Mechanistic insights into the α-branched amine formation with pivalic acid assisted C–H bond activation catalysed by Cp*Rh complexes

Abstract

Density functional theory computations revealed a pivalic acid assisted C–H bond activation mechanism for rhodium catalyzed formation of α-branched amines with C–C and C–N bond couplings. The reaction energies of the [Cp*RhCl₂]₂ dimer and silver cations indicate that the Cp*RhCl⁺ cation is the active catalyst. The essential role of pivalic acid is a co-catalyst for the activation of the ortho-C(sp²)–H bond in phenyl(pyrrolidin-1-yl)methanone, while the reaction of NaHCO₃ and HCl reduces the overall barrier of the catalytic cycle. In the presence of both pivalic acid and NaHCO₃ in the reaction, the C(sp²)–H bond is activated through a concerted metallation deprotonation process, and the C–C bond coupling is the rate-determining step with a total free energy barrier of 23.9 kcal mol⁻¹. Without pivalic acid and NaHCO₃, the C(sp²)–H bond can only be activated through a σ-bond metathesis process and the free energy barrier increases to 32.2 kcal mol⁻¹. We also investigated the mechanisms of a side reaction for β-branched amine formation and the reaction without styrene and found that their free energy barriers are 33.4 and 30.5 kcal mol⁻¹, respectively.