A Heterogeneous Metal–LigandBifunctional Catalystfor Chemoselective Hydrogenation of α,β-Unsaturated Aldehydes

Abstract

Abstract The concept of metal–ligand bifunctional catalysts has been extensively explored in homogeneous catalysis, yet it has not been reported in conventional heterogeneous catalysis. Inspired by the outer-sphere hydrogenation mechanism in homogeneous metal–ligand bifunctional catalysts, we here find that an Ir single-atom catalyst with a predominantly Ir1–P4 coordination structure behaves as a heterogeneous metal–ligand bifunctional catalyst exclusively favoring the hydrogenation of the C═O bond over the C═C bond in α,β-unsaturated aldehydes─an industrially important but highly challenging transformation. The hydrogenation process is revealed to proceed through a Noyori-type transition state during the 1,2-addition pathway at the Ir–P bifunctional sites, as evidenced by combining the in situ two-dimensional 1H–1H spin diffusion and 1H–31P heteronuclear correlation nuclear magnetic resonance spectroscopy, apparent reaction order test, kinetic isotope effect analysis, and density functional theory calculations. This work demonstrates a new type of heterogeneous metal–ligand bifunctional catalyst for the chemoselective hydrogenation of α,β-unsaturated aldehydes to unsaturated alcohols and sheds light on the hydrogenation mechanism.