Electrochemical Oxidative Cross-Coupling with Hydrogen Evolution Reactions

Abstract

CONSPECTUS:Oxidative cross-coupling has proved to be one of the most straightforward strategies for forming carbon−carbon and carbon−heteroatom bonds from easily available precursors. Over the past two decades, tremendous efforts have been devoted in this field and significant advances have been achieved. However, in order to remove the surplus electrons from substrates for chemical bonds formation, stoichiometric oxidants are usually needed. Along with the development of modern sustainable chemistry, considerable efforts have been devoted to perform the oxidative cross-coupling reactions under external-oxidant-free conditions. Electrochemical synthesis is a powerful and environmentally benign approach, which can not only achieve the oxidative cross-couplings under external-oxidant-free conditions, but also release valuable hydrogen gas during the chemical bond formation. Recently, the electrochemical oxidative cross-coupling with hydrogen evolution reactions has been significantly explored. This Account presents our recent efforts toward the development of electrochemical oxidative cross-coupling with hydrogen evolution reactions. (1) We explored the oxidative cross-coupling of thiols/thiophenols with arenes, heteroarenes, and alkenes for C−S bond formation. (2) Using the strategy of electrochemical oxidative C−H/N−H cross-coupling with hydrogen evolution, we successfully realized the C−H amination of phenols, anilines, imidazopyridines, and even ethers. (3) Employing halide salts as the green halogenating reagents, we developed a clean C−H halogenation protocol under electrochemical oxidation conditions. To address the limitation that this reaction had to carry out in aqueous solvent, we also developed an alternative method that uses CBr 4 , CHBr 3 , CH 2 Br 2 , CCl 3 Br, and CCl 4 as halogenating reagents and the mixture of acetonitrile and methanol as cosolvent. (4) We also developed an approach for constructing C−O bonds in a well-developed electrochemical oxidative cross-coupling with hydrogen evolution manner. (5) Under mild external-oxidant-free electrochemical conditions, we realized the C(sp 2 )−H and C(sp 3 )−H phosphonylation with modest to high yields. (6) We successfully achieved the S−H/S−H cross-coupling with hydrogen evolution under electrochemical oxidation conditions. By anodic oxidation instead of chemical oxidants, the overoxidation of thiols and thiophenols was well avoided. (7) The methods for constructing structurally diverse heterocyclic compounds were also developed via the electrochemical oxidative annulations. (8) We have also applied the electrochemical oxidative cross-coupling with hydrogen evolution strategy to the alkenes difunctionalization for constructing multiple bonds in one step, such as

Site-selective electrooxidation of methylarenes to aromatic acetals

“…With the optimized reaction conditions defined, we set out to explore the scope of the electrooxidation of methylarenes. Notably, the site-selectivity was not significantly affected by introducing a phenyl (3), bromo (4), or cyano group (5) at C5, or by varying the substituent on N1 (6-9) or C2 (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29) of the C4,C6-dimethylated benzimidazole substrate (Fig. 2).…”

“…However, the installation of a carbamoyl group on N1 resulted in a slight decrease of regioselectivity (10). The method showed broad compatibility with common functional groups or moieties such as alkyl bromide (7), alkyne (8), alkene (9), ester (15,16), alcohol (17,18), ketone (19), aldehyde (20), Bocprotected amine (21)(22)(23), ketal (24), azido (25), and aromatic heterocycles (12, 13, 26, and 27). Molecular fragments derived from natural products dehydroabietic acid (28) and lithocholic acid (29) were equally well tolerated.…”

“…1a). As an alternative to chemical oxidation, electrooxidation eliminates the use of stoichiometric chemical oxidants and is attracting increasing interests [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] . Notably, electrooxidation of electron-rich toluene derivatives to substituted benzaldehydes has been applied in the industrial production of panisaldehyde and 3,4,5-trimethoxybenzaldehyde [27][28][29] .…”

Prospects of Value‐Added Chemicals and Hydrogen via Electrolysis

“…A concept taking all this into consideration will combine both, electrosynthesis of high‐value chemicals in one half cell with the hydrogen evolution as the counter reaction . This in turn can be considered from two perspectives, either by integrating cathodic hydrogen production as a side reaction into oxidative electrosynthesis systems or/and by incorporating oxidative synthesis of certain chemicals instead of oxygen into water electrolysis system.…”

Constructing a Rod‐like CoFeP@Ru Heterostructure with Additive Active Sites for Water Splitting

“…Electrocatalytic water splitting into hydrogen and oxygen is one of the efficient ways to produce hydrogen as environmentallyfriendly energy. [1] Currently, the highest activity catalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is platinum (Pt) and iridium (Ir)/ruthenium (Ru) oxides, respectively, but the high price and scarcity greatly hinder their widespread adoption of industrial applications. [2,3] More importantly, the incompatibility and the sluggish kinetics for HER and OER can lead to inferior efficiency in a single watersplitting device.…”