Identifying Intermediates in Electrocatalytic Water Oxidation with a Manganese Corrole Complex

Area of Science:

• Inorganic Chemistry
• Electrochemistry
• Catalysis

Background:

• Water nucleophilic attack (WNA) is a proposed mechanism for O-O bond formation in water oxidation.
• Manganese-oxo species are key intermediates in both natural and artificial water oxidation processes.

Purpose of the Study:

• To investigate the electrocatalytic water oxidation mechanism using a manganese corrole complex (1).
• To elucidate the role of water nucleophilic attack (WNA) in O-O bond formation by a manganese complex.

Main Methods:

• Electrocatalysis in propylene carbonate (PC).
• Spectroscopic identification of intermediates (UV-vis, EPR, IR).
• Isotope labeling experiments.
• Density functional theory (DFT) calculations.

Main Results:

• Oxygen evolution was observed with hydroxide and water, but at different potentials.
• A Mn(V)=O complex reacted significantly faster with hydroxide (k2 = 7.4 × 10^3 M^-1 s^-1) than water (k2 = 4.4 × 10^-3 M^-1 s^-1).
• A Mn(IV)-peroxo species, derived from water, was identified during electrolysis, supporting the WNA mechanism.

Conclusions:

• The study provides evidence for the involvement of the water nucleophilic attack (WNA) mechanism in manganese-catalyzed water oxidation.
• While direct WNA to Mn(V)=O is unlikely, WNA involving hydroxide or oxidized Mn(V)=O species are plausible pathways.
• The findings contribute to understanding O-O bond formation in artificial photosynthesis and catalysis.