(PSiP)Ni-Catalyzed (E)‑Selective Semihydrogenation of Alkynes with Molecular Hydrogen

The selective semihydrogenation of alkynes to (E)-alkenes is a challenging transformation that is of significant synthetic interest. The development of direct hydrogenation catalysts for this transformation that are based on earth-abundant 3d transition metals and are tolerant of diverse functional groups is highly sought after. We report herein that the bis­(phosphino)­silyl Ni hydride complex (iPr-PSiPInd)­NiH (1) is an effective pre-catalyst for the (E)-selective semihydrogenation of a broad range of diaryl alkynes and SiMe3-protected terminal alkynes. Complex 1 exhibits this reactivity under mild conditions (1 atm H2, 25–50 °C, and 1–2.5 mol % Ni) to afford the corresponding (E)-alkenes with high selectivity. Stoichiometric experiments reveal that facile alkyne insertion and subsequent alkene isomerization lead to the observed selectivity.