To What Extent Do Iodomethane and Bromomethane Undergo Analogous Reactions?

Iodomethane and bromomethane (CH3I/CH3Br) are common chemicals, but their chemistry on nanometals is not fully understood. Here, we analyze the reactivity of Rh-n(+) (n = 3-30) clusters with halomethanes and unveil the spin effect and concentration dependence in the C-H and C-X bond activation. It is found that the reactions under halomethane-rich conditions differ from those under metal-rich conditions. Both CH3I and CH3Br undergo similar dehydrogenation on the Rh-n(+) clusters in the presence of small quantity reactants; however, different reactions are observed in the presence of sufficient CH3I/CH3Br, showing dominant Rh(CH3Br)(x)(+) (x = 1-4) products but a series of RhnCxHyIz+ species (x = 1-4, y = 1-12, and z = 1-5) pertaining to H-2, HI, or CH4 removal. Density functional theory calculations reveal that the dehydrogenation and demethanation of CH3Br are relatively less exothermic and will be deactivated by sufficient gas collisions if helium cooling takes away energy immediately; instead, the successive adsorption of CH3Br gives rise to a series of Rh(CH3Br)(x)(+) species with accidental C-Br bond dissociation.