The ligand effect on the selective C–H versus C–C bond activation of propane by NiBr+: a theoretical study

Abstract

Density functional theory has been employed to investigate the ligand effect in the reaction of ligated NiBr+ with propane. Both initial C–H and C–C bond activation mechanisms for losses of HBr, H2, and CH4 are analyzed in terms of the topology of the potential energy surface. Losses of HBr and H2 involve three C–H activation mechanisms, that is, α,β-H, α,γ-H, and β,α-H abstractions, where the last β,α-H abstraction is the most favorable mechanism. Loss of CH4 involves initial C–C activation, but it is prevented by the high-energy barrier. When propane reacts with the open-shell ligated NiBr+, the ligand of Br in the initial C–H activation could direct abstract a H atom from propane substrate via a four-center transition state, without forming multi-σ-type bonding of Ni+, whereas the metal center in the initial C–C activation needs to experience an unfavorable three σ-type bonding (with Br, CH3, and CH2CH3), which explains why HBr and H2 are formed in the reaction of BrNi+/C3H8 and CH4 not.