Li R, Yang X. Mechanistic insights into the α-branched amine formation with pivalic acid assisted C-H bond activation catalysed by Cp*Rh complexes.
Dalton Trans 2021;
50:12888-12895. [PMID:
34581328 DOI:
10.1039/d1dt01890f]
[Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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.
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