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

Mechanism of Rhodium-Catalyzed Formyl Activation: A Computational Study

Metal-catalyzed transfer hydroformylation is an important way of cleaving C–C bonds and constructing new double bonds. The newly reported density functional theory (DFT) method, M11-L, has been used to clarify the mechanism of the rhodium-catalyzed transfer hydroformylation reported by Dong et al. DFT calculations depict a deformylation and formylation reaction pathway. The deformylation step involves an oxidative addition to the formyl C–H bond, deprotonation with a counterion, decarbonylation, and β-hydride elimination. After olefin exchange, the formylation step takes place via olefin insertion into the Rh–H bond, carbonyl insertion, and a final protonation with the conjugate acid of the counterion. Theoretical calculations indicate that the alkalinity of the counterion is important for this reaction because both deprotonation and protonation occur during the catalytic cycle. A theoretical study into the formyl acceptor shows that the driving force of the reaction is correlated with the stability of the unsaturated bond in the acceptor. Our computational results suggest that alkynes or ring-strained olefins could be used as formyl acceptors in this reaction