Mechanistic insight into ligand-promoted C-H alkenylation of arenes with alkynes: A computational study

摘要

The ligand-promoted palladium-catalyzed arylation of alkynes with arenes without directing group is able to furnish alkenyl chlorides via a 1,4-chlorine migration or trisubstituted alkenes. This reaction is challenging due to bidentate N, N ligand and electron-neutral arenes have rarely been reported to afford good yields. Intrigued by the novel strategy, we carried out density functional theory calculations to unravel the ligand effects and origins of substituent-controlled chemoselectivity of the C-H functionalization reactions. For the n-propyl-substituted alkyne system, CMD process is identified as the rate-determining step. And the chemoselectivity is controlled by oxidative addition with the C-Cl bond cleavage and protonation process. While for 3,5-dimethylphenyl-substituented alkyne system, the dominant pathway turns to the protonation process. The electrostatic attractions, repulsive force and aryl substituent effects jointly result in reverse chemoselectivity. Compared with the L2 ligand, the bidentate ligand L1 reacts with palladium acetate to form a different stable square-planer species. The steric repulsion are found to be mainly responsible for the absence of products using the L2 ligand, which is different from previous reports.