Surface catalysed Suzuki-Miyaura cross-coupling by Pd nanoparticles: an operando XAS study

Area of Science:

• Heterogeneous catalysis
• Nanoparticle synthesis and characterization
• Organometallic chemistry

Background:

• Palladium nanoparticles are crucial catalysts for cross-coupling reactions like the Suzuki coupling.
• Understanding the stability and active sites of nanoparticles under reaction conditions is vital for catalyst design.
• Distinguishing between heterogeneous and homogeneous catalytic pathways is a persistent challenge in palladium catalysis.

Purpose of the Study:

• To investigate the stability and catalytic behavior of polyvinylpyrrolidone (PVP)-stabilized palladium (Pd) nanoparticles during Suzuki cross-coupling.
• To elucidate the role of nanoparticle surface defects in the catalytic cycle using operando X-ray absorption spectroscopy (XAS).
• To evaluate the effectiveness of chemical and structural poisons in differentiating heterogeneous from homogeneous contributions in Pd-catalyzed reactions.

Main Methods:

• Operando liquid phase X-ray absorption spectroscopy (XAS) was employed to study PVP-stabilized Pd nanoparticles.
• The Suzuki cross-coupling reaction between iodonanisole and phenylboronic acid was performed in a MeOH-toluene solvent mixture with KOMe base.
• Selective chemical and structural poisons were utilized to probe the catalytic mechanisms.

Main Results:

• XAS analysis confirmed the stability of palladium nanoparticles, showing no significant metal leaching throughout the Suzuki coupling reaction.
• Surface defect sites on the palladium nanoparticles were identified as directly involved in the catalytic cycle.
• The study explored the efficacy of various poisons in distinguishing heterogeneous and homogeneous catalytic contributions.

Conclusions:

• PVP-stabilized palladium nanoparticles exhibit excellent stability under Suzuki cross-coupling conditions.
• Surface defects play a critical role in the catalytic activity of these nanoparticles.
• The findings provide insights into the mechanisms of heterogeneous palladium catalysis and methods for mechanistic elucidation.