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 pi 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-.