Homeopathic Heck reaction

Scheme 1.5 Mechanism proposed by de Vries [31 n] for the homeopathic Heck reaction between phenyl iodide and butyl acrylate catalyzed by Pd(OAc)2 [31c-f, l-o]. Reprinted with permission from Ref [31 n].

Scheme 7.7 Homeopathic, phosphine ligand-free palladium catalyst in Mizoroki-Heck reactions.

TON increases when the amount of nanoparticle catalyst is decreased or when the solution is diluted. The efficiency reaches 54% yield using 1 ppm Pd nanoparticles, i.e. the amount of nanoparticle catalyst is homeopathic. On the other hand, with high loading of catalyst, the yield is not quantitative, reaching only 70% at 1% Pd atom catalyst. These phenomena are taken into account by a leaching mechanism whereby one or two Pd atoms escape from the nanoparticle surface subsequent to the oxidative addition of the aryl halide onto the nanoparticle surface, then become extremely active in solution until it is quenched by the mother nanoparticle [66]. A similar mechanism had been proposed earlier by de Vries for the Heck reaction at high temperature (150-170°C) [67-69],... 

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