Reductive Activation of Small Molecules by Anionic Coinage Metal Atoms and Clusters in the Gas Phase.

Metal atoms and clusters exhibit chemical properties that are significantly different or totally absent in comparison to their bulk counterparts. Such peculiarity makes them potential building units for the generation of novel catalysts. Investigations of the gas-phase reactions between size- and charge-selected atoms/clusters and small molecules have provided fundamental insights into their intrinsic reactivity, thus leading to a guiding principle for the rational design of the single-atom and cluster-based catalysts. Especially, recent gas-phase studies have elucidated that small molecules such as O2 , CO2 , and CH3 I can be catalytically activated by negatively-charged atoms/clusters via donation of a partial electronic charge. This Minireview showcases typical examples of such "reductive activation" processes promoted by anions of metal atoms and clusters. Here, we focus on anionic atoms/clusters of coinage metals (Cu, Ag, and Au) owing to the simplicity of their electronic structures. The determination of a correlation between their activation modes and the electronic structures might be helpful for the future development of innovative coinage metal catalysts.