Density Functional Theory Mechanistic Study of Ni-Catalyzed Reductive Alkyne–Alkyne Cyclodimerization: Oxidative Cyclization versus Outer-Sphere Proton Transfer

Density functional theory mechanistic study of the nickel-catalyzed reductive alkyne–alkyne cyclodimerization with CH₃OH/BEt₃ unveils that, after forming a nickel-alkyne π complex, the reaction prefers outer-sphere proton transfer rather than the common alkyne–alkyne oxidative cyclization. The outperformance of aminophosphine ligand (L1) is attributed to its bidentate coordination that favors the proton transfer, the labile −NH₂ and strong electron-donating −PPh₂ arms and adequate Ni–P distance that allow the hydrogen transfer of the ethyl group of MeO-BEt₃^–.