A Mild and Efficient Iridium‐Catalyzed Method for Aldimine Hydrogenation

A mild and applicable protocol for aldimine hydrogenation has been developed using a bidentate iridium‐ N ‐hetrocyclic carbene‐phosphine catalyst. Through a series of optimization studies, twenty‐nine aldimine substrates have been successfully reduced to their corresponding amines in high isolated yields up to 99%. The developed methodology employs a low catalyst loading of just 1 mol% and proceeds under mild conditions, including under an atmospheric pressure of hydrogen gas. The process benefits from a broad solvent applicability, including notable green solvents, and tolerates aldimine substrates of varying solubility. Alongside, N ‐aryl‐based aldimine substrates, the general protocol also accomodates more challenging N ‐alkyl species without the requirement of any further additive. From a mechanistic perspective, density functional theory calculations have been utilized to examine the formation, and subsequent reaction, of a crucial iridacycle intermediate, while also revealing that the CH activation step is key for successful imine reduction. This mechanistic insight is then used to significantly elevate the performance of two poorer performing substrates.