Pd Nanoparticles Decorated by Oxidized Ru Clusters for Efficient C–H/C–H Coupling of Arenes

Oxidative homocoupling of arenes is a challenging but attractive method for converting nonactivated aromatics into biaryl compounds. Applications and the mechanistic understanding of bimetallic nanocatalysts for arene C–H bond activation are limited at present. In this study, we found that a Pd–Ru bimetallic catalyst supported on Al2O3 showed remarkably high catalytic activity for the oxidative homocoupling of arenes owing to the synergistic effect between Pd and Ru. Structural analyses by high-angle annular dark-field scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy and X-ray absorption spectroscopy revealed that the Pd nanoparticles were decorated by partially oxidized Ru clusters. Mechanistic studies indicated that the arene C–H bond cleavage was the rate-determining step and proceeded by a concerted metalation–deprotonation mechanism. It was proposed that the role of Ru is promoting the C–H activation step by generating electron-deficient Pd sites, which was supported by DFT calculations. The Ru-decorated Pd nanoparticles showed large turnover numbers for simple arenes.