Ligand-Controlled Regiodivergent Palladium-Catalyzed Hydrogermylation of Ynamides

Ynamides
are fascinating small molecules with complementary reactivities
under radical, ionic, and metal-catalyzed conditions. We report herein
synthetic and DFT investigations of palladium-catalyzed ligand-controlled
regio­divergent hydrometalation reactions of ynamides. Germylated
and stannylated enamides are obtained with excellent α,E- or β,E-selectivities and a broad
functional group tolerance. Such a regio­divergent palladium-catalyzed
process is unique in ynamide chemistry and allows for the elaboration
of metalated enamides that are useful building blocks for cross-coupling
reactions or heterocyclic chemistry. DFT calculations fully support
the experimental data and demonstrate the crucial roles of the trans-geometry of the [H-Pd­(L)-Ge] complex, as well as of
the steric requirements of the phosphine ligand. In addition, these
calculations support the prevalence of a hydro-palladation pathway
over a metal palladation of the π system of the ynamide.