NiII-Catalyzed Enantioselective Anti-Markovnikov Hydrophosphination of Unactivated Alkynes

Abstract

A mechanism-inspired, reaction mode-controlled enantio- and regioselective anti-Markovnikov hydrophosphination of unactivated alkynes was accomplished by NiII catalysis. Alkenyl phosphine products could be obtained with high regio- and enantioselectivity and easily derivatized to structurally diverse chiral phosphine compounds. Mechanistic studies on both Ni0-catalyzed Markovnikov addition and NiII-catalyzed anti-Markovnikov addition have been carried out by combining experimental and computational methods. In the Ni0 system, an allyl nickel complex was obtained as the catalyst resting state whose structure was unambiguously determined by single-crystal XRD analysis. A sequential hydrometallation, ligand exchange, and reductive elimination mechanism was elucidated corroboratively by DFT calculations. In the NiII system, the cationic secondary phosphine nickel complex serves as the active catalyst. A migratory insertion and protonation sequence was operative to accomplish anti-Markovnikov hydrophosphination.