Origin of Protonation Side Products in Pd-Catalyzed Decarboxylative Allylation Reactions: Evidence for In Situ Modification of Triphenylphosphine Ligand

Palladium-catalyzed decarboxylative allylation (DcA) is a well-established method of carbon-carbon bond formation. This type of coupling is quite attractive, as the only byproduct is CO2. While a wide variety of ligands have been employed with Pd(0) or Pd(II) precatalysts in DcA reactions, the ligand structure is most often based on a triarylphosphine core. Despite their demonstrated utility, DcA processes have been hindered by the formation of protonation side products. While this phenomenon has been widely acknowledged, little has been reported on the origin of the proton. Herein, we address this and provide multiple lines of experimental evidence for the proton originating from the triarylphosphine ligand.