Electrochemically Driven Selective Olefin Epoxidation by Cobalt-TAML Catalyst.

Area of Science:

• Green Chemistry
• Catalysis
• Electrochemistry

Background:

• Thermochemical conversion of epoxides faces challenges including harsh conditions and greenhouse gas emissions.
• Epoxides are crucial intermediates in manufacturing diverse industrial products.
• Developing sustainable alternatives for epoxide synthesis is essential.

Purpose of the Study:

• To develop an alternative, sustainable electrocatalytic method for olefin epoxidation.
• To utilize a molecular catalyst, [Co^III(TAML)]^-, for efficient and selective epoxidation.
• To investigate the reaction mechanism and identify active intermediates.

Main Methods:

• Electrocatalytic epoxidation using [Co^III(TAML)]^- catalyst.
• Utilizing water as the oxygen atom source under ambient conditions.
• Employing electrokinetic studies, operando voltammetry-electrospray ionization mass spectrometry (VESI-MS), and electron paramagnetic resonance (EPR) for mechanistic insights.

Main Results:

• The [Co^III(TAML)]^- catalyst demonstrated high selectivity (>90%) and Faradaic efficiency (>60%) for cyclohexene epoxidation.
• The catalyst exhibited a broad substrate scope for olefin epoxidation.
• A proton-coupled electron transfer process was identified as the rate-limiting step, forming reactive cobalt-oxygen species.

Conclusions:

• The [Co^III(TAML)]^- catalyst offers an efficient and sustainable alternative to traditional thermochemical epoxidation.
• This electrocatalytic approach provides a new pathway for producing valuable chemical feedstocks.
• The findings pave the way for greener chemical synthesis using electrochemical methods.