Examination of transmetalation pathways and effects in aqueous Suzuki coupling using biomimetic Pd nanocatalysts

Carbon-carbon (C-C) coupling reactions are ubiquitously used for the generation of advanced chemical species; however, this reactivity remains inefficient and energy intensive. Transitioning such systems toward more sustainable and green conditions would be ideal where Pd nanoparticles represent unique catalysts to achieve this goal. In this contribution, we demonstrate the use of peptide-capped Pd nanoparticles as catalysts for driving Suzuki C-C coupling, focusing specifically on the effects of the transmetalation step in controlling the reactivity. These materials achieved C-C bond formation in water at room temperature using low Pd loadings. Coupling across a variety of mono- and disubstituted substrates was studied, where the reactivity was dependent upon the halogen moiety. Furthermore, studies of the reaction conditions revealed a strong sensitivity to the base identity, suggesting that competing transmetalation pathways and reaction equilibrium effects lead to variations in Suzuki coupling yields. Based on these results, and in comparison to the Stille coupling reactivity of the same materials, it is suggested that the transmetalation step is important in controlling the overall C-C coupling process. This evidence is significant for nanocatalysts to optimize reactivity under sustainable conditions.