Designed Nanomaterials for Electrocatalytic Organic Hydrogenation Using Water as the Hydrogen Source

Electrochemical C-H deuteration of pyridine derivatives with D2O

Herein, we develop a straightforward, metal-free, and acid-/base-free electrochemical C4-selective C - H deuteration of pyridine derivatives with economic and convenient D2O at room temperature. This strategy features an efficient and environmentally friendly approach with high chemo- and regioselectivity, affording a wide range of D-compounds, such as pyridines, quinolones, N-ligands and biorelevant compounds. Notably, the mechanistic experiments and cyclic voltammetry (CV) studies demonstrate that N-butyl-2-phenylpyridinium iodide is a crucial intermediate during the electrochemical transformation, which provides a general and efficient way for deuteration of pyridine derivatives.

Single-Atom Iron Catalyst as an Advanced Redox Mediator for Anodic Oxidation of Organic Electrosynthesis

Homogeneous electrocatalysts can indirect oxidate the high overpotential substrates through single-electron transfer on the electrode surface, enabling efficient operation of organic electrosynthesis catalytic cycles. However, the problems of this chemistry still exist such as high dosage, difficult recovery, and low catalytic efficiency. Single-atom catalysts (SACs) exhibit high atom utilization and excellent catalytic activity, hold great promise in addressing the limitations of homogeneous catalysts. In view of this, we have employed Fe-SA@NC as an advanced redox mediator to try to change this situation. Fe-SA@NC was synthesized using an encapsulation-pyrolysis method, and it demonstrated remarkable performance as a redox mediator in a range of reported organic electrosynthesis reactions, and enabling the construction of various C-C/C-X bonds. Moreover, Fe-SA@NC demonstrated a great potential in exploring new synthetic method for organic electrosynthesis. We employed it to develop a new electro-oxidative ring-opening transformation of cyclopropyl amides. In this new reaction system, Fe-SA@NC showed good tolerance to drug molecules with complex structures, as well as enabling flow electrochemical syntheses and gram-scale transformations. This work highlights the great potential of SACs in organic electrosynthesis, thereby opening a new avenue in synthetic chemistry.

Tandem Electrocatalytic Alkyne Semihydrogenation over Bicomponent Catalysts through Hydrogen Spillover

Electrocatalytic alkyne semihydrogenation under mild conditions is a more attractive approach for alkene production than industrial routes but suffers from either low production efficiency or high energy consumption. Here, we describe a tandem catalytic concept that overcomes these challenges. Component (i), which can trap hydrogen effectively, is partnered with component (ii), which can readily release hydrogen for hydrogenation, to enable efficient generation of active hydrogen on component (i) at low overpotentials and timely (i)-to-(ii) hydrogen spillover and facile desorptive hydrogenation on component (ii). We examine this concept over bicomponent palladium-copper catalysts for the production of representative 2-methyl-3-butene-2-ol (MBE) from 2-methyl-3-butyne-2-ol (MBY) and achieve a record high MBE production rate of 1.44 mmol h-1 cm-2 and a Faraday efficiency of ~88.8 % at a low energy consumption of 1.26 kWh kgMBE -1. With these catalysts, we further achieve 60 h continuous production of MBE with record high profit space.

Electrochemical hydrogenation and oxidation of organic species involving water

Fossil fuel-driven thermochemical hydrogenation and oxidation using high-pressure H2 and O2 are still popular but energy-intensive CO2-emitting processes. At present, developing renewable energy-powered electrochemical technologies, especially those using clean, safe and easy-to-handle reducing agents and oxidants for organic hydrogenation and oxidation reactions, is urgently needed. Water is an ideal carrier of hydrogen and oxygen. Electrochemistry provides a powerful route to drive water splitting under ambient conditions. Thus, electrochemical hydrogenation and oxidation transformations involving water as the hydrogen source and oxidant, respectively, have been developed to be mild and efficient tools to synthesize organic hydrogenated and oxidized products. In this Review, we highlight the advances in water-participating electrochemical hydrogenation and oxidation reactions of representative organic molecules. Typical electrode materials, performance metrics and key characterization techniques are firstly introduced. General electrocatalyst design principles and controlling the microenvironment for promoting hydrogenation and oxygenation reactions involving water are summarized. Furthermore, paired hydrogenation and oxidation reactions are briefly introduced before finally discussing the challenges and future opportunities of this research field.

Electroreduction of unactivated alkenes using water as hydrogen source

Herein, we report an electroreduction of unactivated alkyl alkenes enabled by [Fe]-H, which is provided through the combination of anodic iron salts and the silane generated in situ via cathodic reduction, using H2O as an H-source. The catalytic amounts of Si-additive work as an H-carrier from H2O to generate a highly active silane species in situ under continuous electrochemical conditions. This approach shows a broad substrate scope and good functional group compatibility. In addition to hydrogenation, the use of D2O instead of H2O provides the desired deuterated products in good yields with excellent D-incorporation (up to >99%). Further late-stage hydrogenation of complex molecules and drug derivatives demonstrate potential application in the pharmaceutical industry. Mechanistic studies are performed and provide support for the proposed mechanistic pathway.

Synergistic enhancement of electrocatalytic nitroarene hydrogenation over Mo2C@MoS2 heteronanorods with dual active-sites

Electrocatalytic hydrogenation (ECH) enables the sustainable production of chemicals under ambient conditions, in which catalysts catering for the different chemisorption of reactants/intermediates are desired but still challenging. Here, Mo2C@MoS2 heteronanorods with dual active-sites are developed to accomplish efficient nitroarene ECH according to our theoretical prediction that the binding of atomic H and nitro substrates would be synergistically strengthened on Mo2C-MoS2 interfaces. They afford high faradaic efficiency (>85%), yield (>78%) and selectivity (>99%) for the reduction of 4-nitrostyrene (4-NS) to 4-vinylaniline (4-VA) in neutral electrolytes, outperforming not only the single-component counterparts of Mo2C nanorods and MoS2 nanosheets, but also recently reported noble-metals. Accordingly, in situ Raman spectroscopy combined with electrochemical tests clarifies the rapid ECH of 4-NS on Mo2C-MoS2 interfaces due to the facilitated elementary steps, quickly refreshing active sites for continuous electrocatalysis. Mo2C@MoS2 further confirms efficient and selective ECH toward functional anilines with other well-retained reducible groups in wide substrate scope, underscoring the promise of dual-site engineering for exploring catalysts.

Electrocatalytic Hydrogenation Using Palladium Membrane Reactors

Hydrogenation is a crucial chemical process employed in a myriad of industries, often facilitated by metals such as Pd, Pt, and Ni as catalysts. Traditional thermocatalytic hydrogenation usually necessitates high temperature and elevated pressure, making the process energy intensive. Electrocatalytic hydrogenation offers an alternative but suffers from issues such as competing H2 evolution, electrolyte separation, and limited solvent selection. This Perspective introduces the evolution and advantages of the electrocatalytic Pd membrane reactor (ePMR) as a solution to these challenges. ePMR utilizes a Pd membrane to physically separate the electrochemical chamber from the hydrogenation chamber, permitting the use of water as the hydrogen source and eliminating the need for H2 gas. This setup allows for greater control over reaction conditions, such as solvent and electrolyte selection, while mitigating issues such as low Faradaic efficiency and complex product separation. Several representative hydrogenation reactions (e.g., hydrogenation of C=C, C≡C, C=O, C≡N, and O=O bonds) achieved via ePMR over the past 30 years were concisely discussed to highlight the unique advantages of ePMR. Promising research directions along with the advancement of ePMR for more challenging hydrogenation reactions are also proposed. Finally, we provide a prospect for future development of this distinctive hydrogenation strategy using hydrogen-permeable membrane electrodes.

Alkynes Electrooxidation to α,α-Dichloroketones in Seawater with Natural Chlorine Participation via Competitive Reaction Inhibition and Tip-Enhanced Reagent Concentration

The traditional synthesis of α,α-dichloroketones usually requires corrosive chlorine, harsh reaction conditions, or excessive electrolytes. Here, we report an electrooxidation strategy of ethynylbenzenes to α,α-dichloroketones by directly utilizing seawater as the chlorine source and electrolyte solution without an additional supporting electrolyte. High-curvature NiCo2O4 nanocones are designed to inhibit competitive O2 and Cl2 evolution reactions and concentrate Cl- and OH- ions, accelerating α,α-dichloroketone electrosynthesis. NiCo2O4 nanocones produce 81% yield, 61% Faradaic efficiency, and 44.2 mmol gcat.-1 h-1 yield rate of α,α-dichloroketones, outperforming NiCo2O4 nanosheets. A Cl• radical triggered Cl• and OH• radical addition mechanism is revealed by a variety of radical-trapping and control experiments. The feasibility of a solar-powered electrosynthesis system, methodological universality, and extended synthesis of α,α-dichloroketone-drug blocks confirm its practical potential. This work may provide a sustainable solution to the electrocatalytic synthesis of α,α-dichloroketones via the utilization of seawater resources.

Single-Atom Manganese-Catalyzed Oxygen Evolution Drives the Electrochemical Oxidation of Silane to Silanol

The oxygen evolution reaction (OER), characterized by a four-electron transfer kinetic process, represents a significant bottleneck in improving the efficiency of hydrogen production from water electrolysis. Consequently, extensive research efforts have been directed towards identifying single-atom electrocatalysts with exceptional OER performance. Despite the comprehensive understanding of the OER mechanism, its application to other valuable synthetic reactions has been limited. Herein, we leverage the MOOH intermediate, a key species in the Mn-N-C single-atom catalyst (Mn-SA@NC), which can be cyclically delivered in the OER. We exploit this intermediate' s capability to facilitate electrophilic transfer with silane, enabling efficient silane oxidation under electrochemical conditions. The SAC electrocatalytic system exhibits remarkable performance with catalyst loadings as low as 600 ppm and an exceptional turnover number of 9132. Furthermore, the catalytic method demonstrates stability under a 10 mmol flow chemistry setup. By serving as an OER electrocatalyst, the Mn-SA@NC drives the entire reaction, establishing a practical Mn SAC-catalyzed organic electrosynthesis system. This synthesis approach not only presents a promising avenue for the utilization of electrocatalytic OER but also highlights the potential of SACs as an attractive platform for organic electrosynthesis investigations.

Insight into the Change in Local pH near the Electrode Surface Using Phosphate Species as the Probe

The difference between solution pH and local pH near an electrode surface greatly determines the electrocatalytic performance. However, there is still a lack of a facile and universal method for the local pH detection of various electrode reactions, leaving the origin of local pH changes unclear. Herein, by using phosphate species in phosphate buffer solution (PBS) as the pH probe, we demonstrate a universal local pH detection strategy through in situ Raman spectroscopy for various electrode reactions. Oxygen evolution is chosen as the example to detect the potential-dependent local pH change. Then the strategy extends to nitrate reduction, nitrobenzene reduction, and benzylamine oxidation. By comparing the local pH changes in different reactions, we reveal that the local pH change is strongly dependent on the reaction current, the ability of the system to replenish the local H+/OH-, and the number of H+/OH- per electron transfer of the electrode reaction.

Organo-Mediator Enabled Electrochemical Deuteration of Styrenes

Despite widespread use of the deuterium isotope effect, selective deuterium labeling of chemical molecules remains a major challenge. Herein, a facile and general electrochemically driven, organic mediator enabled deuteration of styrenes with deuterium oxide (D2 O) as the economical deuterium source was reported. Importantly, this transformation could be suitable for various electron rich styrenes mediated by triphenylphosphine (TPP). The reaction proceeded under mild conditions without transition-metal catalysts, affording the desired products in good yields with excellent D-incorporation (D-inc, up to >99 %). Mechanistic investigations by means of isotope labeling experiments and cyclic voltammetry tests provided sufficient support for this transformation. Notably, this method proved to be a powerful tool for late-stage deuteration of biorelevant compounds.