Mechanism of Ruthenium-Catalyzed Direct Arylation of C–H Bonds in Aromatic Amides: A Computational Study

Ruthenium-catalyzed arylation of
ortho C–H bonds directed by a bidentate 8-aminoquinoline moiety
not only is important to construct new biaryl derivates but also merges
important research areas. In this study, the density functional theory
(DFT) method M11-L was employed to predict the mechanism of this C–H
bond arylation reaction. The computational results indicate that the
initial step for this reaction is catalyst loading by electrophilic
deprotonation to generate a substrate-coordinated Ru­(II) intermediate,
which is the key compound in the complete catalytic cycle. The catalytic
cycle includes electrophilic deprotonation by carbonate, oxidative
addition of bromobenzene, reductive elimination to form a new aryl–aryl
bond, proton transfer to release the product, and ligand exchange
to regenerate the initial Ru­(II) intermediate. Theoretical calculations
suggest that the oxidative addition of bromobenzene is the rate-determining
step of the whole catalytic cycle, and the apparent activation free
energy is 32.7 kcal/mol. The ligand effect was considered in DFT calculations,
and the calculated results agree well with experimental observations.