Pd nanoparticle and molecular Pd2+ leaching pathways for a strongly acid versus strongly basic resin supported Pd nanoparticle catalyst in Suzuki coupling.

• The leaching behaviour and mechanisms are elucidated via combined data analysis. • A homogeneous-heterogeneous catalytic system prevails for both NP catalysts. • The leaching pathway critically depends on the resin functionality. • Phenylpalladium(II)hydroxide complexes are proposed as the leached Pd2+ species. The Pd leaching behaviour of a strongly acid (Lewatit K2629) versus strongly basic (Lewatit MP500 OH) ion exchange resin supported Pd nanoparticle (Pd-NP) catalyst is elucidated in the Suzuki reaction between iodobenzene and phenylboronic acid with K 2 CO 3 as base in 1:1 (v/v) DMF/H 2 O at 40 °C. Reaction and leaching kinetic analyses combined with hot filtration tests indicated heterogeneous-homogeneous catalysis for both Pd-NP catalysts. More particularly, leaching experiments showed that for Pd-NP Lewatit K2629, Pd-NP as well as molecular Pd2+ leaching (as phenylpalladium(II)hydroxide complexes) occurred due to, respectively, the disturbance of the electrostatic NP stabilization by dissociated K 2 CO 3 and reaction with iodobenzene and hydroxide. For Pd-NP Lewatit MP500 OH, however, molecular Pd2+ leaching induced by iodobenzene, dominates. Hence, the resin functionality determines the contribution of each leaching pathway. Furthermore, at high conversions, Pd re-deposition occurred due to the decreased amount of leaching inducing reagents causing enlarged NPs in the resin which leached less in subsequent runs. [ABSTRACT FROM AUTHOR]