Metal-free reduction of CO to formate using a photochemical organohydride-catalyst recycling strategy.

Increasing levels of CO in the atmosphere is a problem that must be urgently resolved if the rise in current global temperatures is to be slowed. Chemically reducing CO into compounds that are useful as energy sources and carbon-based materials could be helpful in this regard. However, for the CO reduction reaction (CORR) to be operational on a global scale, the catalyst system must: use only renewable energy, be built from abundantly available elements and not require high-energy reactants. Although light is an attractive renewable energy source, most existing CORR methods use electricity and many of the catalysts used are based on rare heavy metals. Here we present a transition-metal-free catalyst system that uses an organohydride catalyst based on benzimidazoline for the CORR that can be regenerated using a carbazole photosensitizer and visible light. The system is capable of producing formate with a turnover number exceeding 8,000 and generates no other reduced products (such as H and CO).