4 Conclusion
We investigated the detailed mechanism and chemoselectivity in the ligand-promoted PdII-catalyzed C–H alkeylation of internal alkynes with simple arenes without directing group using DFT calculation. The calculated results revealed that the substituents (R) in alkyne 2a effect on the mechanism and the chemoselectivity: when R is n-propyl (alkyl) group, the major product is alkenyl chloride and the rate-determining step of the catalytic reaction is the concerted metalation-deprotonation (CMD) process. The origins of chemoselectivity are related to oxidative addition with the C-Cl bond cleavage and protonation process. While R is 3,5-dimethylphenyl (aryl) group, the reaction almost exclusively afford the corresponding trisubstituted olefins and the key step of the reaction is protonation process. Reductive elimination relative to protonation process is responsible for the large barrier difference. The electrostatic attractions between Pd &C3 and Pd &Cl, repulsive force between C2 and Cl atom and a electron density decrease of alkynyl carbon caused by the aryl substituent result in reverse chemoselectivity. Bidentate ligand L1(2-OH-1,10-phenanthroline) reacts with Pd(OAc)2 to form a most stable square-planer species bearing only one bidentate acetate anion on the palladium atom, which is different from the structure formed by the coordiantion of ligand L2 (1,10-phenanthroline) with palladium acetate. The OH group of ligand is crucial to the C(sp2)-H bond cleavage of aromatic ring through CMD process. Theoretical results provide valuable information for a better understanding of the ligand effects and substituent-controlled chemoselectivity in Pd-catalyzed C-H arylation of alkynes with simple arenes to furnish trisubstituted alkenes or vinyl chlorides through a 1,4-chlorine migration.