Immobilization of Molecular Catalysts for Enhanced Redox Catalysis

In the homogenous phase, redox catalysts are often deactivated by bimolecular reactions. For example, the charge-separated state of photoredox catalysts decayed via bimolecular back electron transfer reactions between the charge-separated molecules to decrease the lifetimes of the catalytically active species. When photoredox catalysts are immobilized on solid supports, the lifetime of the charge-separated state was remarkably elongated to enhance the photocatalytic activity. Immobilization of photoredox catalysts on electrodes is required for photocurrent generation, leading to development of solar cells. Metal-oxygen intermediates, which are active for oxidation of various substrates including water oxidation, are also deactivated via bimolecular reactions to produce inactive forms such as dinuclear metal bis-μ-oxo complexes. Immobilization of metal complex catalysts on solid supports prohibits the bimolecular deactivation, enhancing the catalytic activity and stability. This Review focuses on recent development of immobilization of both organic and inorganic molecular catalysts on various supports for enhancement of the catalytic activity, selectivity and stability in thermal and photoinduced redox reactions.