Search

A density functional theory method was employed to investigate the mechanism of C-O bond activation of butanoic acid substrates bearing the 8-aminoquinoline (AQ) group catalyzed by Pd(OAc)2. The whole reaction consists of five fundamental steps: the chelation of substrate A1, the C-H activation step, the C-N coupling step, the protodepalladation step, and the release of the final product. The calculated results indicated that the protodepalladation step is the rate-determining step with a free energy barrier of 24.3 kcal/mol. This theoretical study pointed out that the energy barriers of C-H activation in the presence and absence of AQ are 11.3 and 26.6 kcal/mol, respectively. This is to say that the installation of the AQ directing group is critical to the regioselectivity of C-H activation and the β-O elimination steps, and this reason enables selective activation of the γ C-O bond. Furthermore, this chelating functionality facilitated the protodepalladation step because the energy barrier of the protodepalladation step was decreased with the coordination of the AQ directing group with a Pd center, and that was 39.3 kcal/mol in the absence of AQ. This also explains why no product formation was observed in the experiment upon changing the directing AQ group to a phenylamino group. Finally, other substrates bearing the phenol leaving group at the β- and δ-positions of carbonyl were investigated in order to expand the applicability of the AQ directing strategy. This work could provide new theoretical insights into the activation of strong alkyl C(sp3) covalent bonds via the AQ directing strategy.

A density functional theory (DFT) study has been performed to investigate the mechanism of ruthenium-catalyzed deoxygenative hydroboration of carboxylic acid. The reduction of the carbonyl motif is suggested to proceed via an intramolecular 1,3-hydride shift mechanism. The second HBpin coordination intermediate with the Ru center could facilitate the pinBOBpin reductive elimination and the PhCH2OBpin reductive elimination step. The energy span for the reaction is 25.2 kcal mol−1.

The reaction mechanisms of the hydrogenation of [(η5-C5H2-1,2,4-Me3)2Hf]2(NCO) (μ2-N) (1) were studied using density functional theory (DFT) method. The calculated results indicate that the first step is the addition of H2 to the Hf N double bond, the second step is the insertion of isocyanate into the bridging metal hydride. The metal centers with a low electronegativity benefits the hydrogenation of 1. Then the reaction mechanisms of allenes with 1 were also investigated. The calculated results imply that the allenes with larger hindrance tend to undergo 1,2 addition with 1, the allenes with smaller hindrance tend to undergo 2+2 cycloaddition with 1, which is in good agreement with experimental results.