Dendrimer-encapsulated Pd nanoparticles as catalysts for C-C cross-couplings in flow microreactors

The inner walls of glass microreactors were functionalized with dendrimer-encapsulated Pd nanoparticles. The catalysts were efficient for the Heck-Cassar (copper-free Sonogashira) and Suzuki-Miyaura (SMC) cross-coupling reactions. For the Heck-Cassar reaction between iodobenzene and phenylacetylene, the catalytic system exhibited a high turnover frequency (TOF) and on average required milder reaction conditions as compared to other continuous flow cross-couplings. A study of the substituent effect of para-substituted aryl halides revealed a beneficial effect of electron-withdrawing side groups for the SMC. Moreover, a reaction constant (rho) of 1.5, determined from the Hammett plot, indicated a possible rate-determining step other than the oxidative addition.