Isolation of a Ru(IV) side-on peroxo intermediate in the water oxidation reaction

The electrons that nature uses to reduce CO2 during photosynthesis come from water oxidation at the oxygen-evolving complex of photosystem II. Molecular catalysts have served as models to understand its mechanism, in particular the O-O bond-forming reaction, which is still not fully understood. Here we report a Ru(IV) side-on peroxo complex that serves as a 'missing link' for the species that form after the rate-determining O-O bond-forming step. The Ru(IV) side-on peroxo complex (eta(2)-1(IV)-OO) is generated from the isolated Ru(IV) oxo complex (1(IV)=O) in the presence of an excess of oxidant. The oxidation (IV) and spin state (singlet) of eta(2)-1(IV)-OO were determined by a combination of experimental and theoretical studies. O-18- and H-2-labelling studies evidence the direct evolution of O-2 through the nucleophilic attack of a H2O molecule on the highly electrophilic metal-oxo species via the formation of eta(2)-1(IV)-OO. These studies demonstrate water nucleophilic attack as a viable mechanism for O-O bond formation, as previously proposed based on indirect evidence

Artificial Photosynthesis: An Approach for a Sustainable Future

International audienceThe energy needs of humankind has experimented a sharp increase since the beginning of the Anthropocene due to a large increase in population and the evolution of our society’s lifestyle. Recent projections suggest that it will likely lead to a major crisis due to environmental issues associated with the increasing use of fossil fuel as major energy source, as well as due to a rapid dwindling of the classical and easily accessible fossil-fuels stocks. These issues require a quick response if the lifestyle adopted by our societies shall be sustained. Several solutions have been envisioned to tackle these problems, of which, the development of Artificial Photosynthetic systems is one of the most appealing. The field of artificial photosynthesis takes Nature itself as a source of inspiration, to propose alternative energy harvesting and storage strategies. This field of research not only aims at mimicking the main processes that permitted photosynthetic organisms to thrive and become the most successful autotrophs on earth, but as well at improving and optimizing these processes using synthetic materials. In this chapter, the underlying mechanisms that enable photosynthetic organisms to convert (and store) solar energy into a directly usable chemical energy will be discussed. Then it will be explained how these concepts can be extended to artificial systems and ultimately used to our own benefit