Recent advances in transition metal-catalyzed asymmetric electrocatalysis

Recent advances in catalytic asymmetric synthesis

Asymmetric catalysis stands at the forefront of modern chemistry, serving as a cornerstone for the efficient creation of enantiopure chiral molecules characterized by their high selectivity. In this review, we delve into the realm of asymmetric catalytic reactions, which spans various methodologies, each contributing to the broader landscape of the enantioselective synthesis of chiral molecules. Transition metals play a central role as catalysts for a wide range of transformations with chiral ligands such as phosphines, N-heterocyclic carbenes (NHCs), etc., facilitating the formation of chiral C-C and C-X bonds, enabling precise control over stereochemistry. Enantioselective photocatalytic reactions leverage the power of light as a driving force for the synthesis of chiral molecules. Asymmetric electrocatalysis has emerged as a sustainable approach, being both atom-efficient and environmentally friendly, while offering a versatile toolkit for enantioselective reductions and oxidations. Biocatalysis relies on nature's most efficient catalysts, i.e., enzymes, to provide exquisite selectivity, as well as a high tolerance for diverse functional groups under mild conditions. Thus, enzymatic optical resolution, kinetic resolution and dynamic kinetic resolution have revolutionized the production of enantiopure compounds. Enantioselective organocatalysis uses metal-free organocatalysts, consisting of modular chiral phosphorus, sulfur and nitrogen components, facilitating remarkably efficient and diverse enantioselective transformations. Additionally, unlocking traditionally unreactive C-H bonds through selective functionalization has expanded the arsenal of catalytic asymmetric synthesis, enabling the efficient and atom-economical construction of enantiopure chiral molecules. Incorporating flow chemistry into asymmetric catalysis has been transformative, as continuous flow systems provide precise control over reaction conditions, enhancing the efficiency and facilitating optimization. Researchers are increasingly adopting hybrid approaches that combine multiple strategies synergistically to tackle complex synthetic challenges. This convergence holds great promise, propelling the field of asymmetric catalysis forward and facilitating the efficient construction of complex molecules in enantiopure form. As these methodologies evolve and complement one another, they push the boundaries of what can be accomplished in catalytic asymmetric synthesis, leading to the discovery of novel, highly selective transformations which may lead to groundbreaking applications across various industries.

Ionic liquid-assisted synthesis of N, F, and B co-doped BiOBr/Bi2Se3 on Mo2CTx for enhanced performance in hydrogen evolution reaction and supercapacitors

Heteroatom doping and heterojunction formation are effective strategies to enhance electrochemical performance. In this study, we present a novel approach that utilizes an ionic liquid-assisted synthesis method to fabricate a BiOBr-based material, which is subsequently loaded onto Mo2CTx via a selenization treatment to create a BiOBr/Bi2Se3 heterostructure, denoted as NBF-BiOBr/Bi2Se3/Mo2CTx. The incorporation of heteroatoms improves its hydrophilicity and electronegativity, while the formation of heterojunctions adjusts the electronic structure at the interface, resulting in lower OH-/H+ adsorption energy. The specific surface area of NBF-BiOBr/Bi2Se3/Mo2CTx is 193.1 m2/g. In hydrogen evolution reaction (HER) tests, NBF-BiOBr/Bi2Se3/Mo2CTx exhibits exceptional catalytic performance in acidic media, requiring only an overpotential of 109 mV to achieve a current density of 10 mA cm-2. Furthermore, NBF-BiOBr/Bi2Se3/Mo2CTx demonstrates superior electrochemical performance in an asymmetric supercapacitor, with an energy density as high as 55.6 Wh kg-1 at a power density of 749.9 Wh kg-1. This work provides a novel approach for heteroatom doping and heterojunction synthesis, offering promising prospects for further advancements in the field.

A tutorial on asymmetric electrocatalysis

Electrochemistry has emerged as a powerful means to enable redox transformations in modern chemical synthesis. This tutorial review delves into the unique advantages of electrochemistry in the context of asymmetric catalysis. While electrochemistry has historically been used as a green and mild alternative for established enantioselective transformations, in recent years asymmetric electrocatalysis has been increasingly employed in the discovery of novel asymmetric methodologies based on reaction mechanisms unique to electrochemistry. This tutorial review first provides a brief tutorial introduction to electrosynthesis, then explores case studies on homogenous small molecule asymmetric electrocatalysis. Each case study serves to highlight a key advance in the field, starting with the historic electrification of known asymmetric transformations and culminating with modern methods relying on unique electrochemical mechanistic sequences. Finally, we highlight case studies in the emerging reasearch areas at the interface of asymmetric electrocatalysis with biocatalysis and heterogeneous catalysis.

Indirect Electrocatalysis S─N/S─S Bond Construction by Robust Polyoxometalate Based Foams

Indirect electrocatalytic conversion of cheap organic raw materials via the activation of S─H and N─H bonds into the value-added S─N/S─S bonds chemicals for industrial rubber production is a promising strategy to realize the atomic economic reaction, during which the kinetic inhibition that is associated with the electron transfer at the electrode/electrolyte interface in traditional direct electrocatalysis can be eliminated to achieve higher performance. In this work, a series of di-copper-substituted phosphotungstatebased foams (PW10 Cu2 @CMC) are fabricated with tunable loadings (17 to 44 wt%), which can be successfully applied in indirect electrocatalytic syntheses of sulfenamides and disulfides. Specifically, the optimal PW10 Cu2 @CMC (44 wt%) exhibits excellent electrocatalytic performance for the construction of S─N/S─S bonds (yields up to 99%) coupling with the efficient production of H2 (≈50 µmol g-1  h-1 ). Remarkably, it enables the scale-up production (≈14.4 g in a batch experiment) and the obtained products can serve as rubber vulcanization accelerators with superior properties to traditional industrial rubber additives in real industrial processes. This powerful catalysis system that can simultaneously produce rubber vulcanization accelerator and H2 may inaugurate a new electrocatalytic avenue to explore polyoxometalate-based foam catalysts in electrocatalysis field.

Cobalt-catalyzed enantioselective intramolecular reductive cyclization via electrochemistry

Transition-metal catalyzed asymmetric cyclization of 1,6-enynes has emerged as a powerful method for the construction of carbocycles and heterocycles. However, very rare examples worked under electrochemical conditions. We report herein a Co-catalyzed enantioselective intramolecular reductive coupling of enynes via electrochemistry using H₂O as hydride source. The products were obtained in good yields with high regio- and enantioselectivities. It represents the rare progress on the cobalt-catalyzed enantioselective transformation via electrochemistry with a general substrate scope. DFT studies explored the possible reaction pathways and revealed that the oxidative cyclization of enynes by LCo(I) is more favorable than oxidative addition of H₂O or other pathways.

Electricity-driven asymmetric bromocyclization enabled by chiral phosphate anion phase-transfer catalysis

Electricity-driven asymmetric catalysis is an emerging powerful tool in organic synthesis. However, asymmetric induction so far has mainly relied on forming strong bonds with a chiral catalyst. Asymmetry induced by weak interactions with a chiral catalyst in an electrochemical medium remains challenging due to compatibility issues related to solvent polarity, electrolyte interference, etc. Enabled by a properly designed phase-transfer strategy, here we have achieved two efficient electricity-driven catalytic asymmetric bromocyclization processes induced by weak ion-pairing interaction. The combined use of a phase-transfer catalyst and a chiral phosphate catalyst, together with NaBr as the bromine source, constitutes the key advantages over the conventional chemical oxidation approach. Synergy over multiple events, including anodic oxidation, ion exchange, phase transfer, asymmetric bromination, and inhibition of Br₂ decomposition by NaHCO₃, proved critical to the success.

Counter Electrode Reactions-Important Stumbling Blocks on the Way to a Working Electro-organic Synthesis

Over the past two decades, electro-organic synthesis has gained significant interest, both in technical and academic research as well as in terms of applications. The omission of stoichiometric oxidizers or reducing agents enables a more sustainable route for redox reactions in organic chemistry. Even if it is well-known that every electrochemical oxidation is only viable with an associated reduction reaction and vice versa, the relevance of the counter reaction is often less addressed. In this Review, the importance of the corresponding counter reaction in electro-organic synthesis is highlighted and how it can affect the performance and selectivity of the electrolytic conversion. A selection of common strategies and unique concepts to tackle this issue are surveyed to provide a guide to select appropriate counter reactions for electro-organic synthesis.

Electrochemical Palladium‐Catalyzed Oxidative Carbonylation‐Cyclization of Enallenols

Herein, we report an electrochemical oxidative palladium-catalyzed carbonylation-carbocyclization of enallenols to afford γ-lactones and spirolactones, which proceeds with excellent chemoselectivity. Interestingly, electrocatalysis was found to have an accelerating effect on the rate of the tandem process, leading to a more efficient reaction than that under chemical redox conditions.

Facilitating Rh-Catalyzed C-H Alkylation of (Hetero)arenes and 6-Arylpurine Nucleosides (Nucleotides) with Electrochemistry

An electrochemical approach to promote the ortho-C-H alkylation of (hetero)arenes via rhodium catalysis under mild conditions is described. This approach features mild conditions with high levels of regio- and monoselectivity that tolerate a variety of aromatic and heteroaromatic groups and offers a widely applicable method for late-stage diversification of complex molecular architectures including tryptophan, estrone, diazepam, nucleosides, and nucleotides. Alkyl boronic acids and esters and alkyl trifluoroborates are demonstrated as suitable coupling partners. The isolation of key rhodium intermediates and mechanistic studies provided strong support for a rhodium(III/IV or V) regime.

Recent advances in transition-metal catalyzed directed C–H functionalization with fluorinated building blocks

This review focuses on the advances in transition-metal catalyzed reactions with fluorinated building blocks via directed C–H bond activation for the construction of diverse organic molecules with an insight into the probable mechanistic pathway.

Recent advances in organic electrosynthesis employing transition metal complexes as electrocatalysts

Organic electrosynthesis has been widely used as an environmentally conscious alternative to conventional methods for redox reactions because it utilizes electric current as a traceless redox agent instead of chemical redox agents. Indirect electrolysis employing a redox catalyst has received tremendous attention, since it provides various advantages compared to direct electrolysis. With indirect electrolysis, overpotential of electron transfer can be avoided, which is inherently milder, thus wide functional group tolerance can be achieved. Additionally, chemoselectivity, regioselectivity, and stereoselectivity can be tuned by the redox catalysts used in indirect electrolysis. Furthermore, electrode passivation can be avoided by preventing the formation of polymer films on the electrode surface. Common redox catalysts include N-oxyl radicals, hypervalent iodine species, halides, amines, benzoquinones (such as DDQ and tetrachlorobenzoquinone), and transition metals. In recent years, great progress has been made in the field of indirect organic electrosynthesis using transition metals as redox catalysts for reaction classes including C-H functionalization, radical cyclization, and cross-coupling of aryl halides-each owing to the diverse reactivity and accessible oxidation states of transition metals. Although various reviews of organic electrosynthesis are available, there is a lack of articles that focus on recent research progress in the area of indirect electrolysis using transition metals, which is the impetus for this review.