obtained. The potential of these colloids in the preparation of improved catalysts is demonstrated by two examples from heterogeneous catalysis and electrocatalysis.     

Platinum Group Organometallics Based on “Pincer” Complexes: Sensors,Switches, and Catalysts

Since the first reports in the late 1970s on transition metal complexes containing pincer‐type ligands—named after the particular coordination mode of these ligands—these systems have attracted increasing interest owing to the unusual properties of the metal centers imparted by the pincer ligand. Typically, such a ligand comprises an anionic aryl ring which is ortho,ortho‐disubstituted with heteroatom substituents, for example, CH₂NR₂, CH₂PR₂ or CH₂SR, which generally coordinate to the metal center, and therefore support the M−C σ bond. This commonly results in a terdentate and meridional coordination mode consisting of two metallacycles which share the M−C bond. Detailed studies of the formation and the properties of a large variety of pincers containing platinum group metal complexes have provided direct access to both a fundamental understanding of a variety of reactions in organometallic chemistry and to a range of new applications of these complexes. The discovery of alkane dehydrogenation catalysts, the mechanistic elucidation of fundamental transformations (for example, C−C bond activation), the construction of the first metallodendrimers for sustainable homogeneous catalysis, and the engineering of crystalline switches for materials processing represent only a few of the many highlights which have emanated from these numerous investigations. This review discusses the synthetic methodologies that are currently available for the preparation of platinum group metal complexes containing pincer ligands and especially emphasizes different applications that have been realized in materials science such as the development and engineering of sensors, switches, and catalysts.     

精确可控串联策略触发高效的氧还原活性

探索高效、经济的非金属氧还原(ORR)电催化剂已成为电化学能源体系的关键.科学界最具挑战性的目标之一是通过合理地验证和精确地调节活性位点来设计结构明确、性能优异的催化剂材料.本文提出一种精确和可控的串联协同作用的活性位点策略,以提高MFCOFs的ORR催化活性.以亚胺-N、噻吩-S和三嗪-N等作为结构单元,通过精确的串...     

Single-Site Heterogeneous Catalysts: From Synthesis to NMR Signal Enhancement

Catalysts with well-defined, single, active centers are of great importance and their utilization allows the gap between homo- and heterogeneous catalysis to be bridged and, importantly, the main selectivity problem of heterogeneous catalysis and the main separation challenge of homogeneous catalysis to be overcome. Moreover, the use of single-site catalysts allows the NMR signal to be significantly enhanced through the pairwise addition of two hydrogen atoms from a parahydrogen molecule to an unsaturated substrate. This review covers the fundamentals of the synthesis of single-site catalysts and shows the new aspects of their applications in both modern catalysis and the field of parahydrogen-based hyperpolarization. The different novel aspects of the formation and utilization of single-site catalysts, along with the possibility of NMR signal enhancement observations are described.     

Nanocarbons for Catalytic Desulfurization

Nanocarbon catalysts are green and sustainable alternatives to metal‐based catalysts for numerous catalytic transformations. The application of nanocarbons for environmental catalysis is an emerging research discipline and has undergone rapid development in recent years. In this focus review, we provide a critical analysis of state‐of‐the‐art nanocarbon catalysts for three different catalytic desulfurization processes. In particular, we focus on the advantages and limitations as well as the reaction mechanisms of the nanocarbon catalysts at the molecular level.     

Iridium‐ and Osmium‐decorated Reduced Graphenes as Promising Catalysts for Hydrogen Evolution

Renewable energy sources are highly sought after as a result of numerous worldwide problems concerning the environment and the shortage of energy. Currently, the focus in the field is on the development of catalysts that are able to provide water splitting catalysis and energy storage for the hydrogen evolution reaction (HER). While platinum is an excellent material for HER catalysis, it is costly and rare. In this work, we investigated the electrocatalytic abilities of various graphene–metal hybrids to replace platinum for the HER. The graphene materials were doped with 4f metals, namely, iridium, osmium, platinum and rhenium, as well as 3d metals, namely, cobalt, iron and manganese. We discovered that a few hybrids, in particular iridium‐ and osmium‐doped graphenes, have the potential to become competent electrocatalysts owing to their low costs and—more importantly—to their promising electrochemical performances towards the HER. One of the more noteworthy observations of this work is the superiority of these two hybrids over MoS₂, a well‐known electrocatalyst for the HER.     

Catalytic Enantioselective Flow Processes with Solid‐Supported Chiral Catalysts

Sustainability concerns are the wind in the sails for the development of novel, more selective catalytic processes. Hence, chiral catalysts play a crucial role in the green production of enantioenriched compounds. To further increase the green profile of this approach, the use of solid‐supported catalytic species is appealing due to the reduced generation of waste, as well as the possibility of reusing the precious catalyst. Even more attractive is the implementation of flow processes based on these immobilized catalysts, a flexible strategy that allows to generate from milli‐ to multi‐gram amounts of chiral product with a reduced footprint set‐up. Herein, we will present the efforts devoted in our laboratory towards the immobilization of chiral catalysts and their use in single‐pass, highly enantioselective, flow processes. Proline, diarylprolinols, other aminocatalysts, squaramides, thioureas, phosphoric acids and even chiral ligands and metal‐based catalysts constitute our current toolkit of supported species for enantioselective catalysis.     

Designed Precursor for the Controlled Synthesis of Highly Active Atomic and Sub‐nanometric Platinum Catalysts on Mesoporous Silica

The development of new methods to synthesize nanometric metal catalysts has always been an important and prerequisite step in advanced catalysis. Herein, we design a stable nitrogen ligated Pt complex for the straightforward synthesis by carbonization of uniformly sized atomic and sub‐nanometric Pt catalysts supported on mesoporous silica. During the carbonization of the Pt precursor into active Pt species, the nitrogen‐containing ligand directed the decomposition in a controlled fashion to maintain uniform sizes of the Pt species. The nitrogen ligand had a key role to stabilize the single Pt atoms on a weak anchoring support like silica. The Pt catalysts exhibited remarkable activities in the hydrogenation of common organic functional groups with turnover frequencies higher than in previous studies. By a simple post‐synthetic treatment, we could selectively remove the Pt nanoparticles to obtain a mixture of single atoms and nanoclusters, extending the applicability of the present method.     

钙钛矿材料在环境催化领域的应用现状及进展

日益严重的环境问题和有限的资源促使人们积极探索提高污染物处理效率,多相催化剂在环境污染高效治理中扮演着重要的角色,因此,高活性和高稳定性新型多相催化剂的开发成为一项非常有吸引力和具有挑战性的任务。钙钛矿材料因其高催化活性和稳定的晶体结构成为环境催化领域的研究热点。本文综述了钙钛矿材料特性、制备方法、新型钙钛矿材料发展现状和在环境催化领域的应用现状,并对其面临的挑战及未来发展方向进行了讨论。     

N‐Heterocyclic Carbenes: A New Concept in Organometallic Catalysis

N‐Heterocyclic carbenes have become universal ligands in organometallic and inorganic coordination chemistry. They not only bind to any transition metal, be it in low or high oxidation states, but also to main group elements such as beryllium, sulfur, and iodine. Because of their specific coordination chemistry, N‐heterocyclic carbenes both stabilize and activate metal centers in quite different key catalytic steps of organic syntheses, for example, C−H activation, C−C, C−H, C−O, and C−N bond formation. There is now ample evidence that in the new generation of organometallic catalysts the established ligand class of organophosphanes will be supplemented and, in part, replaced by N‐heterocyclic carbenes. Over the past few years, this chemistry has been the field of vivid scientific competition, and yielded previously unexpected successes in key areas of homogeneous catalysis. From the work in numerous academic laboratories and in industry, a revolutionary turning point in oraganometallic catalysis is emerging.     

New Generation of Biocatalysts for Organic Synthesis

The use of enzymes as catalysts for the preparation of novel compounds has received steadily increasing attention over the past few years. High demands are placed on the identification of new biocatalysts for organic synthesis. The catalysis of more ambitious reactions reflects the high expectations of this field of research. Enzymes play an increasingly important role as biocatalysts in the synthesis of key intermediates for the pharmaceutical and chemical industry, and new enzymatic technologies and processes have been established. Enzymes are an important part of the spectrum of catalysts available for synthetic chemistry. The advantages and applications of the most recent and attractive biocatalysts—reductases, transaminases, ammonia lyases, epoxide hydrolases, and dehalogenases—will be discussed herein and exemplified by the syntheses of interesting compounds.