Organometal-bridged PMOs as efficiency and reusable bifunctional catalysts in one-pot cascade reactions

Two bifunctional catalysts with two kinds of organometals incorporated into the periodic mesoporous organosilica (PMO) supports, denoted as Rh/Pd@PMO(Ph) catalyst and Fe/Cp*Rh@PMO(Et) chiral catalyst, were synthesized by surfactant directed co-condensation between phenyl (Ph)- or ethyl (Et)-bridged and organometal-bridged silanes. Two bifunctional catalysts exhibited high activities and selectivities and even high ee values in one-pot two-step cascade reactions comprised Rh(I)-catalyzed methylenation and Pd(II)-catalyzed Heck reaction, or Fe(III)-catalyzed hydrolysis and Cp*Rh-catalyzed asymmetric hydrogenation. The promoting effects from the ordered mesoporous structure, the coordination model, and the synergic effect between two kinds of active sites were discussed based on the detailed characterizations. Their catalytic efficiencies were comparable with the corresponding homogeneous catalysts and could be easily recycled and used repetitively, which could greatly reduce the cost and diminish the environmental pollutions from heavy metal ions.

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► Bifunctional catalysts were prepared by surfactant-directed co-condensation.
► Organometal incorporated into silica walls of periodic mesoporous organosilica.
► Synergic effect between two kinds of active sites.
► High catalytic efficiency and strong durability in one-pot cascade organic reactions.