Title : Heck catalysis of palladium nanoparticles obtained in different reducing systems
Palladium(0) nanoparticles have been widely used in cross coupling reactions, including Heck reactions. For this study, we obtained palladium(0) nanoparticles in colloidal suspension using different combinations of solvents and reducing methods under aerobic conditions. The variation in systems used to synthesize palladium(0) nanoparticles resulted in different nanoparticle sizes. To investigate whether the particle size had an effect on catalysis, we used two different temperature and reaction times as reaction conditions, without the use of stabilizing agents, other than the solvent and/or the anions in the initial nanoparticle synthesis. All of the palladium nanoparticles investigated, worked in the cross coupling C-C Heck reaction, but yields did not show appreciable differences when high temperature and long reaction times promote a high reduction of palladium(II). With the use of lower temperature and reaction time, the differences start to be observed. The best C-C catalysis conversion was observed when N,N-dimethylformamide was used as solvent in the absence of reducing agent and with sodium citrate as reducing agent. The obtained size of the nanoparticles act as a reservoir of soluble palladium species that behave as the true catalyst.