Catalysts for water reduction in artificial photosynthesis could be useful for the production of sustainable energy. However, the large scale of energy production requires cheap and highly scalable approaches. For the synthesis of organic chemicals, in contrast, the demands on catalysts are not as harsh. Thus, catalytic systems for water reduction, which turned out to be too expensive or unselective, could be repurposed for organic reactions.

Julio Lloret-Fillol, Institute of Chemical Research of Catalonia (ICIQ), Tarragona, and Catalan Institution for Research and Advanced Studies (ICREA), Barcelona, both Spain, and colleagues have developed a light-driven synthesis for the reduction of ketones and aldehydes that is based on a cobalt-complex water-reduction catalyst. To create the catalytic system, the team combined an aminopyridine cobalt complex that catalyzes water reduction with the copper photoredox catalyst [Cu(bathocuproine)(Xantphos)](PF₆) (bathocuproine = 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, Xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene). In addition, a combination of water and electron-donating amines such as Et₃N serves as a hydride source for the reduction reaction.

The catalytic system is able to reduce aldehydes and aromatic ketones to the respective alcohols. The Co-Cu catalyst shows highly selective activity for the reduction of organic compounds over water reduction. The method also allows the easy synthesis of deuterated alcohols by replacing regular water with D₂O.

• Dual cobalt–copper light-driven catalytic reduction of aldehydes and aromatic ketones in aqueous media,
  Arnau Call, Carla Casadevall, Ferran Acuña-Parés, Alicia Casitas, Julio Lloret-Fillol,
  Chem. Sci. 2017.
  DOI: 10.1039/c7sc01276d