Wacker Oxidation of Terminal Alkenes Over ZrO2 -Supported Pd Nanoparticles Under Acid- and Cocatalyst-Free Conditions

Abstract

Highly efficient Wacker oxidation of aromatic or aliphatic terminal alkenes into methyl ketones and benzofurans is developed by using reusable Pd⁰ nanoparticles (NPs) supported on ZrO₂ under acid- and cocatalyst-free conditions. Molecular oxygen or air can be utilized as the terminal oxidant, which results in the formation of H₂ O as the only theoretical byproduct. The activation of the Pd NPs by O₂ plays an important role in promoting this reaction. Interestingly, PdO supported on ZrO₂ showed no activity. Additionally, the Pd particle size significantly affects the catalytic activity, with an apparent optimal diameter of 4-12 nm. In addition to the heterogeneous catalyst forms, the Pd NPs can be generated from a Pd⁰ complex during the reaction, and these particles are even recyclable.

Keywords: alkenes; heterogeneous catalysis; oxidation; palladium; size effect.