Dendrimer-encapsulated palladium nanoparticles for continuous-flow Suzuki-Miyaura cross-coupling reactions

Generation three, four, and five (G3, G4, and G5) poly(amidoamine) dendrimers were used for the encapsulation of palladium nanoparticles (Pd NPs) and their covalent anchoring within glass microreactors. G3-encapsulated Pd NPs showed the highest activity for a model Suzuki-Miyaura cross-coupling (SMC) reaction of the three different encapsulated Pd NPs tested, as compared to G4 and G5. A kinetic study indicated a role of the nanoparticle as a procatalyst, from which molecular species are formed with an induction time of approximately 1 min. The dendrimer-nanoparticle catalytic platform exhibited excellent reactivity (high turnover frequencies and numbers) compared to other Pd NP flow reactors and dendrimer-encapsulated Pd NPs at batch scale. Moreover, the Pd microreactor exhibited good stability, as witnessed by running the SMC reaction for more than 7 days with a low Pd leaching of 1.2 ppm. The covalently attached dendrimers may play a crucial role in stabilizing the Pd NPs, a critical feature in flow SMC reactions.