Recently, palladium nanoparticles have often been considered responsible for the activity of phosphane-free catalytic systems, especially for C-C coupling processes . It has also been proved that palladium nanoparticles are formed during reduction of the PdCl2(cod) complex under carbonylation reaction conditions .
Three kinds of palladium colloids were prepared by chemical reduction of an aqueous solution of PdCl2 in the presence of PVP as the protecting polymer. Pyrogallol, chromium (II) acetate, and hydrazine were employed as the reducing agents.
All the obtained palladium colloids are characterized by high activity in methoxycarbonylation of iodobenzene. The size and the shape of palladium nanoparticles, as well as the molecular weight of PVP, play the decisive role from the point of view of their catalytic activity .
Oxidative addition of PhI to Pd-PVP as the first step of catalytic reaction was confirmed by TEM and XPS measurements. TEM studies showed a reduction of nanoparticle size after reactions with PhX (X = I, Br) and [Bu4N]X (X = Cl, Br, I). The formation of [Bu4N]2[Pd(Ph)Br3] or [Bu4N]2[PdBr4] type complexes was evidenced by XPS and UV-vis spectra .
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I wish to thank for financial support of my participation in E-MRS Fall Meeting 2006 given from a Nationwide Polish Catalytic Network "Nanomaterials as Catalysts for New, Environmentally Friendly Processes" (AG).