Two Carbon Dioxide Molecules Consecutively Reduced by Metal-Free B 2 O 2 - 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 B 2 O 2 - can promote two CO 2 reductions, producing the oxygen-rich product B 2 O 4 - . In most of the reported CO 2 reduction reactions mediated by transition-metal-containing clusters, transition metals usually provide electrons for the activation of CO 2 ; one oxygen atom in CO 2 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 CO 2 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.