Probing Substrate Diffusion in Interstitial MOF Chemistry with Kinetic Isotope Effects

Metal–organic frameworks (MOFs) have garnered substantial interest as platforms for site‐isolated catalysis. Efficient diffusion of small‐molecule substrates to interstitial lattice‐confined catalyst sites is critical to leveraging unique opportunities of these materials as catalysts. Understanding the rates of substrate diffusion in MOFs is challenging, and few in situ chemical tools are available to evaluate substrate diffusion during interstitial MOF chemistry. Herein, we demonstrate nitrogen atom transfer (NAT) from a lattice‐confined Ru₂ nitride to toluene to generate benzylamine. We use the comparison of the intramolecular deuterium kinetic isotope effect (KIE), determined for amination of a partially deuterated substrate, with the intermolecular KIE, determined by competitive amination of a mixture of perdeuterated and undeuterated substrates, to establish the relative rates of substrate diffusion and interstitial chemistry. We anticipate that the developed KIE‐based experiments will contribute to the development of porous materials for group‐transfer catalysis.     

金属-有机骨架材料及其在催化反应中的应用

金属-有机骨架(metal-organic frameworks, MOFs)材料是由金属离子和有机配体通过自组装而成的具有多孔结构的特殊晶体材料。由于其种类的多样性、孔道的可调性和结构的易功能化,已在气体的吸附和分离、催化、磁学、生物医学等领域表现出了诱人的应用前景。本文介绍了MOFs材料的类型和常用的合成方法,综述了近年来MOFs材料在催化领域的应用,特别是以MOFs材料中骨架金属作为活性中心、骨架有机配体作为活性中心和负载催化活性组分的催化反应,并对MOFs材料的催化应用趋势做了展望,以期对MOFs材料的催化性能有比较全面的认识。     

金属-有机框架材料在催化炔烃半氢化反应中的应用

炔烃的半氢化反应在有机合成和精细化工领域具有重要地位,如何同时兼顾反应活性和选择性仍存在很大挑战。目前已有多种材料被应用于相关催化,其中金属-有机骨架(MOFs)及其复合材料受到越来越多关注。MOFs的多孔性、结构可修饰性、空间限域效应、协同催化等优点,使其在炔烃的半氢化反应中表现出独特的应用前景。本文综述了MOFs及其复合材料在炔烃的半氢化反应生成烯烃过程中的应用,主要根据活性催化位点的类别展开介绍,重点阐述了不同体系中催化效果和结构之间的关系。     

Engineering Metal–Organic Framework Catalysts for C−C and C−X Coupling Reactions: Advances in Reticular Approaches from 2014–2018

Metal–organic frameworks (MOFs) are a class of crystalline porous materials that have been actively used for several industrial and synthetic applications. MOFs are spatially and geometrically extrapolated coordination polymers with intriguing properties such as tunable porosity and dimensionality. In terms of their catalytic efficiency, MOFs combine the easy recoverability of heterogeneous catalysts with the increased selectivity of biological catalysts. It is therefore not surprising that a lot of work on optimizing MOF catalysts for organic transformations has been carried out over the past decade. In this review, recent developments in MOF catalysis are summarized, with special attention being paid to C−C, C−N, and C−O coupling reactions. The influence of pore size, pore environment, and load on catalytic activity is described. Post-synthetic stabilization techniques and host–guest interactions in caged MOF scaffolds are detailed. Mechanistic aspects pertaining to the use of MOFs in asymmetric heterogeneous catalysis are highlighted and categorized.     

Catalysis by metal-organic frameworks: fundamentals and opportunities

Crystalline porous materials are extremely important for developing catalytic systems with high scientific and industrial impact. Metal-organic frameworks (MOFs) show unique potential that still has to be fully exploited. This perspective summarizes the properties of MOFs with the aim to understand what are possible approaches to catalysis with these materials. We categorize three classes of MOF catalysts: (1) those with active site on the framework, (2) those with encapsulated active species, and (3) those with active sites attached through post-synthetic modification. We identify the tunable porosity, the ability to fine tune the structure of the active site and its environment, the presence of multiple active sites, and the opportunity to synthesize structures in which key-lock bonding of substrates occurs as the characteristics that distinguish MOFs from other materials. We experience a unique opportunity to imagine and design heterogeneous catalysts, which might catalyze reactions previously thought impossible.     

金属-有机骨架材料在烯烃氧化中的应用

本文分别从以骨架中的金属(金属簇)为催化中心的MOF材料、利用具有催化活性的刚性有机配合物构筑的MOF材料和MOF负载催化材料三个方面详细介绍了MOF作为催化剂在烯烃氧化反应中的应用情况,分析了其各自的优缺点。具有催化活性的刚性有机配合物构筑的MOF材料稳定性较好,能够引入具有光学活性的催化剂,可以作为不对称催化氧化催化剂使用,是未来的一个研究发展方向。     

Metal–Organic Framework (MOF)-Based Materials as Heterogeneous Catalysts for C−H Bond Activation

Converting light hydrocarbons such as methane, ethane, propane, and cyclohexane into value-added chemicals and fuel products by means of direct C−H functionalization is an attractive method in the petrochemical industry. As they emerge as a relatively new class of porous solid materials, metal–organic frameworks (MOFs) are appealing as single-site heterogeneous catalysts or catalytic supports for C−H bond activation. In contrast to the traditional microporous and mesoporous materials, MOFs feature high porosity, functional tunability, and molecular-level characterization for the study of structure–property relationships. These virtues make MOFs ideal platforms to develop catalysts for C−H activation with high catalytic activity, selectivity, and recyclability under relatively mild reaction conditions. This review highlights the research aimed at the implementation of MOFs as single-site heterogeneous catalysts for C−H bond activation. It provides insight into the rational design and synthesis of three types of stable MOF catalysts for C−H bond activation, that is, i) metal nodes as catalytic sites, ii) the incorporation of catalytic sites into organic struts, and iii) the incorporation of catalytically active guest species into pores of MOFs. Here, the rational design and synthesis of MOF catalysts that lead to the distinct catalytic property for C−H bond activation are discussed along with the post-synthesis of MOFs, intriguing functions with MOF catalysts, and microenvironments that lead to the distinct catalytic properties of MOF catalysts.     

Multi-functional sites catalysts based on post-synthetic modification of metal-organic frameworks

Multi-functional sites MOFs have been explored as a new type of heterogeneous catalytic materials, which can be constructed by various post-synthetic modifications.     

高稳定性金属有机骨架UiO-66的合成与应用

金属有机骨架(metal-organic frameworks,MOFs)是一种由金属中心与有机配体自组装而成的、具有三维网状有序孔结构的新型多孔晶体材料,其具有超高的比表面积、种类和结构多样性、可化学功能化等特点,在多个研究领域显示出了潜在的应用前景,已成为当前化学、材料学科的研究热点之一。 然而大多数MOFs材料的稳定性较差,极大地束缚了MOFs材料的发展。 以Zr为金属中心,对苯二甲酸为有机配体的UiO-66具有较好的热稳定性,结构可在500 ℃保持稳定,并且其还具有很高的耐酸性和一定的耐碱性,引起了人们的关注。 本文主要综述了UiO-66在合成调控、功能化合成和后改性方面的研究现状,以及其在吸附和催化等领域的应用前景。     

Atomically Dispersed Metal Sites in MOF‐Based Materials for Electrocatalytic and Photocatalytic Energy Conversion

Metal sites play an essential role in both electrocatalytic and photocatalytic energy conversion. The highly ordered arrangements of the organic linkers and metal nodes as well as the well‐defined pore structures of metal‐organic frameworks (MOFs) make them ideal substrates to support atomically dispersed metal sites (ADMSs) located in their metal nodes, linkers, and pores. Porous carbon materials doped with ADMSs can be derived from these ADMS‐incorporating MOF precursors through controlled treatments. These ADMSs incorporated in pristine MOFs and MOF‐derived carbon materials possess unique advantages over molecular or bulk metal‐based catalysts and bridge the gap between homogeneous and heterogeneous catalysts for energy‐conversion applications. This Review presents recent progress in the design and incorporation of ADMSs in MOFs and MOF‐derived materials for energy‐conversion applications.     

金属有机框架膜的制备及应用

金属有机框架化合物是一类新颖的纳米孔结晶材料,其由金属离子或簇以强的配位键形式连接多种多样的有机配体构成．金属有机框架化合物的均一孔径、高比表面积和吸附亲和力等独特的结构特点使其在组装成具有优异性能的膜方面具有很强的吸引力．金属有机框架膜在基础理论和实际应用方面显示了巨大的潜力．本文主要介绍近年来关于金属有机框架膜的制备及其在分离、化学传感、催化和电化学中的应用等研究,同时指出了目前需要克服的问题．     

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.     

Flexible and Hierarchical Metal–Organic Framework Composites for High‐Performance Catalysis

The development of porous composite materials is of great significance for their potentially improved performance over those of individual components and extensive applications in separation, energy storage, and heterogeneous catalysis. Now mesoporous metal–organic frameworks (MOFs) with macroporous melamine foam (MF) have been integrated using a one‐pot process, generating a series of MOF/MF composite materials with preserved crystallinity, hierarchical porosity, and increased stability over that of melamine foam. The MOF nanocrystals were threaded by the melamine foam networks, resembling a ball‐and‐stick model overall. The resulting MOF/MF composite materials were employed as an effective heterogeneous catalyst for the epoxidation of cholesteryl esters. Combining the advantages of interpenetrative mesoporous and macroporous structures, the MOF/melamine foam composite has higher dispersibility and more accessibility of catalytic sites, exhibiting excellent catalytic performance.     

金属-有机框架作为异相催化剂的表征方法概述

作为一类具有大的比表面积、高孔隙率、合成方便、骨架规模可变、化学可修饰以及结构组成多样等优点的新型多孔材料,金属-有机框架（MOFs）在光电材料、药物传输、气体吸附分离及催化等领域有着广阔的应用前景,成为近年来研究的热点。异相催化是MOFs最具发展潜力的应用领域之一,各种表征方法和研究手段是开展MOFs异相催化研究的工作基础。本文主要围绕表征MOFs作为异相催化剂的常用技术手段进行介绍,包括X-射线单晶衍射、X-射线粉末衍射、热重分析、红外光谱/拉曼光谱分析、透射/扫描电镜等,旨在为开展相关MOFs催化研究提供一定参考。     

Identifying promising metal–organic frameworks for heterogeneous catalysis via high-throughput periodic density functional theory

Metal–organic frameworks (MOFs) are a class of nanoporous materials with highly tunable structures in terms of both chemical composition and topology. Due to their tunable nature, high-throughput computational screening is a particularly appealing method to reduce the time-to-discovery of MOFs with desirable physical and chemical properties. In this work, a fully automated, high-throughput periodic density functional theory (DFT) workflow for screening promising MOF candidates was developed and benchmarked, with a specific focus on applications in catalysis. As a proof-of-concept, we use the high-throughput workflow to screen MOFs containing open metal sites (OMSs) from the Computation-Ready, Experimental MOF database for the oxidative C—H bond activation of methane. The results from the screening process suggest that, despite the strong C—H bond strength of methane, the main challenge from a screening standpoint is the identification of MOFs with OMSs that can be readily oxidized at moderate reaction conditions. © 2019 Wiley Periodicals, Inc.     

Catalysis in Single Crystalline Materials: From Discrete Molecules to Metal-Organic Frameworks

Catalysis is one of the key techniques for people's modern life. It has created numerous essential chemicals such as biomedicines, agricultural chemicals and unique materials. Heterogeneous catalysis is the new emerging method with reusable catalysts. Among heterogenous catalysis patterns developed so far, single crystalline catalysis has become the promising one owing to its high catalytic density and selectivity resulted by the inherent porosity, orderliness of the lattices and permeability. These crystalline catalysts could be used in various reactions such as photo-dimerization, Diels-Alder reaction, CO₂ transformation and so on. In this review, we highlighted the reported works about the single crystalline catalysts. Both discrete small molecules and metal-organic frameworks (MOFs) have been used to prepare single crystals for catalysis. For discrete molecules based crystalline catalysts, coordinated and covalent molecules have been used. There were more catalytic modes in crystalline MOF catalysts. Three patterns were identified in this review: single crystalline MOFs i) without catalytic sites, ii) with inherent catalytic features and iii) with introducing catalytic units by post synthetic modification. Based on these examples, this review committed to provide the inspirations for the further design and application of single crystalline materials.     

Surface-Deactivated Core–Shell Metal–Organic Framework by Simple Ligand Exchange for Enhanced Size Discrimination in Aerobic Oxidation of Alcohols

Metal–organic frameworks (MOFs) are an attractive catalyst support for stable immobilization of the active sites in their scaffold due to the high tunability of organic ligands. The active site-functionalized ligands can be easily employed to construct MOFs as porous heterogeneous catalysts. However, the existence of active sites on the external surfaces as well as internal pores of MOFs seriously impedes the selective reaction in the pore. Herein, through a simple post-synthetic ligand exchange (PSE) method we synthesized surface-deactivated (only core-active) core–shell-type MOF catalysts, which contain 2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) groups on the ligand as active sites for aerobic oxidation of alcohols. The porous but catalytically inactive shell ensured the size-selective permeability by sieving effects and induced all reactions to take place in the pores of the catalytically active core. Because PSE is a facile and universal approach, this can be rapidly applied to a variety of MOF-based catalysts for enhancing reaction selectivity.     

Template‐Induced Diverse Metal–Organic Materials as Catalysts for the Tandem Acylation–Nazarov Cyclization

In our continuing quest to develop a metal–organic framework (MOF)‐catalyzed tandem pyrrole acylation–Nazarov cyclization reaction with α,β‐unsaturated carboxylic acids for the synthesis of cyclopentenone[b]pyrroles, which are key intermediates in the synthesis of natural product (±)‐roseophilin, a series of template‐induced Zn‐based ( 1–3 ) metal‐organic frameworks (MOFs) have been solvothermally synthesized and characterized. Structural conversions from non‐porous MOF 1 to porous MOF 2 , and back to non‐porous MOF 3 arising from the different concentrations of template guest have been observed. The anion–π interactions between the template guests and ligands could affect the configuration of ligands and further tailor the frameworks of 1–3 . Futhermore, MOFs 1–3 have shown to be effective heterogeneous catalysts for the tandem acylation–Nazarov cyclization reaction. In particular, the unique structural features of 2 , including accessible catalytic sites and suitable channel size and shape, endow 2 with all of the desired features for the MOF‐catalyzed tandem acylation–Nazarov cyclization reaction, including heterogeneous catalyst, high catalytic activity, robustness, and excellent selectivity. A plausible mechanism for the catalytic reaction has been proposed and the structure–reactivity relationship has been further clarified. Making use of 2 as a heterogeneous catalyst for the reaction could greatly increase the yield of total synthesis of (±)‐roseophilin.     

Enlightening the journey of metal-organic framework (derived) catalysts during the oxygen evolution reaction in alkaline media via operando X-ray absorption spectroscopy

The development of catalysts with enhanced activity for the oxygen evolution reaction (OER) compared to the traditionally used metal oxide catalysts is crucial for further commercialization of electrolyzers. Because of their high surface area and adjustable pore structure, metal-organic framework (MOF)-based catalysts represent a promising alternative. During the OER in alkaline media, the initial MOF structure is susceptible to transformations including the decomposition of the organic backbone and/or the formation of oxide, hydroxide and oxyhydroxide intermediates. Hence, operando characterizations of MOF catalysts during OER are essential to understand the material's progressive changes and extract the OER catalytic mechanism. This article discusses existing operando X-ray absorption spectroscopy studies of MOF(-derived) catalysts during OER and extracts important parameters for future research regarding operando X-ray absorption spectroscopy characterizations of MOFs during alkaline electrolysis.     

UiO-67-Sal-CuCl2在空气中催化芳香醇的选择性氧化

利用水热法一步合成了金属有机骨架(MOFs)材料UiO-67-Sal, 并将3种铜盐固定在其表面, 研究了3种铜MOFs材料催化芳香醇选择性氧化的性能. 结果表明, UiO-67-Sal-CuCl₂催化剂对芳香醇选择性氧化反应具有良好的催化活性, 且在重复使用4次后, 依然保持较好的催化效果.