A Hybrid Catalyst for Light-Driven Green Molecular Transformations

This Minireview is focused on the development of hybrid catalysts composed of photosensitizers and a metal complex, especially vitamin B₁₂ derivatives. The semiconductor–metal complex composites are effective photocatalysts for molecular transformations due to the synergistic effect between the two components. The design of a B₁₂ complex for the hybridization with TiO₂ was simple and straightforward—cobyrinic acid, having seven carboxylic groups derived from naturally occurring B₁₂ is stably immobilized on the TiO₂. By using the hybrid catalysts as mimics of B₁₂-dependent enzymes, light-driven reactions such as the dechlorination of organic halide pollutants, and radical-mediated isomerization proceeded catalytically. In addition to the enzyme-mimicking reactions, bioinspired reactions were also developed with the hybrid catalyst. The B₁₂–TiO₂ hybrid catalyst was used for hydrogen evolution and alkene reduction by UV light irradiation, and the cobalt–hydrogen complex (Co–H complex) was considered to be a putative intermediate of the reactions. The multidisciplinary concept for the design of a hybrid catalyst is described in this Minireview.