Unlocking the Continuous Flow Asymmetric Hydrogenation of Olefins Through the Development of a Non-Deactivating Immobilized Iridium Catalyst

Abstract

Asymmetric hydrogenation (AH) is a leading method for producing enantiopure compounds and several industrial processes rely on its chemical efficiency. However, these processes involve noble metals and even sophisticated ligands that are costlier than the metal itself. The recovery of these expensive catalysts remains an unsolved issue. Despite efforts to develop supported catalysts for continuous-flow AH, none have been used industrially, as most suffer depletion of selectivity and/or activity (from catalyst deactivation or metal leaching), and its heterogenization often lengthens the catalyst's synthetic route. Here, we report a simple synthetic approach to air stable, Ir-P,S catalysts covalently immobilized onto polystyrene resins, without increasing the number of synthetic steps. The Ir-loaded functional resin fully retains the catalytic performance of the homogeneous Ir-complex. Remarkably, they were successfully applied to the continuous-flow AH of olefins, far beyond the typical benchmark substrates. The products are continuously produced over long periods of time with high yields and selectivities, with low residence time, even at pressures far below to the corresponding batch reaction. No deactivation or leaching of Ir is observed, and a practical simple procedure for storage and reuse of the immobilized catalysts after flow hydrogenation secures their immediate availability for extended periods of time.