The Suzuki-Miyaura cross-coupling reaction of ArX (I, Br) with Ar¢B(OH) 2 , catalyzed by Pd-containing water-soluble micelle formed by PS-PEO copolymer and N-cetylpyridinium chloride as a surfactant, was studied in water and methanol. The reaction was performed under mild conditions (temperature up to 50°C) and the catalyst can be recycled (5 runs) by ultrafiltration without any loss of its catalytic activity. The phenomenon was observed, consisting in growing Pd-nanoparticle size because the small nanoparticles dissolve to form larger nanoparticles in the course of reaction as well as in the presence of the only reagent, ArI. In the latter case, additionally, the formation of very small, not completely dissolved Pd nanoparticles, obviously having a high catalyst activity, is observed. This observation, together with the catalyst activity data might have an implication for a leaching mechanism for the studied catalytic system.
Palladium nanoparticles stabilized in micelles formed by polystyrene-co-poly(ethylene oxide) and cetylpyridinium chloride as a surfactant were investigated as a catalyst in the following reactions: the Heck reaction of 2-ethylhexyl acrylate with iodobenzene and p-bromoacetophenone and heterocyclization of N-methylsulfonyl-o-iodoaniline with phenylacetylene and of methyl o-iodobenzoate with diphenylacetylene leading to formation of substituted indole and isocoumarin, respectively. The activity of the colloidal palladium catalytic system is comparable to that of the low-molecular-weight palladium complexes, whereas the stability of the colloidal palladium system is much higher. The reuse of the catalyst was demonstrated in the experiments with fresh starts as well as by thermomorphous separation of the catalyst from products.
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