Investigation of activity, stability, and degradation mechanism of surface-supported Pd-PEPPSI complexes for Suzuki-Miyaura coupling

Abstract Secure surface-molecule linkages are critical to designing recyclable surface-supported molecular catalysts. A series of N-heterocyclic carbene (NHC)-functionalized Pd-PEPPSI complexes are tethered using different linker chemistries to polymer and silica supports and examined for their reactivity in Suzuki-Miyaura cross-coupling reactions. Attachment chemistries investigated include tetrazine-norbornene cycloaddition click chemistry onto a polystyrene bead, incorporation via ring-opening metathesis polymerization (ROMP) into a poly(norbornene) polymer, and immobilization onto silica gel via silyl ether linkage. Palladium black formation suggests that the catalysts become detached from the support, and soluble palladium particles are the catalytically active species. These results help probe the manner in which the pyridine ligand of the PEPPSI complex helps to stabilize the catalysts and ultimately, how the catalysts fail. Further, we highlight the interplay between catalyst stability, recyclability, and reliable surface linkages.