Polystyrene-Cross-Linking Triphenylphosphine on a Porous Monolith: Enhanced Catalytic Activity for Aryl Chloride Cross-Coupling in Biphasic Flow

Immobilized transition metals for continuous-flow catalyses are greatly in demand to achieve automation, scale-up, facile separation, regeneration, and energy-saving production with high level of sustainability and efficiency. Here, we report a tertiary phosphine immobilized on a macroporous monolith (M-PS-TPP) for the challenging Pd-catalyzed cross-coupling reaction of aryl chloride in a continuous-flow system. The monolithic and macroporous structure of M-PS-TPP was fabricated by bulk polymerization in the presence of a high internal phase emulsion (HIPE) template. Owing to the large pore size and high porosity, the M-PS-TPP showed high permeability against continuous flow of the mobile phase. The continuous-flow Suzuki-Miyaura cross-coupling reaction was realized by permeation of organic/aqueous media containing inorganic salt through a Pd-loaded monolith (M-PS-TPP-Pd) column without serious clogging. Controlling coordination chemistry and hydrodynamics of M-PS-TPP-Pd boosted highly active phosphine-metal complex formation and fast mass transfer of reactants. Indeed, the M-PS-TPP-Pd column showed surprisingly higher yields (∼93%) and turnover numbers (2704) under continuous-flow conditions than that under batch conditions (∼6%).