Stable and Versatile Pd Precursors for the Preparation of Robust Pd Catalysts Under Continuous‐Flow

Abstract

The chemical and engineering communities require the development of versatile precursors that can be used to synthesize robust catalysts to achieve global sustainability. To meet this demand, we developed a new Pd precursor for incorporating fine Pd metal into supports in a highly efficient manner. An atmospherically stable Pd precursor (Pd‐80) was prepared by the thermally promoted aerobic oxidation of tetrakis(triphenylphosphine)palladium. The physical properties of Pd‐80 were investigated using NMR spectroscopy, SEM, XPS, solvent‐relaxation NMR spectroscopy, and dynamic light scattering (DLS) experiments. We also prepared a cordierite‐supported Pd catalyst (Pd/cordierite) by stirring Pd‐80 and cordierite powder in chloroform at room temperature. Pd/cordierite selectively catalyzes the hydrogenation of various reducible functional groups, including alkynes, azides, nitro groups, olefins, CO2Bn, N‐Cbz, O‐Bn, aromatic ketones, and styrene oxide, in continuous‐flow hydrogenation reactions. The Pd/cordierite‐catalyzed continuous‐flow hydrogenation of nitrobenzene derivatives afforded the corresponding anilines, with catalyst activity maintained for over 250 h of continuous operation and a turnover number (TON) of 61,090 recorded.