Photoredox Catalysis Using Heterogenized Iridium Complexes*.

Area of Science:

• Sustainable chemistry
• Materials science
• Catalysis

Background:

• Heterogenized photoredox catalysts offer tunable and reusable options for sustainable chemical synthesis.
• Iridium complexes are effective photoredox catalysts, but their heterogenization is key for practical applications.

Purpose of the Study:

• To assemble and evaluate heterogenized iridium complexes on various metal oxide surfaces (ITO, ZrO2, Al2O3) as photoredox catalysts.
• To identify optimal support materials and construct types (thin film vs. nanopowder) for efficient and sustainable catalysis.
• To assess catalyst reusability and performance in a model reductive dehalogenation reaction.

Main Methods:

• Covalent attachment of iridium complexes to metal oxide surfaces (ITO, ZrO2, Al2O3) to create heterogenized catalysts.
• Fabrication of catalysts in thin film and nanopowder formats.
• Testing catalyst performance using the reductive dehalogenation of bromoacetophenone to acetophenone as a model reaction.
• Evaluating reaction kinetics, conversion, yield, and catalyst reusability.

Main Results:

• All heterogenized iridium catalyst constructs achieved high conversions and yields of acetophenone.
• Catalysts supported on aluminum oxide (Al2O3) exhibited the fastest reaction rates, completing the test reaction in as little as fifteen minutes.
• Nanopowder catalysts generally showed faster and more efficient catalysis compared to thin film catalysts.
• Thin film catalysts demonstrated superior robustness and ease of reuse, with potential for photoelectrochemical applications.
• All catalysts were reusable 2-3 times, with Al2O3-supported catalysts achieving over 1000 turnovers, confirming their sustainability.

Conclusions:

• Heterogenized iridium catalysts on metal oxide supports are a viable and sustainable alternative for chemical synthesis.
• Aluminum oxide supports, particularly in nanopowder form, offer highly efficient catalytic systems.
• Thin film heterogenized catalysts present promising avenues for integrated photoelectrochemical and electrochemical photoredox systems.
• The reusability and high turnover numbers underscore the environmental and economic benefits of these catalytic constructs.