Dramatic Size‐dependence of Rhn+ Clusters in Reacting with Small Hydrocarbons: Rh3+ Cluster Catalysis for Dehydrogenation

Abstract We report a joint experimental and theoretical study of the gas‐phase reactions between rhodium clusters Rh n + (n=1–24) and small hydrocarbons. It is found that most Rh n + clusters react with CH 4 to form absorption products Rh n (CH 4 ) 1,2 + but Rh 3 + reacts to form carbide indicative of complete dehydrogenation; Rh 2 + reacts with CH 4 to form partial dehydrogenation products Rh 2 CH 2 + and Rh 2 C 2 H 6 + . The distinctive reactivity of Rh 3 + is also found for the reactions with C 2 H 2 , C 2 H 4 and C 2 H 6 , where the complete dehydrogenation product Rh 3 C 2 + is also formed. Analysis of reaction kinetics demonstrates that the cooperation of three Rh atoms plays a key role in the dehydrogenation reaction. Notably, Rh 3 + bears a large HOMO‐LUMO gap and reasonable stablity, and the roughly equal contribution of electrostatic and orbital interactions provide advantages to form two symmetric Rh−H−C hydrogen bridge bonds which promote the synergic cluster catalysis for hydrogen atom transfer and C−H bond dissociation. The efficient dehydrogenation mediated by an Rh 3 + cluster opens a window to design new catalysts for C−H activation.