Two Carbon Dioxide Molecules Consecutively Reduced by Metal-Free B₂O₂^- Anions

Compared with transition metals, nonmetallic elements have always been considered to have low reactivity toward carbon dioxide. However, in recent years, main-group compounds such as boron-based species have gradually attracted increasing attention due to their prospective applications in different kinds of reactions. Herein, we report that metal-free anions B₂O₂^- can promote two CO₂ reductions, producing the oxygen-rich product B₂O₄^-. In most of the reported CO₂ reduction reactions mediated by transition-metal-containing clusters, transition metals usually provide electrons for the activation of CO₂; one oxygen atom in CO₂ is transferred to metal atoms, and CO is released from the metal atoms. In sharp contrast, B atoms are electron donors in the current systems and the formed CO is liberated directly from the activated CO₂ unit. The synthesis of novel-metal-free gas-phase clusters and investigation of their reactivity toward carbon dioxide as well as reaction mechanisms can provide a fundamental basis in practice for the rational design of active sites on metal-free catalysts.