Pairing of Aqueous and Nonaqueous Electrosynthetic Reactions Enabled by a Redox Reservoir Electrode

A General Strategy for C(sp3)─H Bond Etherification via Quinoline Derivative-Mediated Electrolysis

Electrooxidative coupling of C(sp3)─H bonds with nucleophiles offers an attractive method for constructing C─C and C─X bonds without sacrificial oxidants. However, the direct electrochemical approach requires the nucleophilic reagent to have a higher potential than the C(sp3)─H coupling partners, which restricts the substrate scope. In this study, a quinoline derivative is introduced as an electrochemical mediator, enabling efficient C─H bond etherification with reduced reliance on the electronic properties of substrates. The catalytic system demonstrates broad substrate compatibility, extending to C(sp3)─H coupling partners featuring a diverse range of C─H bonds, including tertiary benzylic C─H bonds and unactivated C(sp3)─H bonds. Mechanistic investigations confirm the role of the electrocatalyst in the hydrogen atom transfer (HAT) process. This method provides a versatile and efficient strategy for the late-stage functionalization of bioactive molecules.

Efficient Alkaline-Free Electrooxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid using Electrochemically-Charged NixCo1-x(OH)2 as a Redox Mediator

Converting biomass-derived molecules like 5-hydroxymethylfurfural (HMF) into value-added products alongside hydrogen production using renewable energy offers significant opportunities for sustainable chemical and energy production. Yet, HMF electrooxidation requires strong alkaline conditions and membranes for efficient conversion. These harsh conditions destabilize HMF, leading to humin formation and reduced product purity, meanwhile membranes increase costs. Addressing these challenges, we introduce a two-step, decoupling system that operates without strong alkaline conditions and eliminates the need of membranes. In this system, nickel-cobalt hydroxides serve as effective redox mediators, driving HMF oxidation in pure water. The experimental results showed that Ni0.85Co0.15OOH effectively promotes the dehydrogenation of substrate and achieves a highly efficient oxidation of HMF in pure water, with the selectivity of product 2,5-furandicarboxylic acid (FDCA) approaching 100 %. This system has been expanded to oxidize various substrates, achieving yields exceeding 92 % for the corresponding acids of functionalized compounds such as furfuryl alcohol, furfural, benzyl alcohol, and benzaldehyde. By replacing fixed electrodes with flow electrodes, the scalability of decoupling strategy was evaluated for the harvesting of pure solid FDCA, highlighting the broad prospects in practical applications.

Regioselective Electrochemical Construction of Csp2-Csp2 Linkage at C5-C5' Position of 2-Oxindoles via an Intermolecular Anodic Dehydrogenative Coupling

Applying electricity as a reagent in synthetic organic chemistry has attracted particular attention from synthetic chemists worldwide as an environmentally benign and cost-effective technique. Herein, we report the construction of the Csp2-Csp2 linkage at the C5-C5' position of 2-oxindole utilizing electricity as the traceless oxidant in an anodic dehydrogenative homo-coupling process. A variety of 3,3-disubstituted-2-oxindoles were subjected to dimerization, achieving yields of up to 70 % through controlled potential electrolysis at an applied potential of 1.5 V versus Ag/Ag+ nonaqueous reference electrode. This electro-synthetic approach facilitates the specific assembly of C5-C5' (para-para coupled) dimer of 3,3-disubstituted-2-oxindole without the necessity of any external oxidants or additives and DFT (Density Functional Theory) calculations provided confirmation of this pronounced regioselectivity. Furthermore, validation through control experiments and voltammetric analyses substantiated the manifestation of radical-radical coupling (or biradical pathway) for the dimerization process.

Electrochemical Reductive Cross-Coupling of Alkyl or Alkenyl Halides with gem-Difluoroalkenes

Herein, we describe an electroreductive cross-electrophile coupling protocol for the construction of valuable monofluoroalkenes from easily accessible alkyl or alkenyl halides with gem-difluoroalkenes. The reaction can be conducted under sustainable and mild conditions delivering valuable and functionalized monofluoroalkenes with excellent Z-selectivity. The protocol's most notable advantage is the in situ release of nickel catalyst from the inexpensive electrodes without the addition of extra hazardous metal catalyst and superstoichiometric reductant.

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.

Recent Progress in Modular Electrochemical Synthesis of Hydrogen and High-Value-added Chemicals based on Solid Redox Mediator

Electrochemical synthesis of H2 and high-value-added chemicals is an efficient and cost-effective approach that can be powered using renewable electricity. Compared to a conventional electrochemical production system, the modular electrochemical production system (MEPS) based on a solid redox mediator (SRM) can separate the anodic and cathodic reactions in time and space. The MEPS can avoid the use of membranes and formation of useless products, as well as eliminate the mutual dependence of production rates at anode and cathode. The SRM can temporarily store or release electrons and ions to pair with cathodic and anodic reactions, respectively, in MEPS. Designing of SRMs with large charge capacity and good cyclability is of great significance for constructing a high-performance MEPS. This work summarizes the design principles, recent advances in MEPS based on SRM, and application in redox flow cells. Moreover, structure design strategies as well as in situ characterization techniques and theoretical calculations for SRM is also proposed. It is expected to promote the vigorous development of MEPS based on SRM. Finally, the challenges and perspectives of MEPS based on SRM are discussed.

Electroreductive Cross-Electrophile Coupling (eXEC) Reactions

Electrochemistry utilizes electrons as a potent, controllable, and traceless alternative to chemical oxidants or reductants, and typically offers a more sustainable option for achieving selective organic synthesis. Recently, the merger of electrochemistry with readily available electrophiles has been recognized as a viable and increasingly popular methodology for efficiently constructing challenging C-C and C-heteroatom bonds in a sustainable manner for complex organic molecules. In this mini-review, we have systematically summarized the most recent advances in electroreductive cross-electrophile coupling (eXEC) reactions during the last decade. Our focus has been on readily available electrophiles, including aryl and alkyl organic (pseudo)halides, as well as small molecules such as CO2 , SO2 , and D2 O.

Electrochemical NiH-Catalyzed C(sp3 )-C(sp3 ) Coupling of Alkyl Halides and Alkyl Alkenes

Herein, an electrochemically driven NiH-catalyzed reductive coupling of alkyl halides and alkyl alkenes for the construction of Csp3 -Csp3 bonds is firstly reported. Notably, alkyl halides serve dual function as coupling substrates and as hydrogen sources to generate NiH species under electrochemical conditions. The tunable nature of this reaction is realized by introducing an intramolecular coordinating group to the substrate, where the product can be easily adjusted to give the desired branched products. The method proceeds under mild conditions, exhibits a broad substrate scope, and affords moderate to excellent yields with over 70 examples, including late-stage modification of natural products and drug derivatives. Mechanistic insights offer evidence for an electrochemically driven coupling process. The sp3 -carbon-halogen bonds can be activated through single electron transfer (SET) by the nickel catalyst in its low valence state, generated by cathodic reduction, and the generation of NiH species from alkyl halides is pivotal to this transformation.