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 Rh_nC_xH_yI_z⁺ species (x = 1–4, y = 1–12, and z = 1–5) pertaining to H₂, 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.