Iridium-Catalyzed Selective Hydrogenation of α,β-Unsaturated Aldehydes to Allylic Alcohols

Ir-BiphPAP catalysts, featuring biphenyl-derived pyridine-aminophosphine ligands, are reported for the selective hydrogenation of α,β-unsaturated aldehydes. These Ir-PNN catalysts enable the highly active and selective hydrogenation of the C═O bond of α,β-unsaturated aldehydes to afford allylic alcohols. In particular, catalyst <b>1b</b>, incorporating 5,5'-di-<i>tert</i>-butyl groups on the biphenyl ring of the ligand, effectively converts a variety of α,β-unsaturated aldehydes into allylic alcohols with high yields and excellent selectivity, and the turnover number is as high as 78,000.