Heck reaction aqueous palladium catalysis

The first studies that intentionally used colloidal nanocatalysts were reported independently by Beller et al. [50] and Reetz et al. [51] using chemical reduction and electrochemical techniques, respectively, to synthesize colloidal palladium nanoparticles for the Heck reaction. Both Beller and Reetz concluded that the solution-phase catalysis occurred on the surface of the nanoparticle, without confirming that a homogeneous catalytic pathway was nonexistent. Le Bars et al. [52] demonstrated an inverse relationship between the size of Pd nanoparticles and the TOF (normalized to the total number of surface atoms) for the Heck reaction (Fig. 18.4a). After normalizing the rate to the density of defect sites (for each nanoparticle size) (Fig. 18.4b), the TOF for all particle sizes was identical. Colloidal PVP-capped palladium nanoparticles synthesized by ethanol reduction are effective catalysts for Suzuki cross-coupling reactions in aqueous solution [53]. The El-Sayed group reported that the initial rate of reaction increased linearly with the concentration of Pd nanoparticles [53] and the catalytic activity was inversely proportional to the... 

Reviews on palladium(n) chemistry include one on the formation of its polyamine complexes in aqueous solution.190 A volume of reviews on organopalladium chemistry puts special emphasis on the catalysis of C-C bond forming processes known as the Heck reaction.191... 

Apart from palladium, nickel is also known to catalyse Heck vinylations [9-12]. A supported nickel catalyst was appUed for the Heck reaction of iodobenzene with butyl acrylate [13]. The supported aqueous-phase catalysis performed almost as well as the analogous homogeneous catalyst NiCl2(PPli3)2-Only the conversion was sHghtly lower. No leaching of metal into the product phase was observed (detection limit approx. 1 ppm). The immobihzed catalyst was successfully recycled three times without observing loss of activity and selectivity. 

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