Hydroformylation of Olefins by a Rhodium Single‐Atom Catalyst with Activity Comparable to RhCl(PPh3)3

Homogeneous catalysts generally possess superior catalytic performance compared to heterogeneous catalysts. However, the issue of catalyst separation and recycling severely limits their use in practical applications. Single‐atom catalysts have the advantages of both homogeneous catalysts, such as “isolated sites”, and heterogeneous catalysts, such as stability and reusability, and thus would be a promising alternative to traditional homogeneous catalysts. In the hydroformylation of olefins, single‐atom Rh catalysts supported on ZnO nanowires demonstrate similar efficiency (TON≈40000) compared to that of homogeneous Wilkinson's catalyst (TON≈19000). HAADF‐STEM and infrared CO chemisorption experiments identified isolated Rh atoms on the support. XPS and XANES spectra indicate that the electronic state of Rh is almost metallic. The catalysts are about one or two orders of magnitude more active than most reported heterogeneous catalysts and can be reused four times without an obvious decline in activity.     

Asymmetric hydrogenation using chiral Rh complexes immobilised with a new ion-exchange strategy

Rh diphosphine complexes using DuPhos and JosiPhos as chiral ligands have been immobilised by ion exchange into the mesoporous material MCM-41. When used as catalysts for the enantioselective hydrogenation of dimethyl itaconate and methyl-2-acetamidoacrylate, these heterogeneous catalysts give catalytic performance in terms of yield and enantioselection that are comparable to the corresponding homogeneous catalysts. Furthermore, the heterogeneous catalysts can be readily recovered and reused without loss of catalyst performance. A second immobilisation strategy is described in which [Rh(COD)2]+BF4- is initially immobilised by ion exchange and subsequently modified by the chiral diphosphine and this give comparable catalyst performance. This immobilisation strategy opens up the possibility of easy ligand-screening for parallel synthesis and libraries.     

Asymmetric Epoxidation of cis/trans‐β‐Methylstyrene Catalysed by Immobilised Mn(Salen) with Different Linkages: Heterogenisation of Homogeneous Asymmetric Catalysis

Immobilised Mn(salen) catalysts with two different linkages were studied in the asymmetric epoxidation of cis/trans‐β‐methylstyrene using NaClO as oxidant. The immobilised Mn(salen) complexes inside nanopores can lead to different catalytic behaviour compared with that of homogeneous Jacobsen catalyst. The rigidity of the linkage was found to be a key factor affecting the catalytic performance of immobilised catalysts. The immobilised catalyst with a rigid linkage exhibited comparable chemical selectivity, enantioselectivity and cis/trans ratio of product formation to that obtained with homogeneous Jacobsen catalysts. In contrast, the immobilised catalyst with a flexible linkage gave remarkably lower chemical selectivity, enantioselectivity and inverted cis/trans ratio compared with the results obtained with the homogeneous Jacobsen catalyst and the immobilised catalyst with rigid linkage. Thus, for immobilised Mn(salen) catalysts, a rigid linkage connecting active centres to the support is essential to obtain activity and enantioselectivity as high as those obtained in homogeneous systems.     

Selective Homogeneous and Heterogeneous Gold Catalysis with Alkynes and Alkenes: Similar Behavior,Different Origin

The development of new sustainable chemical processes requires the implementation of ultra‐selective reaction processes. The enormous selectivity found for gold‐based catalysts when applied in several reactions has opened new frontiers. For instance, the selective activation of alkynes is a common feature for both homogeneous and heterogeneous gold catalysts. Herein, we employ experimental and theoretical methods to assess the similarities and differences in the performance of homogeneous and heterogeneous gold catalysts. Alkynophilicity, the selective activation of alkynes, is found to have a thermodynamic origin in the heterogeneous case and a kinetic one for homogeneous catalysis. Complex enyne rearrangements require the more active homogeneous (single gold) catalyst because it has more electrophilic character than its heterogeneous (nanoparticle) counterpart.     

Metalloporphyrin‐Based Hypercrosslinked Polymers Catalyze Hetero‐Diels–Alder Reactions of Unactivated Aldehydes with Simple Dienes: A Fascinating Strategy for the Construction of Heterogeneous Catalysts

We describe a novel and intriguing strategy for the construction of efficient heterogeneous catalysts by hypercrosslinking catalyst molecules in a one‐pot Friedel–Crafts alkylation reaction. The new hypercrosslinked polymers (HCPs) as porous solid catalysts exhibit the combined advantages of homogeneous and heterogeneous catalysis, owing to their high surface area, good stability, and tailoring of catalytic centers on the frameworks. Indeed, a new class of metalloporphyrin‐based HCPs were successfully synthesized using modified iron(III) porphyrin complexes as building blocks, and the resulting networks were found to be excellent recyclable heterogeneous catalysts for the hetero‐Diels–Alder reaction of unactivated aldehydes with 1,3‐dienes. Moreover, this new strategy showed wide adaptability, and many kinds of homogeneous‐like solid‐based catalysts with high catalytic performance and excellent recyclability were also constructed.     

Homogeneous nanosize palladium catalysts

Expanding the catalytic environment to a nanosize must be one of the most promising ways to improve the performance of homogeneous catalysts. In this Forum Article, recent developments in homogeneous nanosize palladium catalysts are reviewed. It contains solubilized palladium nanoparticles, metalated dendrimers, and complexes with well-defined nanosized ligands. These systems realize efficient catalyst recycling, unique selectivity, suppression of metal aggregation, and remarkable enhancement of the catalytic activity.     

Ordered Porous Nitrogen‐Doped Carbon Matrix with Atomically Dispersed Cobalt Sites as an Efficient Catalyst for Dehydrogenation and Transfer Hydrogenation of N‐Heterocycles

Single‐atom catalysts (SACs) have been explored widely as potential substitutes for homogeneous catalysts. Isolated cobalt single‐atom sites were stabilized on an ordered porous nitrogen‐doped carbon matrix (ISAS‐Co/OPNC). ISAS‐Co/OPNC is a highly efficient catalyst for acceptorless dehydrogenation of N‐heterocycles to release H₂. ISAS‐Co/OPNC also exhibits excellent catalytic activity for the reverse transfer hydrogenation (or hydrogenation) of N‐heterocycles to store H₂, using formic acid or external hydrogen as a hydrogen source. The catalytic performance of ISAS‐Co/OPNC in both reactions surpasses previously reported homogeneous and heterogeneous precious‐metal catalysts. The reaction mechanisms are systematically investigated using first‐principles calculations and it is suggested that the Eley–Rideal mechanism is dominant.     

单原子催化:沟通均相催化与多相催化的桥梁（英文）

催化在现代化学工业中占据着极为重要的地位.催化剂是催化过程的核心.均相催化剂由于具有均一、孤立的活性位点,往往具有高活性与高选择性;但是分离困难限制了其实际应用.多相催化剂由于金属原子利用效率低、活性组分不均匀,活性与选择性相对较低;但其稳定易分离的特点使得目前大多数工业催化过程都是多相催化过程.近年来,单原子催化逐渐成为催化领域新的研究热点与前沿,受到相关研究人员的广泛关注.作为一种多相催化剂,单原子催化剂具有稳定易分离的优势.此外,单原子催化剂具有类似均相催化剂的孤立活性位点,可能具有高活性与高选择.因此单原子催化的概念一经提出,便被认为有望成为架起多相催化与均相催化的桥梁;但几年来并未从实验上得到证实.2016年开始,逐渐有单原子催化剂在经典均相催化反应过程中的应用报道,为该观点提供了实验上的证据.本综述概述了2016至2017年单原子催化剂在典型均相催化反应中的成功应用,包括:1)氢甲酰化反应.以烯烃和合成气为原料合成精细化学品醛类化合物的氢甲酰化反应是目前化工生产中典型的均相催化反应之一.2016年,张涛课题组和曾杰课题组先后报道了Rh/ZnO和Rh/CoO单原子催化剂在该反应中的成功应用.催化剂都表现出优异的催化性能,活性与经典均相Wilkinson’s催化剂相当;2)氢硅加成反应.作为合成有机硅产品的重要反应之一,工业上硅氢加成反应主要由Pt基均相催化剂催化.2016年Beller课题组首次报道了将Pt/Al_2O_3单原子催化剂用于烯烃硅氢加成反应中.该催化剂除表现出良好的催化活性和区域选择性外,还具有较高的稳定性和底物普适性;3)C–H键选择性氧化.烷烃部分氧化反应在学术研究和工业应用方面都有重要意义.刘文刚等将M-N-C单原子催化剂(其中M为Fe,Co等金属)成功应用于C–H键的活化反应中,并对催化剂的结构进行了深入剖析.以上实例表明通过调控金属与载体组合、设计开发合适的单原子催化剂,可以达到结合均相催化高活性、高选择性与多相催化稳定易分离的目的,为均相催化多相化提供了一条新途径,也证明单原子催化可望成为沟通均相催化与多相催化的桥梁.     

单原子催化中的活性位构建方法研究进展

近年来,单原子催化剂因具有多相催化剂的结构稳定、易分离和均相催化剂的“孤立位点”等潜在优点而受到了人们的广泛关注.因此我们着重对比说明了单原子催化剂多种制备方法的形成机制以及制备过程的优缺点,并结合相应反应对其催化活性、催化机理进行介绍.通过对单原子催化剂的制备研究现状的概述,以期对加快其工业化进程起到积极的促进作用.     

Carbonylation of Alkynes,Alkenes and Alcohols using Metal Complex Catalysts

Carbonylation of olefins, alcohols and halides using homogeneous as well as heterogeneous catalysts has been discussed. Highlights of contributions on the activity, selectivity and stability of catalysts for carbonylation reactions are discussed. Kinetics and mechanism including characterization of the intermediate catalytic species has also been reviewed. The performance of anchored Pd complexes on mesoporous supports (MCM-41 and MCM-48), water soluble Pd complexes and supported Pd catalysts in carbonylation of aryl alcohols and olefins has been discussed in the context of catalyst-product separation. Some aspects of kinetic modelling and reaction engineering of these multiphase catalytic reactions have also been reviewed.     

分子筛膜包覆型催化剂的制备和应用

均匀、连续、致密分子筛膜的合成和应用受到广泛关注。利用分子筛膜具有的筛分和催化作用,在传统颗粒催化剂或载体表面包覆分子筛膜形成复合型催化剂,可以实现膜基分离和催化过程的耦合,增加反应物选择性,提高目标产物收率。本文综述了近年来在不同类型颗粒催化剂或载体表面合成分子筛膜的制备方法,描述了分子筛膜包覆型复合催化剂用于不同催化反应体系的研究结果。同时,在归纳和总结已有研究成果基础上展望了分子筛膜包覆型催化剂的研究发展趋势。     

Bifunctional Catalysts Containing Zn(II) and Imidazolium Salt Ionic Liquids for Chemical Fixation of Carbon Dioxide

Zn(II) can efficiently promote the catalytic performance of imidazolium salt ionic liquids (imi-ILs) for the chemical fixation of CO₂ into epoxides. To obtain sustainability, immobilized bifunctional catalysts containing both imi-ILs and Zn(II) were prepared using bimodal mesoporous silica (BMMs) as carrier, through grafting of Zn(OAc)₂ and 1-(trimethoxysilyl)propyl-3-methylimidazolium chloride (Si-imi) separately in the nanopores. The catalysts, named as BMMs−Zn&ILs, were identified as efficient catalysts for cycloaddition reaction of CO₂ into epoxides under solvent-free conditions. BMMs−Zn&ILs showed good catalytic activity, which increased with the increase of the molar ratio of Zn(II) to Si-imi. As a comparison, different catalytic systems including homogeneous imi-IL, BMMs-ILs and BMMs−Zn were studied to demonstrate different cooperation behaviors. Furthermore, the kinetics studies of homogeneous and heterogeneous bifunctional catalysts were employed to confirm the differences, as well as to support the proposed cooperative catalysis mechanism in the nanopores.     

Noble metal-free catalysts for oxygen reduction reaction

Developing noble metal-free catalysts with low cost, high performance and stability for oxygen reduction reaction(ORR) in fuel cells is of great interest to promote sustainable energy devices. In this review, we summarized noble metal-free catalysts for ORR,including non-noble metal-based and heteroatom-doped carbon nanomaterials. Mesoporous structure, homogeneous distribution of nanocrystals and synergistic effect of carbon base and nanocrystals/doped heteroatoms have great effect on the ORR property.The noble metal-free nanomaterials showed comparable catalytic property, better stability and methanol tolerance than commercial platinum(Pt)-based catalysts, showing great potential as substitutes for noble metal-based catalysts. In addition, the challenges and chances of developing noble metal-free ORR catalysts are also discussed.     

Reactivity and Recyclability of Ligand-Protected Metal Cluster Catalysts for CO2 Transformation

It remains a significant challenge to construct an integrated catalyst that combines advantages of homogeneous and heterogeneous catalysis with clarified mechanism and high performance. Here we show atomically precise CuAg cluster catalysts for CO₂ capture and utilization, where two functional units are combined into the clusters: metal and ligand. Due to atomic resolution on total and local structures of such catalysts to be achieved, which disentangles heterogeneous imprecise systems and permits tracing the reaction processes via experiments coupled with theory, site-specific catalysis induced by metal-ligand synergy can be accurately elucidated. The CuAg cluster catalysts exhibit excellent reactivity and recyclability to forge the C−N bonding from CO₂ formylation with secondary amines that can make the cluster catalysts more unique compared with typically homogeneous complexes.     

Catalytic Performance of Ruthenium‐Supported Ionic‐Liquid Catalysts in Sustainable Synthesis of Macrocyclic Lactones

Thirteen‐ to eighteen‐membered lactones were synthesized by ring‐closing olefin‐metathesis reactions of bis‐olefins with heterogeneous Grubbs‐supported ionic‐liquid catalysts (SILCs), in which homogeneous Grubbs catalysts were confined in pores of alumina with the aid of an ionic liquid. The Grubbs‐SILCs exhibited higher catalytic performance than their homogeneous counterparts and could be repeatedly recovered by simple filtration and re‐used several times.     

Continuous homogeneous asymmetric transfer hydrogenation of ketones: lessons from kinetics

Is polymer enlargement of homogeneous catalysts a tedious task? Is not batch operation with homogeneous catalysts the optimum performance point for homogeneous catalysis? Is kinetic modelling relevant to more than academic questions in homogeneous catalysis? Can all answers for a given system be answered satisfactory? In the authors’ view, answers to these questions are no, no, yes, and depends. Polymer enlargement allowed the continuous operation of transfer hydrogenation in a chemical membrane reactor with total turnover numbers of up to 2.6×10³ and a space–time yield of 0.58 kg L^?1 d^?1 with an enantiomeric ratio of 26.8 (enantiomeric excess 92.8 %) for a conversion level of 80 %. This was predicted from simulation conducted with a model from kinetic batch experiments adopted for continuous application. These simulations for the polymer‐enlarged and the unmodified catalyst show that achieving comparable performance cannot be obtained by batch operation.     

Bimetallic dendrimer-encapsulated nanoparticles as catalysts: a review of the research advances

Bimetallic dendrimer-encapsulated nanoparticles (DENs) are important materials, because they have demonstrated improvement in performance compared to the monometallic DENs in many systems when they are used as catalysts. This tutorial review focuses on the recent research advances in bimetallic DENs with respect to their synthesis, characterization, and applications as catalysts. Bimetallic DENs can be made mainly via three routes: co-complexation, sequential loading, and partial displacement. The research in bimetallic DENs has been significantly promoted by the advancement of characterization instruments. The performances of bimetallic DENs as homogeneous and heterogeneous catalysts in organic synthesis have been compared with both monometallic DENs and their physical mixtures. It is concluded that the synergistic electronic effect in bimetallic nanoparticles enhances their catalytic activities.     

Distinguishing homogeneous from heterogeneous catalysis in electrode-driven water oxidation with molecular iridium complexes

Molecular water-oxidation catalysts can deactivate by side reactions or decompose to secondary materials over time due to the harsh, oxidizing conditions required to drive oxygen evolution. Distinguishing electrode surface-bound heterogeneous catalysts (such as iridium oxide) from homogeneous molecular catalysts is often difficult. Using an electrochemical quartz crystal nanobalance (EQCN), we report a method for probing electrodeposition of metal oxide materials from molecular precursors. Using the previously reported [Cp*Ir(H(2)O)(3)](2+) complex, we monitor deposition of a heterogeneous water oxidation catalyst by measuring the electrode mass in real time with piezoelectric gravimetry. Conversely, we do not observe deposition for homogeneous catalysts, such as the water-soluble complex Cp*Ir(pyr-CMe(2)O)X reported in this work. Rotating ring-disk electrode electrochemistry and Clark-type electrode studies show that this complex is a catalyst for water oxidation with oxygen produced as the product. For the heterogeneous, surface-attached material generated from [Cp*Ir(H(2)O)(3)](2+), we can estimate the percentage of electroactive metal centers in the surface layer. We monitor electrode composition dynamically during catalytic turnover, providing new information on catalytic performance. Together, these data suggest that EQCN can directly probe the homogeneity of molecular water-oxidation catalysts over short times.     

Triphenylphosphine-Based Covalent Organic Frameworks and Heterogeneous Rh-P-COFs Catalysts

The synthesis of phosphine-based functional covalent organic frameworks (COFs) has attracted great attention recently. Herein, we present two examples of triphenylphosphine-based COFs (termed P-COFs) with well-defined crystalline structures, high specific surface areas, and good thermal stability. Furthermore, rhodium catalysts with these P-COFs as support material show high turnover frequency for the hydroformylation of olefins, as well as excellent recycling performance. This work not only extends the phosphine-based COF family, but also demonstrates their application in immobilizing homogeneous metal-based (e.g., Rh-phosphine) catalysts for application in heterogeneous catalysis.     

手性树状分子膦配体在不对称催化氢化中的应用

树状大分子作为一类组成精确的超支化结构大分子,近十多年来引起了科学家们的广泛关注.作为一类新型可溶性载体应用于均相催化剂,尤其是手性均相催化剂的负载化研究是树状大分子的重要应用领域之一.本文主要介绍了手性树状大分子膦配体,包括膦配体位于树状分子核心、末端和表面的几种类型,重点对它们与金属配合物形成的催化剂在不对称催化氢化反应中的应用研究进行总结,同时对负载催化剂的分离与回收、树状分子载体的结构和体积对催化剂性能的影响进行了讨论.