Heterogenizing palladium tetraiodide catalyst for carbonylation reactions

We report the first example of successful heterogenization of the classical PdI carbonylation catalyst, achieved in two simple steps from ionic liquid-functionalized multi-walled carbon nanotubes (MWCNTs). The newly developed materials (PdI@MWCNT-imi-X, X = Br, I) present the PdI anion supported on an imidazolium network (imi) grown on MWCNTs and have been fully characterized. The activity of PdI@MWCNT-imi-X has been successfully tested in a paradigmatic carbonylation reaction, the oxidative monoaminocarbonylation of 1-alkynes with amines to give high value added 2-ynamides (obtained in good yields, 50-84%, starting from various substrates). The heterogeneous catalyst could be easily recycled and showed a good efficiency even after the fourth recycle, when deactivation began to occur owing to the formation of inactive Pd(0) species, as confirmed by XPS analysis. Hot and cold filtration tests were compatible with an essentially heterogeneous catalytic process, and limited metal contamination in the final organic compounds occurred, as assessed by ICP-MS analysis of representative carbonylation products.