Anionic tethered N-heterocyclic carbene chemistry

Since the discovery of a stable "bottleable" N-heterocyclic carbene (NHC), there has been a spectacular explosion of interest in this ligand class. This interest stems from a desire to understand the fundamentals of the structure and bonding of these systems, but also because of their numerous and emerging applications in small molecule activation, homogeneous catalysis and Lewis acid-catalysed reactions. In this Tutorial Review, we introduce the reader to NHCs, cover general synthetic methods to prepare anionic tethered NHCs and their metal complexes, and discuss emerging applications in reactivity and catalytic studies.     

Metal-Metal Cooperation in Dinucleating Complexes Involving Late Transition Metals Directed towards Organic Catalysis

Cooperatively bimetallic organic catalysis,coupling actions of two metal centers in a catalytic organic transformation via co-activation of a single molecule or synergistic activation of two molecules,has witnessed rapid development in the last decades.     

New Designs for Phototherapeutic Transition Metal Complexes

In this Minireview, we highlight recent advances in the design of transition metal complexes for photodynamic therapy (PDT) and photoactivated chemotherapy (PACT), and discuss the challenges and opportunities for the translation of such agents into clinical use. New designs for light‐activated transition metal complexes offer photoactivatable prodrugs with novel targeted mechanisms of action. Light irradiation can provide spatial and temporal control of drug activation, increasing selectivity and reducing side‐effects. The photophysical and photochemical properties of transition metal complexes can be controlled by the appropriate choice of the metal, its oxidation state, the number and types of ligands, and the coordination geometry.     

Methandiide as a Non‐Innocent Ligand in Carbene Complexes: From the Electronic Structure to Bond Activation Reactions and Cooperative Catalysis

The synthesis of a ruthenium carbene complex based on a sulfonyl‐substituted methandiide and its application in bond activation reactions and cooperative catalysis is reported. In the complex, the metal–carbon interaction can be tuned between a Ru?C single bond with additional electrostatic interactions and a Ru?C double bond, thus allowing the control of the stability and reactivity of the complex. Hence, activation of polar and non‐polar bonds (O?H, H?H) as well as dehydrogenation reactions become possible. In these reactions the carbene acts as a non‐innocent ligand supporting the bond activation as nucleophilic center in the 1,2‐addition across the metal–carbon double bond. This metal–ligand cooperativity can be applied in the catalytic transfer hydrogenation for the reduction of ketones. This concept opens new ways for the application of carbene complexes in catalysis.     

Direct functionalisation of group 10 N-heterocyclic carbene complexes for diversity enhancement

The synthesis of alkyne-substituted N-heterocyclic carbene complexes of Pd(II) and Pt(II) is reported. Catalyzed 1,3-dipolar cycloaddition with azides has been applied as a modular way of functionalisation of group 10 transition metal NHC complexes to generate potentially new metallodrugs.     

Bioorthogonal Catalytic Activation of Platinum and Ruthenium Anticancer Complexes by FAD and Flavoproteins

Recent advances in bioorthogonal catalysis promise to deliver new chemical tools for performing chemoselective transformations in complex biological environments. Herein, we report how FAD (flavin adenine dinucleotide), FMN (flavin mononucleotide), and four flavoproteins act as unconventional photocatalysts capable of converting Pt^IV and Ru^II complexes into potentially toxic Pt^II or Ru^II?OH₂ species. In the presence of electron donors and low doses of visible light, the flavoproteins mini singlet oxygen generator (miniSOG) and NADH oxidase (NOX) catalytically activate Pt^IV prodrugs with bioorthogonal selectivity. In the presence of NADH, NOX catalyzes Pt^IV activation in the dark as well, indicating for the first time that flavoenzymes may contribute to initiating the activity of Pt^IV chemotherapeutic agents.     

Activation of Carboxylic Acids in Asymmetric Organocatalysis

Organocatalysis, catalysis using small organic molecules, has recently evolved into a general approach for asymmetric synthesis, complementing both metal catalysis and biocatalysis. 1 Its success relies to a large extent upon the introduction of novel and generic activation modes. 2 Remarkably though, while carboxylic acids have been used as catalyst directing groups in supramolecular transition‐metal catalysis, 3 a general and well‐defined activation mode for this useful and abundant substance class is still lacking. Herein we propose the heterodimeric association of carboxylic acids with chiral phosphoric acid catalysts as a new activation principle for organocatalysis. This self‐assembly increases both the acidity of the phosphoric acid catalyst and the reactivity of the carboxylic acid. To illustrate this principle, we apply our concept in a general and highly enantioselective catalytic aziridine‐opening reaction with carboxylic acids as nucleophiles.     

镍N-杂环卡宾配合物在均相催化偶联反应中的应用

 近十几年来, N-杂环卡宾的配位化学和金属有机化学发展迅速, 已成为均相催化反应中研究最为广泛的配体之一. 在许多过渡金属催化的有机合成反应中特别是偶联反应中, N-杂环卡宾与传统有机膦配体相比具有较高的反应性. 镍价格低廉, 在很多反应中有望替代贵金属钯催化剂. 本文总结了镍 N-杂环卡宾化合物在催化交叉偶联反应和还原偶联反应中的最新应用进展.     

Transition‐Metal‐Free Decarboxylative Propargylic Substitution/Cyclization with either Azolium Enolates or Acyl Anions

Presented herein is an unprecedented transition‐metal‐free propargylic substitution reaction with either azolium enolates or acyl anions, which are generated from aldehydes under N‐heterocyclic carbene catalysis. This new catalytic activation operates on readily available cyclic propargylic carbamates through decarboxylation, and generates reactive allene intermediates that can undergo divergent cyclization pathways to deliver skeletally diverse polycyclic compounds with high levels of efficiency and excellent enantioselectivities.     

Soft Matter Approaches for Enhancing the Catalytic Capabilities of Polyoxometalate Clusters

In this minireview, we discuss the recent efforts on expanding the catalytic capabilities of polyoxometalates (POM) through emulsion catalysis approaches with novel catalytic-active POM–organic hybrid clusters as emulsifiers. The hybrid emulsifiers include surfactant encapsulated POM complexes, molecular POMs–organic hybrids, and POM-based solid nanoparticles. With such novel approaches the catalytic efficiency of the POMs can be significantly improved by enhancing the compatibility of the POMs with organic media, providing catalytic interface for biphasic reactions, as well as easier preparation, and better recyclability. Particularly, a simple, green chemistry method to prepare metal nanoparticle materials with POMs as both reducing and capping agents in aqueous is reviewed.     

Low-Valent Metals in Metal-Organic Frameworks Via Post-Synthetic Modification

Metal-organic frameworks (MOFs) provide uniquely tunable, periodic platforms for site-isolation of reactive low-valent metal complexes of relevance in modern catalysis, adsorptive applications, and fundamental structural studies. Strategies for integrating such species in MOFs include post-synthetic metalation, encapsulation and direct synthesis using low-valent organometallic complexes as building blocks. These approaches have each proven effective in enhancing catalytic activity, modulating product distributions (i.e., by improving catalytic selectivity), and providing valuable mechanistic insights. In this minireview, we explore these different strategies, as applied to isolate low-valent species within MOFs, with a particular focus on examples that leverage the unique crystallinity, permanent porosity and chemical mutability of MOFs to achieve deep structural insights that lead to new paradigms in the field of hybrid catalysis.     

离子液体和水: 构建高效绿色的纳米粒子催化体系

金属纳米粒子-保护剂-绿色溶剂体系, 因其高效、绿色, 且易实现反应产物和催化体系分离而备受关注. 新型的纳米粒子催化体系设计空间大, 通过设计纳米粒子、保护剂、功能化溶剂可以实现不同的反应和工艺要求, 也更符合低毒、高效可循环等绿色化学的理念. 本文结合作者课题组设计的纳米粒子-保护剂-绿色溶剂催化体系实现的一系列反应, 回顾了这个绿色的新催化体系发展的过程.     

Electron microscopic imaging of a single Group 8 metal atom catalyzing C-C bond reorganization of fullerenes

Heating a bulk sample of [60]fullerene complexes, (η(5)-C(5)H(5))MC(60)R(5) (M = Fe, Ru, R = Me, Ph), produces small hydrocarbons because of coupling of R and C(5)H(5) via C-C and C-H bond activation. Upon observation by transmission electron microscopy, these complexes, encapsulated in single-walled carbon nanotubes, underwent C-C bond reorganization reactions to form new C-C bond networks, including a structure reminiscent of [70]fullerene. Quantitative comparison of the electron dose required to effect the C-C bond reorganization of fullerenes and organofullerenes in the presence of a single atom of Ru, Fe, or Ln and in the the absence of metal atoms indicated high catalytic activity of Ru and Fe atoms, as opposed to no catalytic activity of Ln. Organic molecules such as hydrocarbons and amides as well as pristine [60]fullerene maintain their structural integrity upon irradiation by ca. 100 times higher electron dose compared to the Ru and Fe organometallics. The results not only represent a rare example of direct observation of a single-metal catalysis but also have implications for the use of single metal atom catalysis in Group 8 metal heterogeneous catalysis.     

Recent advances in annulations enabled by nucleophilic Lewis base/metal dual catalysis

Metal/nucleophilic Lewis base dual catalysis has been recognized as a reliable and promising strategy for finishing ideal organic synthesis over the past decades. The new strategy can usually achieve some chemical reactions that cannot be realized by the traditionally mono-catalytic system, dramatically expanding the synthetic utility of chemical transformations by leveraging additional activation modes. Thus considerable progress has been made in the synthesis of a wide range of heterocyclic and biologically active compounds by using the combination of diversely metal/nucleophilic Lewis base dual catalysts, including metal/phosphine, metal/N-heterocyclic carbene (NHC) and metal/tertiary amine dual catalysis systems. In this review, we describe a comprehensive and updated advance of metal/nucleophilic Lewis base dual catalytic annualtion reactions, meanwhile, the related mechanism and the application of these annulation strategies in natural product total synthesis will be highlighted in detail.     

Leveraging Metal and Ligand Reactive Sites for One Pot Reactions: Ligand-Centered Borenium Ions for Tandem Catalysis with Palladium

Tandem catalysts that perform two different organic transformations in a single pot are highly desirable because they enable rapid and efficient assembly of simple organic building blocks into more complex molecules. Many examples of tandem catalysis rely on metal-catalyzed reactions involving one or more metal complexes. Remarkably, despite surging interest in the development of chemically reactive (i. e., non-innocent) ligands, there are few examples of metal complexes that leverage ligand-centered reactivity to perform catalytic reactions in tandem with separate catalytic reactions at the metal. Here we report how multifunctional Pd complexes with triaminoborane-derived diphosphorus ligands, called TBDPhos, appear to facilitate borenium-catalyzed cycloaddition reactions at the ligand, and Pd-catalyzed Stille and Suzuki cross-coupling reactions at the metal. Both transformations can be accessed in one pot to afford rare examples of tandem catalysis using separate metal and ligand catalysis sites in a single complex.     

环钯化合物合成及其在催化中的应用

环钯化合物由于丰富的结构、高度的稳定性和卓越的催化性能,已成为钯化学研究的热点之一。迄今已开发出了C-H键活化、氧化加成、转金属化、亲核加成和配体交换等多种方法,可制备出从三元环到十一元环的CY型环钯化合物和多种YCY型环钯化合物。环钯化合物目前已应用于偶联、烯烃氢化和不对称催化等反应中。本文简单介绍了环钯化合物的种类,重点介绍了环钯化合物的合成方法和催化应用情况,最后提出了环钯化合物在今后合成研究和催化应用中的发展建议。     

Structure and Reactivity of Late Transition Metal η3‐Benzyl Complexes

The coordination of transition metals to organic fragments can yield complexes with fascinating and unexpected binding patterns. The study of metal‐benzyl complexes has demonstrated the feasibility of η³‐coordination, which results in a dearomatized ring. These complexes also offer insight into reaction mechanisms as proposed intermediates in catalytic cycles. In this Review we discuss the synthesis and characterization of these complexes with late transition metals and the subsequent development of catalytic benzylic functionalization methods, including asymmetric variants.     

Catalysis with cycloruthenated complexes

Cycloruthenated complexes have been studied extensively over the last few decades. Many accounts of their synthesis, characterisation, and catalytic activity in a wide variety of transformations have been reported to date. Compared with their non-cyclometallated analogues, cycloruthenated complexes may display enhanced catalytic activities in known transformations or possess entirely new reactivity. In other instances, these complexes can be chiral, and capable of catalysing stereoselective reactions. In this review, we aim to highlight the catalytic applications of cycloruthenated complexes in organic synthesis, emphasising the recent advancements in this field.

We discuss recent advances in the applications of cycloruthenated complexes in organic synthesis, comprising C–H activation, chiral-at-metal catalysis, Z-selective olefin metathesis, transfer hydrogenation, enantioselective cyclopropanations and cycloadditions.     

Asymmetric Borohydride Reduction of Acetophenone Catalyzed by Chiral Salen-Co(Ⅱ) Complex Using Sodium Borohydride

Development of efficient catalytic asymmetric reactions is the most challenging task in current synthetic chemistry; much effort has been devoted to create the chiral metal complexes of asymmetric catalysis. In the last two decades' many brand-new ligands had been synthesized and their combination with various metal ions has been applied in asymmetric catalysis. However, most ligands have only narrow applications and their use is limited to some reactions. Exceptionally, a few ligands and their metal complexes such as binaphthol, semicollin,and binap show wide applicability. Chiral salen ligand is one of such ligands and their metal complexes are now used as the catalysts for a variety of asymmetric reactions such as epoxidation^[1], aziridination^[2], cyclopropanation^[3], Diels-Alder reaction^[4], asymmetric transfer hydrogenation of aromatic ketones^[5] and kinetic resolution of racemic epoxides^[6] and so on.     

手性pybox-金属络合物及其在不对称催化反应中的应用

具有C2对称性的双噁唑啉型吡啶(pybox)是一类有效的手性配体,能与许多金属离子配位,其手性催化性能已得到越来越多的关注。本文综述了手性配体pybox和pybox-金属络合物的合成方法,特别是近年来pybox-金属络合物在不对称催化反应如不对称环丙烷化反应、不对称Diels-Alder反应、1,3-偶极环加成反应、不对称aldol反应等中应用的最新进展。