Leaching of palladium atoms from small cluster models during Heck reactions – An experimental and theoretical study.

Relevant parameters for the leaching of palladium atoms from small Pd clusters during Heck reactions of bromobenzene and styrene have been explored computationally and experimentally. With density functional theory calculations, we modeled reaction free energies for removing a Pd atom from a Pd 6 model cluster and for forming Pd-ligand complexes. Oxidative addition of bromobenzene decreases the dissolution energy. Additional parameters and mechanisms, especially bromide ions render the leaching process notably exergonic. Model results exhibit the same trends as the targeted experiments where Pd leaching from supported catalysts (Pd/C, Pd/SiO 2) was monitored as function of reaction temperature, time and components. [Display omitted] • Direct correlation of palladium leaching with reaction rate of Heck coupling. • Quantification of Pd dissolution as function of temperature, time and composition. • Aryl halide, alkene and bromide favor leaching singly and in combination. • Qualitative agreement of DFT model simulations with closely targeted experiments. [ABSTRACT FROM AUTHOR]