Transition Metal-Catalyzed Organic Reactions under Visible Light: Recent Developments and Future Perspectives

The development of transition metal (TM) catalysis for organic synthesis under visible light without recourse to typical photoredox catalysts has become a rapidly growing area of research and has been actively explored in the past several years. Distinct from the extensively developed photoredox catalysis, in which the photocatalyst generally does not directly participate in a bond-forming process, and photocatalyst/TM synergistic catalysis, in which the photocatalyst absorbs photon energy and transfers energy to the TM catalyst through a redox or energy transfer process, this Review focuses on summarizing the recent developments of photocatalytic reactions that use TM complexes to both absorb visible light and participate in catalytic bond formation involving a catalyst covalently bonded intermediate. The contents of this Review are categorized by the transition metal used (Pd, Cu, Co, Ni, Mn, Au, Rh, Fe, Ru), with a descending sequence according to the number of examples reported of each metal, and provide an overview of TM catalysis under visible light reported to April 2020. Future perspectives and personal opinions regarding this actively expanding research field are also discussed.