Transfer Hydrogenation in Mesoporous Palladium: Polar Hydrogen Engineering to Realize High Selectivity of Alkyne Semi‐Hydrogenation

Abstract Semi‐hydrogenation of alkynes to industrially important alkenes is earnestly desirable in the fine chemical industry but energetically unfavorable. Herein, it is reported that mesoporous palladium ( meso ‐Pd) catalyst changes the hydrogenation pathways in ethanol with ammonium borane as the hydrogen source, realizing the high catalytic selectivity of ≈99% in semi‐hydrogenation of alkynes. Mechanism studies reveal that the active polar hydrogen can be produced and reserved well in the electron‐rich mesoporous channels of meso ‐Pd catalyst, resulting in a transfer hydrogenation pathway, which selectively semi‐hydrogenates alkynes into alkenes without over‐hydrogenating alkenes into alkanes. Moreover, it is demonstrated that the polar hydrogen engineering of meso ‐Pd catalyst is highly efficient in various alkyne semi‐hydrogenation and chemoselective hydrogenation reactions. The results thus establish metal catalyst mesostructuring as an alternative route for engineering polar hydrogen in the transfer hydrogenation reactions, thus realizing the high catalytic selectivity in various selective catalysis.