Exploring the mechanism of Stille C-C coupling via peptide-capped Pd nanoparticles results in low temperature reagent selectivity

Article abstract of DOI:10.1039/c2cy20636f

Herein we systematically probed the atom-leaching mechanism of Pd nanoparticle-driven Stille coupling to further elucidate the fate of the highly active Pd⁰ atoms released in solution. In this regard, initial oxidative addition at the particle surface results in Pd atom abstraction for reactivity in solution. As a result, two reaction sites are present, the particle surface and pre-leached Pd atoms, thus different degrees of reactivity are possible. This effect was probed via aryl halide combinations that varied the halogen identity allowing for oxidative addition of two substrates simultaneously. The results demonstrate that the system was highly reactive for iodo-based compounds in the mixture at room temperature; however, reactivity at bromo-based substrates was only observed at slightly elevated temperatures of 40.0 °C. As such, substrate selectivity was evident from the catalytic materials that can be controlled based upon the aryl halide composition and reaction temperature. Furthermore, both intermolecular and intramolecular selectivity is possible, thus raising the degree of reaction complexity that can be achieved.