To What Extent Do Iodomethane and Bromomethane Undergo Analogous Reactions?

Iodomethane and bromomethane (CHI/CHBr) are common chemicals, but their chemistry on nanometals is not fully understood. Here, we analyze the reactivity of Rh ( = 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 CHI and CHBr undergo similar dehydrogenation on the Rh clusters in the presence of small quantity reactants; however, different reactions are observed in the presence of sufficient CHI/CHBr, showing dominant Rh(CHBr) ( = 1-4) products but a series of RhCHI species ( = 1-4, = 1-12, and = 1-5) pertaining to H, HI, or CH removal. Density functional theory calculations reveal that the dehydrogenation and demethanation of CHBr are relatively less exothermic and will be deactivated by sufficient gas collisions if helium cooling takes away energy immediately; instead, the successive adsorption of CHBr gives rise to a series of Rh(CHBr) species with accidental C-Br bond dissociation.