Metal atoms and clusters exhibit chemical properties that are significantly different or totally absenti nc omparison 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 providedf undamentali nsights into their intrinsic reactivity,t hus leadingt oaguidingp rinciple for the rational design of the single-atom and cluster-based catalysts. Especially,r ecent gas-phase studies have elucidated that small molecules such as O 2 ,C O 2 ,a nd CH 3 Ic an be catalytically activated by negatively-chargeda toms/clusters via donation of apartial 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 ac orrelation between their activation modes and the electronic structures might be helpful for the future development of innovative coinagem etal catalysts. Figure 1. (a) Schematic image of the electronic shell model. Magic Au clusters are shown as examples. (b) EA of Au clusters as af unction of cluster size. Downward triangles and solid lines representthe experimentalv alues and those prediction by the superatom model, respectively.Reprinted from Ref. [14] with permission for (b).