Photosynthesis is a biochemical reaction that converts carbon dioxide and water into carbohydrates and concomitantly stores the energy of sunlight into the products (carbohydrates) as chemical energy. In photosynthetic reactions, solar energy is converted to electrochemical energy via charge separation, and the resulting electrochemical potentials triggers multi-electron redox reactions of small molecules. To artificially reproduce the photosynthetic reactions, our group has investigated the development of molecular catalysts for electro- or photochemical small-molecule conversions involving multi-electron transfer. These studies can be an important science and technology that contributes to solving energy and resource problems. In this talk, recent achievements in our group regarding the development of pentanuclear complexes as active centers for electro- or photoochemical small-molecule conversions will be presented.1-3