Unlocking Interfacial Catalytic Halogen Atom Transfer at Ag Electrodes with Brønsted Acids

Area of Science:

• Organic Chemistry
• Electrochemistry
• Catalysis

Background:

• Halogen atom transfer is crucial for generating carbon-centered radicals from organic halides.
• Developing reusable heterogeneous electrocatalysts for this process requires understanding interfacial reactions.
• Activating unactivated alkyl bromides electrochemically often demands harsh conditions, limiting functional group tolerance.

Purpose of the Study:

• To investigate the role of Brønsted acids in facilitating interfacial halogen atom transfer at catalytic silver electrodes.
• To identify strategies for mild and programmable access to carbon-centered radicals using electrocatalysis.
• To demonstrate the utility of this approach in electroorganic synthesis.

Main Methods:

• Electrochemical studies and in situ spectroscopy were used to analyze reactions at the silver electrode interface.
• The effect of Brønsted acids with varying pKa values on halogen atom transfer was systematically investigated.
• Carbon-carbon bond formation reactions were performed to showcase the synthetic applicability.

Main Results:

• Brønsted acids significantly lower the overpotential required for halogen atom transfer from unactivated alkyl bromides at silver electrodes.
• In the presence of acids, halogen atom transfer occurs near the thermodynamic potential, enabling mild reaction conditions.
• Acid promotion is unique to catalytic silver surfaces and depends on the acid's pKa, with a specific threshold observed.
• Electrode passivation by halogen species is overcome by acid addition, allowing for multiple turnovers.

Conclusions:

• Brønsted acids are effective promoters of interfacial halogen atom transfer at catalytic silver electrodes.
• This acid-mediated process provides a mild and programmable route to carbon-centered radicals for electroorganic synthesis.
• The use of reusable catalytic electrodes with Brønsted acids opens new avenues for sustainable synthetic chemistry.