text: In 1955, S. Winstein and T. G. Traylor published a study of the mechanism of acetolysis of organomercury compounds. They propose a series of possible mechanisms for the process, which they rule out through based on their kinetic data. A concerted metalation deprotonation is considered, and they are unable to rule it out through the data they collect. 
  The metalation of organic C–H bonds was extended from mercury to palladium in 1968 by J. M. Davidson and C. Triggs who identified that palladium acetate reacts with benzene in perchloric acid and acetic acid to give biphenyl, palladium(0), and 2 equivalents of acetic acid through an organopalladium intermediate. Early mechanistic studies found that palladium acetate was the best palladium precatalyst due to the presence of the acetate ligand. Mechanistic investigation has been ongoing since these initial discoveries, and infrared spectroscopy on the picosecond–millisecond time scale was used in 2021 to observe the states involved in proton transfer from acetic acid to a metalated ligand, which is the microscopic reverse of a concerted metalation deprotonation process.