Ligand-free ultrasmall palladium nanoparticle catalysis for the Mizoroki-Heck reaction in aqueous micelles

Despite the wide utility of micellar palladium (Pd) nanoparticle (NP)-catalyzed Mizoroki-Heck reactions in laboratory and industrial synthesis, the easy construction of micellar Pd NPs and the detailed role of surfactants remain the focus of attention. Here, we present a simple and sustainable strategy to construct a nanoreactor by connecting micelles with Pd NPs. This strategy enables us to obtain ultrasmall Pd NPs with an average particle size of 1.8 nm, mainly in situ synthesized by triethylamine (Et3N) reduction and stabilized by chelating with sugar-based surfactant micelles. The first-order kinetic model related to the initial concentration of Pd-based catalyst is established, and the apparent activation energy of this reaction in aqueous micellar solutions is calculated to be 40.49 kJ mol-1. The mechanism of the active species ultrasmall Pd(0) NPs obtained by the reductive elimination of Pd(ii) precursors by base was demonstrated. Notably, the recycled aqueous reaction mixture containing the micelles and Pd NPs can be reused. A simple and sustainable strategy is proposed to construct a nanoreactor by connecting micelles with in-situ prepared ultrasmall Pd NPs to efficiently catalyze the Mizoroki-Heck reaction.