A Pd–Cu bimetallic system was not discovered until 2006 when Goossen et al. reported a decarboxylative cross-coupling of aryl halides with ortho-substituted aromatic carboxylic acids.
Through subsequent studies it was found that the use of aryl triflates allowed substrate scope for cross-coupling to be extended to some aromatic carboxylates lacking any ortho-substitution (less reactive). This was a result of the fact that any halide anion generated in the reaction inhibited the Cu-catalyzed decarboxylation process.
Further optimization of the system and catalyst conditions has made decarboxylative cross-coupling using bimetallic Pd–Cu systems applicable to organic synthesis, most predominantly in the formation of biaryls.
As well, the variability of this combined catalytic system allows for promotion of a large spectrum of reactions, including aryl ketone formation, c-heteroatom cross-coupling, and many others.