Flow Rhodaelectro-Catalyzed Alkyne Annulations by Versatile C-H Activation: Mechanistic Support for Rhodium(III/IV)

Tunable Rh(III)-Catalyzed C(sp2)-H Bond Functionalization of Aryl Imidates with Cyclic 1,3-Diones: Strategic Use of Directing Groups

A tunable Rh(III)-catalyzed C(sp2)-H bond functionalization of aryl imidates with cyclic 1,3-diones was developed. With suitable and straightforward reaction condition adjustments, the C-H bond functionalization of diverse aryl imidates with cyclic 1,3-diones occurred smoothly and precisely at room temperature. Accompanied by different directing group transformations, a series of corresponding aryl nitriles, hydrophenanthridin-1(2H)-ones, spiro isoindoles, or hydrophenanthridine-1,6(2H,5H)-diones were synthesized in good yields to provide a rational directing group utilization strategy for the Rh(III)-catalyzed C(sp2)-H bond activation. Control experiments and primary mechanistic studies revealed that solvent effects and functional group electronic effects might influence the reaction's selectivity.

Revealing the Mechanistic Features of an Electrosynthetic Catalytic Reaction and the Role of Redox Mediators through DFT Calculations and Microkinetic Modeling

Organic electrosynthesis is an emerging field that provides original selectivity while adding features of atom economy, sustainability, and selectivity. Electrosynthesis is often enhanced by redox mediators or electroauxiliaries. The mechanistic understanding of organic electrosynthesis is however often limited by the low lifetime of intermediates and its difficult detection. In this work, we report a computational analysis of the mechanism of an appealing reaction previously reported by Mei and co-workers which is catalyzed by copper and employs iodide as redox mediator. Our scheme combines DFT calculations with microkinetic modeling and covers both the reaction in solution and the electrodic steps. A detailed mechanistic scheme is obtained which reproduces well experimental data and opens perspectives for the general treatment of these processes.

Ruthenium(II)-Catalyzed Oxidative Annulation of Imidazo[1,5-a]quinolin-2-iums Salts and Internal Alkynes via C-H Bond Activation

Ruthenium(II)-catalyzed synthesis of π-conjugated fused imidazo[1,5-a]quinolin-2-ium derivatives have been achieved via C-H activation of quinoline-functionalized NHC (NHC=N-heterocyclic carbene) and oxidative coupling with internal alkynes. The reaction occurred with high efficiency, broad substrate scope, tolerates a wide range of functional groups and utilized into a gram-scale. Synthetic applications of the coupled product have been exemplified in the late-stage derivatization of various highly functionalized scaffolds. Moreover, most of the annulated products exhibit intense fluorescence and have potential applications in optoelectronic devices. Mechanistic studies have provided insights into the spectroscopic characterization of key five-membered ruthenacycle intermediate and Ru(0) sandwich species. Based on several control experiments, deuterium-kinetic isotope effect, and thermodynamic activation parameters the mechanistic finding demonstrated that fused imidazo-[1,5-a]quinolin-2-ium C(2)-H bond cleavage is the rate-determining step and ruling out the possibility of reductive elimination for controlling the rate of reaction.

Electrochemical Enantioselective C-H Annulation by Achiral Rhodium(III)/Chiral Brønsted Base Domino Catalysis

Rhodium(III)-catalyzed enantioselective C-H activation has emerged as a powerful tool for assembling enabling chiral molecules. However, this approach is significantly hampered by the cumbersome synthetic routes for preparing chiral rhodium catalysts. In sharp contrast, we herein report on an electrochemical domino catalysis system that exploits an achiral Cp*-rhodium catalyst along with an easily accessible chiral Brønsted base for an enantioselective C-H activation/annulation reaction of alkenes by benzoic acids. Our strategy offers an environmentally benign and most user-friendly approach for assembling synthetically useful chiral phthalides in good enantioselectivity, employing electricity as the sustainable oxidant.

Green advancements towards the electrochemical synthesis of heterocycles

Heterocyclic chemistry is a large field with diverse applications in the areas of biological research and pharmaceutical advancement. Numerous initiatives have been proposed to further enhance the reaction conditions to reach these compounds without using harmful compounds. This paper focuses on the recent advances in the eco-friendly and green synthetic procedures to synthesize N-, S-, and O-heterocycles. This approach demonstrates considerable potential in accessing such compounds while circumventing the need for stoichiometric quantities of oxidizing/reducing agents or catalysts containing precious metals. Merely employing catalytic quantities of these substances proves sufficient, thereby offering an optimal means of contributing to resource efficiency. Renewable electricity plays a crucial role in generating environmentally friendly electrons (oxidant/reductant) that serve as catalysts for a series of reactions. These reactions involve the production of reactive intermediates, which in turn allow the synthesis of new chemical bonds, enabling beneficial transformations to occur. Furthermore, the utilization of metals as active catalysts in electrochemical activation has been recognized as an effective approach for achieving selective functionalization. The aim of this review was to summarize the electrochemical synthetic procedures so that the undesirable side reactions can be considerably reduced and the practical potential range of the chemical reactions can be expanded significantly.

Diversity-Oriented Synthesis of Indole-Fused Polycyclic Scaffolds via Rhodium-Catalyzed NH-Indole-Directed C-H Coupling of 2-Phenyl-1H-indoles with Propargylic Alcohol Derivatives

Diversity-oriented synthesis strategy for the efficient assembly of indole-fused polycyclic scaffolds via rhodium-catalyzed NH-indole-directed C-H coupling with propargylic alcohol derivatives in a regioselective manner was developed. Five 2-phenyl-1H-indole-embedded core skeletons were synthesized. In particular, three different indole-fused exo-olefin-containing polycycles were realized, which may be manipulated for further chemistry.

Electrooxidative Rhodium(III)/Chiral Carboxylic Acid-Catalyzed Enantioselective C-H Annulation of Sulfoximines with Alkynes

The combination of achiral Cp*Rh(III) with chiral carboxylic acids (CCAs) represents an efficient catalytic system in transition metal-catalyzed enantioselective C-H activation. However, this hybrid catalysis is limited to redox-neutral C-H activation reactions and the adopt to oxidative enantioselective C-H activation remains elusive and pose a significant challenge. Herein, we describe the development of an electrochemical Cp*Rh(III)-catalyzed enantioselective C-H annulation of sulfoximines with alkynes enabled by chiral carboxylic acid (CCA) in an operationally friendly undivided cell at room temperature. A broad range of enantioenriched 1,2-benzothiazines are obtained in high yields with excellent enantioselectivities (up to 99 % yield and 98 : 2 er). The practicality of this method is demonstrated by scale-up reaction in a batch reactor with external circulation. A crucial chiral Cp*Rh(III) intermediate is isolated, characterized, and transformed, providing rational support for a Rh(III)/Rh(I) electrocatalytic cycle.

Electrochemical Late-Stage Functionalization

Late-stage functionalization (LSF) constitutes a powerful strategy for the assembly or diversification of novel molecular entities with improved physicochemical or biological activities. LSF can thus greatly accelerate the development of medicinally relevant compounds, crop protecting agents, and functional materials. Electrochemical molecular synthesis has emerged as an environmentally friendly platform for the transformation of organic compounds. Over the past decade, electrochemical late-stage functionalization (eLSF) has gained major momentum, which is summarized herein up to February 2023.

Arenes and Heteroarenes C-H Functionalization Under Enabling Conditions: Electrochemistry, Photoelectrochemistry & Flow Technology

C-H bond functionalization generates molecular complexity in single-step transformation. However, the activation of C-H bonds requires expensive metals or stoichiometric amounts of oxidizing/reducing species. In many cases, they often require pre-functionalization of starting molecules. Such pre-activating measures cause waste generation and their separation from the final product is also troublesome. In such a scenario, reactions activating elements generating from renewable energy resources such as electricity and light would be more efficient, green, and cost-effective. Further, incorporation of growing flow technology in chemical transformation processes will accelerate the safer accesses of valuable products. Arenes & heteroarenes are ubiquitous in pharmaceuticals, natural products, medicinal compounds, and other biologically important molecules. Herein, we discussed enabling tools and technologies used for the recent C-H bonds functionalization of arenes and heteroarenes.

Bifurcated Rhodaelectro-catalyzed C-H Activation for the Synthesis of Pyrroles and Lactones

While electrocatalyzed alkyne annulations of arenes represent a powerful strategy for the assembly of heteroaromatic motives, electrochemical C(sp2)-H activations of alkenes remain scarce. Herein, a strategy for the rhodaelectro-catalyzed functionalization of enamides is presented for the efficient construction of pyrroles using electricity as a sustainable oxidant. Moreover, the tuning of the solvent system allowed a fascinating switch in chemoselectivity, which is not possible with traditionally used chemical oxidants, giving rise to lactone architectures. The rhoda-electrocatalysis features a broad scope as well as high regio- and chemoselectivities.

Electrochemical Syntheses of Polycyclic Aromatic Hydrocarbons (PAHs)

Polycyclic aromatic hydrocarbons (PAHs) have surfaced as increasingly viable components in optoelectronics and material sciences. The development of highly efficient and atom-economic tools to prepare PAHs under exceedingly mild conditions constitutes a long-term goal. Traditional syntheses of PAHs have largely relied on multistep approaches or the conventional Scholl reaction. However, Scholl reactions are largely inefficient with electron-deficient substrates, require stoichiometric chemical oxidants, and typically occur in the presence of strong acid. In sharp contrast, electrochemistry has gained considerable momentum during the past decade as an alternative for the facile and straightforward PAHs assembly, generally via electro-oxidative dehydrogenative annulation, releasing molecular hydrogen as the sole stoichiometric byproduct by the hydrogen evolution reaction. This review provides an overview on the recent and significant advances in the field of electrochemical syntheses of various PAHs until January 2023.

Transition Metal-Catalyzed C-H Functionalization Through Electrocatalysis

Electrochemically promoted transition metal-catalyzed C-H functionalization has emerged as a promising area of research over the last few decades. However, development in this field is still at an early stage compared to traditional functionalization reactions using chemical-based oxidizing agents. Recent reports have shown increased attention on electrochemically promoted metal-catalyzed C-H functionalization. From the standpoint of sustainability, environmental friendliness, and cost effectiveness, electrochemically promoted oxidation of a metal catalyst offers a mild, efficient, and atom-economical alternative to traditional chemical oxidants. This Review discusses advances in the field of transition metal-electrocatalyzed C-H functionalization over the past decade and describes how the unique features of electricity enable metal-catalyzed C-H functionalization in an economic and sustainable way.

Heterocyclic Electrochemistry: Renewable Electricity in the Construction of Heterocycles

Numerous applications in the realm of biological exploration and drug synthesis can be found in heterocyclic chemistry, which is a vast subject. Many efforts have been developed to further improve the reaction conditions to access this interesting family to prevent employing hazardous ingredients. In this instance, it has been stated that green and environmentally friendly manufacturing methodologies have been introduced to create N-, S-, and O-heterocycles. It appears to be one of the most promising methods to access these types of compounds avoiding use of stoichiometric amounts of oxidizing/reducing species or precious metal catalysts, in which only catalytic amounts are sufficient, and it represent an ideal way of contributing toward the resource economy. Thus, renewable electricity provides clean electrons (oxidant/reductant) that initiate a reaction cascade via producing reactive intermediates that facilitate in building new bonds for valuable chemical transformations. Moreover, electrochemical activation using metals as catalytic mediators has been identified as a more efficient strategy toward selective functionalization. Thus, indirect electrolysis makes the potential range more practical, and less side reactions can occur. The latest developments in using an electrolytic strategy to create N-, S-, and O-heterocycles are the main topic of this mini review, which was documented over the last five years.

Electrochemical organic reactions: A tutorial review

Although the core of electrochemistry involves simple oxidation and reduction reactions, it can be complicated in real electrochemical organic reactions. The principles used in electrochemical reactions have been derived using physical organic chemistry, which drives other organic/inorganic reactions. This review mainly comprises two themes: the first discusses the factors that help optimize an electrochemical reaction, including electrodes, supporting electrolytes, and electrochemical cell design, and the second outlines studies conducted in the field over a period of 10 years. Electrochemical reactions can be used as a versatile tool for synthetically important reactions by modifying the constant electrolysis current.

Cobalt-electrocatalytic C-H hydroxyalkylation of N-heteroarenes with trifluoromethyl ketones

Trifluoromethyl carbinols and N-heteroarenes are both prevalent in bioactive molecules. However, access to high-value pharmacophores combining these two functional groups still remains a challenge. Herein, we report an electro-chemical redox-neutral coupling for the synthesis of N-heteroaryl trifluoromethyl carbinols from readily available N-heteroarenes and trifluoromethyl ketones. The reaction starts with reversing the polarity of ketones to nucleophilic ketyl radicals through an electrocatalytic proton-coupled electron transfer (PCET), followed by radical addition to heteroarenes and rearomatization to afford tertiary alcohol products. Importantly, the merging of paired electrolysis and cobalt catalysis is crucial to this regioselective C-H hydroxyalkylation of heteroarenes, and thus avoids several known competing pathways including the spin-center shift (SCS) process. Collectively, this protocol provides straightforward access to heteroaryl trifluoromethyl carbinols, featuring ideal atom economy, excellent regioselectivity, and paired redox-neutral electrolysis.

Silver-Free C-H Activation: Strategic Approaches towards Realizing the Full Potential of C-H Activation in Sustainable Organic Synthesis

The activation of carbon-hydrogen bonds is considered as one of the most attractive techniques in synthetic organic chemistry because it bears the potential to shorten synthetic routes as well as to produce complementary product scopes compared to traditional synthetic strategies. However, many current methods employ silver salts as additives, leading to stoichiometric metal waste and thereby preventing the full potential of C-H activation to be exploited. Therefore, the development of silver-free protocols has recently received increasing attention. Mechanistically, silver can serve various roles in C-H activation and thus, avoiding the use of silver requires different approaches based on the role it serves in a given process. In this Review, we present the comparison of silver-based and silver-free methods. Focusing on the strategic approaches to develop silver-free C-H activation, we provide the reader with the means to develop sustainable methods for C-H activation.

Sulfilimines as Transformable and Retainable Directing Groups in Rhodium-Catalyzed ortho-C-H Bond Functionalization

Shown herein is the first time that the sulfilimine is utilized as a directing group for Rh(III)-catalyzed C-H activation/annulation with intermolecular and intramolecular alkyne compounds. Sulfilimine serves as a transformable directing group, an internal oxidant, in the annulation with an alkyne moiety via N-S bond cleavage. Notably, the retention of sulfilimine as a directing group is also achieved in the Rh(III)-catalyzed ortho-alkynylation with alkyne bromides.

Electricity Induced Rhodium-Catalyzed Oxidative C-H/N-H Annulation of Alkynes with Arylhydrophthalazinediones

The development of stoichiometric oxidant-free regioselective annulation protocol is a challenging aspect in organic synthesis. Herein, we disclose electricity as a greener oxidant for the C-H/N-H annulation to construct cinnolines using rhodium(III) catalyst under mild conditions. A detailed mechanistic investigation revealed the possibility of both Rh(III/I) and Rh(III/IV) catalytic cycles for the formation of annulated product. Exclusive regioselectivity, diverse substrate scope, and commercially available cheap graphite electrodes are key features of this protocol.

Rhodaelectro-Catalyzed peri-Selective Direct Alkenylations with Weak O-Coordination Enabled by the Hydrogen Evolution Reaction (HER)

Direct C-H functionalizations by electrocatalysis is dominated by strongly coordinating N(sp2 )-directing groups. In sharp contrast, direct electrocatalytic transformations of weakly-coordinating phenols remain underdeveloped. Herein, electrooxidative peri C-H alkenylations of challenging 1-naphthols were achieved by versatile rhodium(III) catalysis via user-friendly constant current electrolysis. The rhodaelectrocatalysis employed readily-available alkenes and a protic reaction medium and features ample scope, good functional group tolerance and high site- and stereoselectivity. The strategy was successfully applied to high-value, nitrogen-containing heterocycles, thereby providing direct access to uncommon heterocyclic motifs based on the dihydropyranoquinoline skeleton.

Distal Ruthenaelectro-Catalyzed meta-C-H Bromination with Aqueous HBr

While electrochemical ortho-selective C-H activations are well established, distal C-H activations continue to be underdeveloped. In contrast, we herein describe the electrochemical meta-C-H functionalization. The remote C-H bromination was accomplished in an undivided cell by RuCl3 ⋅3 H2 O with aqueous HBr. The electrohalogenation proceeded under exogenous ligand- and electrolyte-free conditions. Notably, pyrazolylarenes were meta-selectively brominated at the benzenoid moiety, rather than on the electron-rich pyrazole ring for the first time. Mechanistic studies were suggestive of an initial ruthenacycle formation, and a subsequent ligand-to-ligand hydrogen transfer (LLHT) process to liberate the brominated product.

C-H Bond Functionalization under Electrochemical Flow Conditions

Electrochemical C-H functionalization is a rapidly growing area of interest in organic synthesis. To achieve maximum atom economy, the flow electrolysis process is more sustainable. This allows shorter reaction times, safer working environments, and better selectivities. Using this technology, the problem of overoxidation can be reduced and less emergence of side products or no side products are possible. Flow electro-reactors provide high surface-to-volume ratios and contain electrodes that are closely spaced where the diffusion layers overlap to give the desired product, electrochemical processes can now be managed without the need for a deliberately added supporting electrolyte. Considering the importance of flow electrochemical C-H functionalization, a comprehensive review is presented. Herein, we summarize flow electrolysis for the construction of C-C and C-X (X=O, N, S, and I) bonds formation. Also, benzylic oxidation and access to biologically active molecules are discussed.

Advances on the Merger of Electrochemistry and Transition Metal Catalysis for Organic Synthesis

Synthetic organic electrosynthesis has grown in the past few decades by achieving many valuable transformations for synthetic chemists. Although electrocatalysis has been popular for improving selectivity and efficiency in a wide variety of energy-related applications, in the last two decades, there has been much interest in electrocatalysis to develop conceptually novel transformations, selective functionalization, and sustainable reactions. This review discusses recent advances in the combination of electrochemistry and homogeneous transition-metal catalysis for organic synthesis. The enabling transformations, synthetic applications, and mechanistic studies are presented alongside advantages as well as future directions to address the challenges of metal-catalyzed electrosynthesis.

Technological Innovations in Photochemistry for Organic Synthesis: Flow Chemistry, High-Throughput Experimentation, Scale-up, and Photoelectrochemistry

Photoinduced chemical transformations have received in recent years a tremendous amount of attention, providing a plethora of opportunities to synthetic organic chemists. However, performing a photochemical transformation can be quite a challenge because of various issues related to the delivery of photons. These challenges have barred the widespread adoption of photochemical steps in the chemical industry. However, in the past decade, several technological innovations have led to more reproducible, selective, and scalable photoinduced reactions. Herein, we provide a comprehensive overview of these exciting technological advances, including flow chemistry, high-throughput experimentation, reactor design and scale-up, and the combination of photo- and electro-chemistry.

A Strategy for Site- and Chemoselective C-H Alkenylation through Osmaelectrooxidative Catalysis

Herein, we disclose osmaelectrocatalyzed C-H activations that set the stage for electrooxidative alkyne annulations by benzoic acids. The osmium electrocatalysis enables site- and chemoselective electrooxidative C-H activations with unique levels of selectivity. The isolation of unprecedented osmium(0) and osmium(II) intermediates, along with crystallographic characterization and analyses by spectrometric and spectroscopic in operando techniques delineate a synergistic osmium redox catalyst regime. Detailed mechanistic studies revealed a facile C-H cleavage, which allows for an ample substrate scope, providing provide robust and user-friendly access to annulated heterocycles.

Rhodium(III)-Catalyzed Cascade Reactions of Imines/Imidates with 4-Hydroxy-2-alkynoates to Synthesize Regioselective Furanone-Fused Isoquinoline Scaffolds

A regioselective synthesis of furanone-fused isoquinoline heterocycles is developed in a single step using a Rh(III) catalyst. In this reaction, a cascade C-H activation, regioselective annulation, and lactonization occur in one pot. A wide range of alkynoates was examined, which showed good regioselectivity. The regioselectivity was guided by steric bulk at the C4 position of the 4-hydroxy-2-alkynoates. The synthetic utility was exemplified, and the model reaction was scaled up to a 1 g scale.

Electrocatalytic C(sp3)-H/C(sp)-H cross-coupling in continuous flow through TEMPO/copper relay catalysis

Electrocatalytic dehydrogenative C(sp3)-H/C(sp)-H cross-coupling of tetrahydroisoquinolines with terminal alkynes has been achieved in a continuous-flow microreactor through 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO)/copper relay catalysis. The reaction is easily scalable and requires low concentration of supporting electrolyte and no external chemical oxidants or ligands, providing straightforward and sustainable access to 2-functionalized tetrahydroisoquinolines.

Rhodium(III)-Catalyzed [4 + 2] Annulation of N-Arylbenzamidines with Propargyl Alcohols: Highly Regioselective Synthesis of 1-Aminoisoquinolines Controlled by Noncovalent Interaction

A highly regioselective synthesis of 1-aminoisoquinolines has been explored via rhodium(III)-catalyzed C-H bond activation/annulation reactions of propargyl alcohols with N-arylbenzamidines. The imidamide was used as the directing group and the nitrogen source of the heterocycle and for regulating the regioselective migratory insertion of propargyl alcohol through a hydrogen bond. In this transformation, a specific isomer was obtained that would provide a new strategy for the synthesis of 1-aminoisoquinolines with biological activity.

Multiple Reaction Pathways of Eight-Membered Rhodacycles in Rh-Catalyzed Annulations of 2-Alkenyl Phenols/Anilides with Alkynes

Density functional theory calculations were performed to study the competing pathways of rhodacycle intermediates generated in Rh(III)-catalyzed annulations of 2-alkenyl phenols and 2-alkenyl anilides with alkynes. The results show that the multiple pathways of eight-membered rhodacycles can be subtly tuned to give specific cyclic products. The seven-membered oxacyclic and spirocyclic products from 2-alkenyl phenols are formed by favoring the pathway of dissociating the Rh-O bond of O-contained rhodacycles, which are followed by antarafacial nucleophilic attack. The indoline product from 2-alkenyl anilides is generated through the pathway of intramolecular olefin migratory insertion of the N-contained rhodacycle.

Rhodaelectro-catalyzed access to chromones via formyl C-H activation towards peptide electro-labeling

Chromones represent a privileged scaffold in medicinal chemistry and are an omnipresent structural motif in natural products. Chemically encoded non-natural peptidomimetics feature improved stability towards enzymatic degradation, cell permeability and binding affinity, translating into a considerable impact on pharmaceutical industry. Herein, a strategy for the sustainable assembly of chromones via electro-formyl C–H activation is presented. The rational design of the rhodaelectro-catalysis is guided by detailed mechanistic insights and provides versatile access to tyrosine-based fluorogenic peptidomimetics.

The chromone scaffold is present in drugs and bioactive natural products, but conventional approaches to access chromones require stoichiometric amounts of oxidants. Here, the authors report rhodaelectro-catalyzed assembly of chromones by electrochemical formyl C–H activations, providing the basis for late-stage peptide diversification.

Synthesis of 1-Benzyl-, 1-Alkoxyl-, and 1-Aminoisoquinolines via Rhodium(III)-Catalyzed Aryl C-H Activation and Alkyne Annulation

One-pot syntheses of 1-benzyl-, 1-alkoxyl-, and 1-alkylamino- isoquinolines through automatic directing group (DG^auto)-assisted, rhodium(III)-catalyzed aryl C-H activation and annulation with internal alkynes were developed. The reactions affording 1-benzylisoquinolines involve a cascade oximation of diarylacetylenes with hydroxylamine, forming aryl benzyl ketone oxime, and oxime-assisted rhodium(III)-catalyzed aryl C-H activation and followed annulation with another molecule of diarylacetylene in a one-pot manner. The formation of 1-alkoxyl/amino isoquinolines includes the addition of nucleophilic alcohols or amines to aryl nitriles, imine-assisted rhodium-catalyzed aryl C-H activation, and subsequent alkyne annulation.

Electrochemical activation of C-H by electron-deficient W2C nanocrystals for simultaneous alkoxylation and hydrogen evolution

The activation of C-H bonds is a central challenge in organic chemistry and usually a key step for the retro-synthesis of functional natural products due to the high chemical stability of C-H bonds. Electrochemical methods are a powerful alternative for C-H activation, but this approach usually requires high overpotential and homogeneous mediators. Here, we design electron-deficient W2C nanocrystal-based electrodes to boost the heterogeneous activation of C-H bonds under mild conditions via an additive-free, purely heterogeneous electrocatalytic strategy. The electron density of W2C nanocrystals is tuned by constructing Schottky heterojunctions with nitrogen-doped carbon support to facilitate the preadsorption and activation of benzylic C-H bonds of ethylbenzene on the W2C surface, enabling a high turnover frequency (18.8 h-1) at a comparably low work potential (2 V versus SCE). The pronounced electron deficiency of the W2C nanocatalysts substantially facilitates the direct deprotonation process to ensure electrode durability without self-oxidation. The efficient oxidation process also boosts the balancing hydrogen production from as-formed protons on the cathode by a factor of 10 compared to an inert reference electrode. The whole process meets the requirements of atomic economy and electric energy utilization in terms of sustainable chemical synthesis.

Evolution of Earth-Abundant 3 d-Metallaelectro-Catalyzed C-H Activation: From Chelation-Assistance to C-H Functionalization without Directing Groups

Catalyzed C-H functionalizations have emerged as a transformative platform for molecular syntheses. Despite of indisputable advances, oxidative C-H activations have been largely restricted to precious transition metals and stoichiometric amounts of chemical oxidants. In contrast, we herein discuss the potential of earth-abundant, environmentally-benign 3d transition metals for C-H activation, which has recently gained major momentum. Thus, a strategy for full resource economy has been established in our group, with green electricity as a renewable redox agent, giving valuable hydrogen as the sole byproduct under redox mediator-free conditions. In this account, we detail our accomplishments in 3d metallaelectrocatalysis towards green syntheses until March 2021.

Rhodaelectro-catalyzed chemo-divergent C-H activations with alkylidenecyclopropanes for selective cyclopropylations

Herein, we report on selectivity control in C-H activations with alkylidenecyclopropanes (ACPs) for the chemo-selective assembly of cyclopropanes or dienes. Thus, unprecedented rhodaelectro-catalyzed C-H activations were realized with diversely decorated ACPs with a wide substrate scope and electricity as the sole oxidant.

Single-Atom Catalysts: A Sustainable Pathway for the Advanced Catalytic Applications

A heterogeneous catalyst is a backbone of modern sustainable green industries; and understanding the relationship between its structure and properties is the key for its advancement. Recently, many upscaling synthesis strategies for the development of a variety of respectable control atomically precise heterogeneous catalysts are reported and explored for various important applications in catalysis for energy and environmental remediation. Precise atomic-scale control of catalysts has allowed to significantly increase activity, selectivity, and in some cases stability. This approach has proved to be relevant in various energy and environmental related technologies such as fuel cell, chemical reactors for organic synthesis, and environmental remediation. Therefore, this review aims to critically analyze the recent progress on single-atom catalysts (SACs) application in oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, and chemical and/or electrochemical organic transformations. Finally, opportunities that may open up in the future are summarized, along with suggesting new applications for possible exploitation of SACs.

Organic Electrochemistry: Molecular Syntheses with Potential

Efficient and selective molecular syntheses are paramount to inter alia biomolecular chemistry and material sciences as well as for practitioners in chemical, agrochemical, and pharmaceutical industries. Organic electrosynthesis has undergone a considerable renaissance and has thus in recent years emerged as an increasingly viable platform for the sustainable molecular assembly. In stark contrast to early strategies by innate reactivity, electrochemistry was recently merged with modern concepts of organic synthesis, such as transition-metal-catalyzed transformations for inter alia C-H functionalization and asymmetric catalysis. Herein, we highlight the unique potential of organic electrosynthesis for sustainable synthesis and catalysis, showcasing key aspects of exceptional selectivities, the synergism with photocatalysis, or dual electrocatalysis, and novel mechanisms in metallaelectrocatalysis until February of 2021.

Electrooxidative Rhodium-Catalyzed [5+2] Annulations via C-H/O-H Activations

Electrooxidative annulations involving mild transition metal-catalyzed C-H activation have emerged as a transformative strategy for the rapid construction of five- and six-membered heterocycles. In contrast, we herein describe the first electrochemical metal-catalyzed [5+2] cycloadditions to assemble valuable seven-membered benzoxepine skeletons by C-H/O-H activation. The efficient alkyne annulation featured ample substrate scope, using electricity as the only oxidant. Mechanistic studies provided strong support for a rhodium(III/I) regime, involving a benzoxepine-coordinated rhodium(I) sandwich complex as the catalyst resting state, which was re-oxidized to rhodium(III) by anodic oxidation.