The Role of Pd Nanoparticles in Ionic Liquid in the Heck Reaction

Abstract
Pd(0) nanoparticles with ∼2 nm diameter, immobilized in 1-n-butyl-3-methylimidazolium hexafluorophosphate ionic liquid, are efficient catalyst precursors for coupling of aryl halides with n-butylacrylate. In situ TEM analysis of the ionic liquid catalytic solution after the catalytic reaction shows the formation of larger nanoparticles (∼6 nm). The palladium content in the organic phase during the arylation reaction was checked by ICP-AS and shows significant metal leaching (up 34%) from the ionic phase to the organic phase at low substrate conversions and drops to 5−8% leaching at higher conversions. These results strongly suggest that the Pd(0) nanoparticles serve as a reservoir of “homogeneous” catalytic active species.

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