Stabilization of Palladium Catalysts for the Heck Reaction by Support Functionalization and Solvent Selection

Abstract

Pd nanoparticles were synthesized on nonfunctionalized and functionalized SBA‐15 grafted with thiol or amine groups. The resulting materials were used as catalysts to study the influence of these functional groups for a similar Pd particle size of approximately 2 nm on the Heck reaction that uses iodide substrates. The nonfunctionalized catalysts lost their activity quickly because of Pd leaching and particle growth. However, if a mixed solvent that consisted of toluene and DMF was used and thiol groups were grafted on SBA‐15, we were able to reduce the Pd leaching and particle growth to thus obtain a more stable catalyst in which an important role of the ligands was to recapture Pd. However, heterogeneity tests, such as a hot filtration test and poisoning experiments, gave a strong indication that Pd still leached from the support and that homogeneous Pd species were mainly responsible for the activity. Pd on S‐functionalized SBA‐15 was able to catalyze the Heck reaction using different substrates to achieve good activity and selectivity in most cases.

Current advances in the utility of functionalized SBA mesoporous silica for developing encapsulated nanocatalysts: state of the art

“…One of the most important advances in this eld is developing hybrid systems through functionalization of mesoporous silica materials. [51][52][53][54][55][56] In this context using sulfur, [57][58][59][60][61][62] phosphorous and amine-based functional groups 63,64 has attracted growing attention and resulted in introducing novel hybrid systems [65][66][67][68] with outstanding utilities for catalysis.…”

Pd Nanoparticles Immobilized on Graphene Oxide/Silica Nanocomposite: Efficient and Recyclable Catalysts for Cross‐Coupling Reactions

“…The Pd nanoparticles were immobilized on N‐ or S‐ functionalized GO using a modified method described by de Jong et al . By this protocol the solid support is capable of removing Pd species from solution.…”

“…Some authors report that functional groups, such as thiol and amine groups, grafted on ordered mesoporous silica and fumed silica are able to reduce Pd leaching in Heck and Suzuki reactions . Shimizu et al .…”

Pd nanoparticles confined in mesoporous N-doped carbon silica supports: a synergistic effect between catalyst and support

“…Previous reports have indicated that during the Suzuki reaction, leached Pd species formed during catalysis are of considerable importance for the conversion of reactants to Catalysis Science & Technology Paper products, thus, the actual catalytic species are in solution. 57,[63][64][65][66][67] However, this is a controversial subject because other authors have reported that C-C coupling reactions take place preferentially on the metal particle surface, thus in a heterogeneous fashion. 56,[68][69][70] We used the PVP test to investigate the leaching process.…”