Dual Gold Catalysis: σ,π‐Propyne Acetylide and Hydroxyl‐Bridged Digold Complexes as Easy‐To‐Prepare and Easy‐To‐Handle Precatalysts

A series of dinuclear gold σ,π‐propyne acetylide complexes were prepared and tested for their catalytic ability in dual gold catalysis that was based on the reaction of an electrophilic π‐complex of gold with a gold acetylide. The air‐stable and storable catalysts can be isolated as silver‐free catalysts in their activated form. These dual catalysts allow a fast initiation phase for the dual catalytic cycles without the need for additional additives for acetylide formation. Because propyne serves as a throw‐away ligand, no traces of the precatalyst are generated. Based on the fast initiation process, side products are minimized and reaction rates are higher for these catalysts. A series of test reactions were used to demonstrate the general applicability of these catalysts. Lower catalyst loadings, faster reaction rates, and better selectivity, combined with the practicability of these catalysts, make them ideal catalysts for dual gold catalysis.     

Supported gold nanoparticles as catalysts for organic reactions

This critical review is intended to attract the interest of organic chemists and researchers on green and sustainable chemistry on the catalytic activity of supported gold nanoparticles in organic transformations. In the general part of this critical review, emphasis is given to the different procedures to form supported gold nanoparticles and to the importance of the support cooperating in the catalysis. Also the convergence of homogeneous and heterogeneous catalysis in the study of gold nanoparticles has been discussed. The core part of this review is constituted by sections in which the reactions catalyzed by supported gold nanoparticles are described. Special emphasis is made on the unique ability of gold catalysts to promote additions to multiple C-C bonds, benzannulations and alcohol oxidation by oxygen (282 references).     

Single-atom Catalysts Based on Layered Double Hydroxides

Single-atom catalysts(SACs) have attracted much attention for their superior catalytic performance in various fields. It has been widely accepted that the selection of appropriate substrates is crucial to the fabrication and application of SACs. Layered double hydroxides(LDHs) have been developed as one of the promising substrates for single-atoms due to their unique adjustable supramolecular structures. In this review, we comprehensively sort out the research of SACs based on LDHs. By analyzing the characteristics of LDHs and the single-atoms, respectively, the preparation strategies of SACs by using LDHs are summarized. Their applications as efficient catalysts in electrocatalysis, photocatalysis and thermal catalysis are then discussed. Finally, we summarize the opportunities and challenges for the rational design and application expansion of SACs based on LDHs in the future.     

Enantioselective C−H Functionalization Reactions under Gold Catalysis

Transition metal-catalyzed enantioselective functionalization of ubiquitous C−H bonds has proven to be promising field as it offers the construction of chiral molecular complexity in a step- and atom-economical manner. In recent years, gold has emerged as an attractive contender for catalyzing such reactions. The unique reactivities and selectivities offered by gold catalysts have been exploited to access numerous asymmetric transformations based on gold-catalyzed C−H functionalization processes. Herein, this review critically highlights the major advances and discoveries made in the enantioselective C−H functionalization under gold catalysis which is accompanied by mechanistic insights at appropriate places.     

Alkyne Difunctionalization by Dual Gold/Photoredox Catalysis

Highly selective tandem nucleophilic addition/cross‐coupling reactions of alkynes have been developed using visible‐light‐promoted dual gold/photoredox catalysis. The simultaneous oxidation of Au^I and coordination of the coupling partner by photo‐generated aryl radicals, and the use of catalytically inactive gold precatalysts allows for high levels of selectivity for the cross‐coupled products without competing hydrofunctionalization or homocoupling. As demonstrated in representative arylative Meyer–Schuster and hydration reactions, this work expands the scope of dual gold/photoredox catalysis to the largest class of substrates for gold catalysts and benefits from the mild and environmentally attractive nature of visible‐light activation.     

Electrochemical Gold-Catalyzed 1,2-Difunctionalization of C−C Multiple Bonds**

Herein, we disclose the first report of 1,2-difunctionalization of C−C multiple bonds using electrochemical gold redox catalysis. By adopting the electrochemical strategy, the inherent π-activation and cross-coupling reactivity of gold catalysis are harnessed to develop the oxy-alkynylation of allenoates under external-oxidant-free conditions. Detailed mechanistic investigations such as ³¹P NMR, control experiments, mass studies, and cyclic voltammetric (CV) analysis have been performed to support the proposed reaction mechanism.     

Gold-catalyzed cyanosilylation reaction: homogeneous and heterogeneous pathways

Gold had been considered to be an extremely inert metal, but recently it was found that nanometer-sized gold particles on metal-oxide supports acted as catalysts for simple organic reactions, such as oxidation and hydrogenation, even at or below room temperature. Herein, we report that gold nanoparticles (AuNPs) of zero oxidation state (Au0) are catalytically active for a C--C bond-forming reaction, the cyanosilylation of aldehydes. The AuNP-catalyzed cyanosilylation proceeded smoothly at room temperature with 0.2 wt % loading of AuNPs. The reactions of aromatic aldehydes were almost quantitative, except for benzaldehyde derivatives containing the electron-withdrawing NO2 group, and alpha,beta-unsaturated aromatic aldehydes were the most reactive substrates. The reactions also went smoothly for aliphatic aldehydes. Mechanistic studies indicated that the reactions proceeded both homogeneously and heterogeneously: homogeneous catalysis by leached gold species and heterogeneous catalysis by the adsorption of the reactants (aldehydes and trimethylsilyl cyanide) onto AuNPs. The ratio of homogeneous and heterogeneous catalysis was estimated to be approximately 4:1.     

Silicon–Nitrogen Bond Formation via Heterodehydrocoupling and Catalytic N-Silylation

Silicon–nitrogen bond formation is an important subfield in main group chemistry, and catalysis is an attractive route for efficient, selective formation of these bonds. Indeed, heterodehydrocoupling and N-silylation offer facile methods for the synthesis of small molecules through the coupling of primary, secondary, and tertiary silanes with N-containing substrates such as amines, carbazoles, indoles, and pyrroles. However, the reactivity of these catalytic systems is far from uniform, and critical issues are often encountered with product selectivity, conversions, substrate scope, catalyst activation, and in some instances, competing side reactions. Herein, a catalogue of catalysts and their reactivity for Si−N heterodehydrocoupling and N-silylation are reported.     

A Desulfonylative Approach in Oxidative Gold Catalysis: Regiospecific Access to Donor‐Substituted Acyl Gold Carbenes

Donor‐substituted acyl gold carbenes are challenging to access selectively by gold‐promoted intermolecular oxidation of internal alkynes as the opposite regioisomers frequently predominate. By using alkynyl sulfones or sulfonates as substrates, the oxidative gold catalysis in the presence of substituted pyridine N‐oxides offers regiospecific access to acyl/aryl, acyl/alkenyl, and acyl/alkoxy gold carbenes by in situ expulsion of sulfur dioxide. The intermediacies of these reactive species are established by their reactivities, including undergoing further oxidation by the same oxidant, cyclopropanation of styrenes, engaging in a [3+2] cycloaddition with α‐methylstyrene, and conversion into dienones.     

Thermal activation of molecularly-wired gold nanoparticles on a substrate as catalyst

The ability to prepare nanostructured metal catalysts requires the ability to control size and interparticle spatial and surface access properties. In this work, we report novel findings of an atomic force microscopic investigation of a controlled thermal activation strategy of gold catalysts nanostructured via molecular wiring or linking on a substrate surface. Gold nanocrystals of approximately 2 nm diameter capped by decanethiolate and wired by 1,9-nonanedithiolate on mica substrates were studied as a model system. By manipulating the activation temperature (200-250 degrees C), the capping/wiring molecules can be removed to produce controllable particle size and interparticle spatial morphology. The electrocatalytic activity of the activated nanostructures toward methanol oxidation, which is of fundamental importance to fuel cell catalysis, has been demonstrated. The novelty of the findings is the viability of a thermal activation strategy of core-shell nanostructured catalysts based on molecularly predefined interparticle spatial properties on a substrate, which upon further investigation may form the basis for spatially controllable nanostructured catalysts.     

Gold‐Catalyzed Cyclization Processes: Pivotal Avenues for Organic Synthesis

Over the years, gold catalysis has materialized as an incredible synthetic approach among the scientific community. Due to the trivial reaction conditions and great functional compatibility, these progressions are synthetically expedient, because practitioners can implement them to build intricate architectures from readily amassed building blocks with high bond forming indices. The incendiary growth of gold catalysts in organic synthesis has been demonstrated as one of the most prevailing soft Lewis acids for electrophilic activation of carbon‐carbon multiple bonds towards a great assortment of nucleophiles. Nowadays, organic chemists consistently employ gold catalysts to carry out a diverse array of organic transformations to build unprecedented molecular architectures. Despite all these achievements and a plethora of reports, many vital challenges remain. In this account, we describe the reactivity of various gold catalysts towards cyclization processes developed over the years. These protocols give access to a wide scope of polyheterocyclic structures, containing different medium‐sized ring skeletons. This is interesting, as the quest for highly selective reactions to assemble diversely functionalized products has attracted much attention. We envisage that these newly developed chemo‐, regio‐, and diastereoselective protocols could provide an expedient route to architecturally cumbersome heterocycles of importance for the pharmaceutical industry.     

Activation of N−O σ Bonds with Transition Metals: A Versatile Platform for Organic Synthesis and C−N Bonds Formation**

N−O σ bonds containing compounds are versatile substrates for organic synthesis under transition metal catalysis. Their ability to react through both polar (oxidative addition, formation of metallanitrene, nucleophilic substitution) and radical pathways (single electron transfer, homolytic bond scission) have triggered the development of various synthetic methodologies, particularly toward synthesizing nitrogen-containing compounds. In this review, we discuss the different modes of activation of N−O bonds in the presence of transition metal catalysts, emphasizing the experimental and computational mechanistic proofs in the literature to help to design new synthetic pathways toward the synthesis of C−N bonds.     

单分子层保护纳米 Au 粒子表面配位催化剂的制备及其应用

 贵金属纳米粒子由于其小尺寸效应而表现出特殊的催化性能. 综述了纳米 Au 粒子表面配位催化剂的制备方法及其在催化中的应用. 由于 Au 可与硫化物形成配位键, 所以硫化物可在 Au 表面形成有序单分子膜. 单分子膜保护的 Au 纳米粒子具有非常好的溶解性、分散性、稳定性, 以及由不同的表面功能团而导致的不同的催化性能. 该催化体系兼具均相催化剂和多相催化剂的特点, 这对开发新型催化剂具有重要的理论和实际意义.     

An Aluminum Fluoride Complex with an Appended Ammonium Salt as an Exceptionally Active Cooperative Catalyst for the Asymmetric Carboxycyanation of Aldehydes

Al−F bonds are among the most stable σ bonds known, exhibiting an even higher bond energy than Si−F bonds. Despite a stability advantage and a potentially high Lewis acidity of Al−F complexes, they have not been described as structurally defined catalysts for enantioselective reactions. We show that Al−F salen complexes with appended ammonium moieties give exceptional catalytic activity in asymmetric carboxycyanations. In addition to aromatic aldehydes, enal and aliphatic substrates are well accepted. Turnover numbers up to around 10⁴ were achieved, whereas with previous catalysts 10¹–10² turnovers were typically attained. In contrast to Al−Me and Al−Cl salen complexes, the analogous Al−F species are remarkably stable towards air, water, and heat, and can be recovered unchanged after catalysis. They possess a considerably increased Lewis acidity as shown by DFT calculations.     

N-heterocyclic carbenes in gold catalysis

The appealing properties of N-heterocyclic carbenes (NHC) as ancillary ligands and the high potential of gold as an organometallic catalyst have made their encounter inevitable. Still in its infancy, NHC-gold catalysis is nevertheless growing rapidly. In this tutorial review, catalytic transformations involving NHC-containing gold(i) and gold(iii) complexes are presented. Particular attention is drawn to the versatility and selectivity of these catalysts.     

Heterocycles from gold catalysis

The article reviews the most important developments in the synthesis of heterocycles by gold catalysts for reactions directly involving the heteroatoms in the reacting groups. Reactions without direct participation of the hetero atoms, for example in substrates with the heteroatom in a tether between the reacting groups, are not included. In the last decade homogeneous gold catalysis has emerged from a handful of scattered publications to a hot topic, an area with now hundreds of publications per year. Among the many different products accessible by the new methods developed, heterocycles are probably the most important class of compounds with significant impact on the synthesis of agrochemicals and pharmaceuticals.     

催化剂活性位本质和构效关系的模型催化研究

明确催化剂的活性位本质和构建多相催化的结构和反应性能之间的准确关系是催化基础研究的重点,表面科学研究基于丰富的表征测试手段能够较好地在分子原子水平测定表面结构以明确催化剂活性位本质,并通过高压原位反应池测定相关催化反应性能,获得较可靠的催化剂构效关系。本文简要总结了近年来本人参与的几个模型催化研究例子,包括贵金属表面上CO和烷烃催化氧化的活性表面、纳米Au膜的制备和CO氧化的催化活性位、VO_x/Pt(111)上丙烷氧化的协同作用、Au Pd合金上醋酸乙烯酯合成Au的助催化作用、模型氧化物上纳米Pt的庚烷脱氢环化制甲苯的粒径关系等,以及相关模型催化研究技术的进展。     

CO Extrusion in Homogeneous Gold Catalysis: Reactivity of Gold Acyl Species Generated through Water Addition to Gold Vinylidenes

Herein, we describe a new gold‐catalyzed decarbonylative indene synthesis. Synergistic σ,π‐activation of diyne substrates leads to gold vinylidene intermediates, which upon addition of water are transformed into gold acyl species, a type of organogold compound hitherto only scarcely reported. The latter are shown to undergo extrusion of CO, an elementary step completely unknown for homogeneous gold catalysis. By tuning the electronic and steric properties of the starting diyne systems, this new reactivity could be exploited for the synthesis of indene derivatives in high yields.     

Metal–Support Cooperative Catalysts for Environmentally Benign Molecular Transformations

Metal–support cooperative catalysts have been developed for sustainable and environmentally benign molecular transformations. The active metal centers and supports in these catalysts could cooperatively activate substrates, resulting in high catalytic performance for liquid‐phase reactions under mild conditions. These catalysts involved hydrotalcite‐supported gold and silver nanoparticles with high catalytic activity for organic reactions such as aerobic oxidation, oxidative carbonylation, and chemoselective reduction of epoxides to alkenes and nitrostyrenes to aminostyrenes using alcohols and CO/H₂O as reducing reagents. This high catalytic performance was due to cooperative catalysis between the metal nanoparticles and basic sites of the hydrotalcite support. To increase the metal–support cooperative effect, core–shell nanostructured catalysts consisting of gold or silver nanoparticles in the core and ceria supports in the shell were designed. These core–shell nanocomposite catalysts were effective for the chemoselective hydrogenation of nitrostyrenes to aminostyrenes, unsaturated aldehydes to allyl alcohols, and alkynes to alkenes using H₂ as a clean reductant. In addition, these solid catalysts could be recovered easily from the reaction mixture by simple filtration, and were reusable with high catalytic activity.     

金/钯双金属纳米颗粒协同催化酰胺和醇间氢自转移反应中路易斯酸驱动反应路径

金属纳米颗粒,特别是金和它的双金属纳米颗粒作为强大的绿色催化剂广泛用于有机合成反应中。在一个反应体系中使用2个不同催化剂(如协同催化),在均相催化中是一个很好的策略。然而,这种方法仍在发展中。最近我们发现,金/钯双金属纳米颗粒与路易斯酸的协同催化体系可用于伯胺的N-烷基化：即酰胺与醇之间的氢自转移反应。我们详细报道了路易斯酸对该氢自转移反应的影响。结果表明,所选的路易斯酸不仅影响生成目标产物的反应路径,而且影响生成多个中间体和副产物的反应路径。弱的路易斯酸,如三氟甲磺酸碱土金属盐,非常适合酰胺的N-烷基化反应。