Molecular Palladium Catalysts Supported on Functionalized Oxide Surfaces

Surface-bound, molecular single-site palladium catalysts were achieved through grafting of dimethylpalladium(II) complexes on dehydroxylated silica. IR, NMR and EXAFS spectroscopy as well as elemental analysis confirmed the successful synthesis. The properties of the surface complexes such as stability and reactivity were investigated by temperature-programmed reactions and revealed that the behavior of the metal centers is strongly dependent on the backbone ligand bound to Pd. EXAFS studies showed that small Pd(0) cluster can be generated by defined thermal and reductive treatments, which are the result of the movement of the originally isolated metal centers. CO atmosphere significantly enhances the palladium mobility. The palladium surface complexes were applied as catalysts to Heck reactions and showed superior activity compared to conventional catalysts regarding the ability to activate C-Cl bonds. Extensive leaching studies yielded fundamental insights in the palladium dissolution mechanism and dynamics dependent on pre-catalyst and substrates.

Through covalent bonding of silanes with varying organic substituents on silica surfaces, properties such as polarity were modified. Suitable substituents and reaction conditions for this surface functionalization were evaluated.