Catalytic water splitting with an iridium carbene complex: a theoretical study

Area of Science:

• Inorganic Chemistry
• Catalysis
• Computational Chemistry

Background:

• Water oxidation is crucial for artificial photosynthesis and energy conversion.
• Iridium complexes are promising catalysts for water oxidation, but their reaction mechanisms are complex.
• Understanding competing reaction pathways is key to designing efficient catalysts.

Purpose of the Study:

• To elucidate the detailed catalytic mechanism of water oxidation by an iridium complex, Ir(OH)(+).
• To investigate the influence of oxidant potential on competing reaction pathways.
• To correlate computational findings with experimental observations.

Main Methods:

• Computational investigation using potential-energy surface calculations.
• Analysis of sequential oxidation steps and O-O bond formation pathways.
• Comparison of calculated reaction barriers and rates with experimental data.

Main Results:

• A multichannel reaction pathway was identified, influenced by oxidant potential.
• The most favorable mechanism involves four sequential oxidation steps prior to O-O bond formation.
• The Ir(V)(=O)(O(·))(+) species is the most stable intermediate under cerium ammonium nitrate treatment.
• O-O bond formation via coupling of oxo ligands is the rate-limiting step.
• Calculated effective barrier and turnover frequency align with experimental results.

Conclusions:

• The proposed catalytic mechanism accurately reflects experimental observations and rate laws.
• Oxidant strength dictates the preferred water oxidation pathway.
• This work provides fundamental insights into iridium-catalyzed water oxidation, aiding catalyst design.