Real-time fluorescence imaging of a heterogeneously catalysed Suzuki–Miyaura reaction

The palladium-catalysed Suzuki–Miyaura reaction is one of the most important methods for C–C cross-coupling, yet the heterogeneous version of this reaction remains poorly understood. More specifically, the question of whether the reaction occurs on the surface of the catalyst (heterogeneous process) or is promoted by leaching of palladium species in solution (homogeneous phase) is still under debate. Here, we use real-time high spatial resolution microscopy to monitor a palladium-catalysed coupling reaction that produces a highly fluorescent BODIPY dye. We show catalyst migration during the reaction, which we attribute to a dissolution/redeposition mechanism where migrating palladium species become true active sites after attachment to the catalyst support. The observed process is heterogeneous, but the active catalysts (atoms or small clusters) have important mobility, as revealed by the observation of migrating catalytic sites. Our report shows the strength of single-molecule studies for unveiling fundamental mechanisms in heterogeneously catalysed reactions that are otherwise difficult to explore with classical ensemble experiments. There has been a long-standing debate on whether heterogeneously catalysed Suzuki cross-couplings can occur homogeneously due to metal leaching. Here the authors show that while the palladium from the nanoparticle catalyst is mobile during the reaction, the active sites remain heterogeneous in nature.