Scheme 3 The proposed catalytic cycle proposed by Duan group10.
As the examples of the synthesis of alkenyl chlorides developed from a
ligand-promoted palladium-catalyzed C-H activation of internal alkynes
with simple arenes without directing groups, the reactions reported by
Duan’s group deserve further study to clarify the detailed mechanism,
e.g., the rate-determining and selectivity-determining step(s). In this
work, several key issues related to the reaction were solved using
density functional theory calculations. (1) what is the origin of
chemoselectivity of a 82: 9 ratio forPR11/PR12 when the alkyne is2a1 with L1 as the ligand ? (2) When ligandL1 is replaced with L2 , why no product ? (3) The
substituent effects on chemoselectivity should be rationalized. (4) As
previously reported, the bidentate ligand (L2 ) coordinates with
palladium acetate to form a square-planar species19.
Because the bidentate ligand L1 (2-OH-1,10-phenanthroline)
differs from L2 only by one OH group, whether the most stable
compound formed by the reaction of L1 with palladium acetate is
the same to the one formed by the coordination of ligandL2 (1,10-phenanthroline) with palladium acetate or not? This
work presents a further understanding of palladium-catalyzed C-H
arylation of alkynes with arenes and provides helpful informatiom for an
efficient design of new related reactions.