Novel Heterogeneous Pd Catalysts for Cross-Coupling Reactions in Biocompatible Media: Structural Insights from Solid-State NMR Techniques

Abstract Novel SBA-15-supported heterogeneous catalysts are synthesized and applied in the Mizoroki?Heck and the Suzuki?Miyaura cross-coupling reactions in green solvents like PEG or water. The structural properties of the products after each synthesis step are monitored by different analytics. The amount of amine/carboxyl groups and vanillin/histidine methyl ester and thermal stability are determined by TGA and elemental analysis, while ICP-OES delivered the amount of palladium of the catalysts. The morphology is investigated by SEM and XPS and confirms the presence of coordinated palladium in the zero-oxidation state. Gas adsorption analysis is conducted, which indicates the presence of palladium clusters in one of the two catalysts, which is underlined by BSE images combined with EDX. A detailed 13C ssNMR and DNP-enhanced 15N ssNMR spectral analysis is presented, which provides ultimate proof of the successful syntheses of the catalysts. The coordination of the palladium onto the carrier material is shown by combining the NMR spectral results with the results of the other analytics. First catalytic tests show for the Mizoroki?Heck reaction yields up to nearly 100% and for the Suzuki-Miyaura up to 88% in the presence of PEG and water, respectively.