Oxidative Addition of Aryl Halides to Palladium(0) Complexes: A Density-Functional Study Including Solvation

Using density-functional theory calculations in combination with an electrostatic continuum
solvation model, we have investigated the oxidative addition of phenyl halides PhX to
palladium(0) complexes of bidentate phosphanes [Pd(PP)], yielding aryl halo complexes [(PP)Pd(Ph)(X)], with X = Cl, Br, I and PP = 1,2-bis(dimethylphosphino)ethane or (P)-2,2‘-bis(dimethylphosphino)-1,1‘-biphenyl. We have considered the formation of the reactive 14-electron species from the saturated [Pd(PP)2] as well as different prereaction complexes
[(PP)Pd(PhX)] with an intact phenyl halide. We find that ligand dissociation is the limiting
reaction step, while the formation of the prereaction complex and the oxidative addition
itself are energetically (very) favorable. The concerted transition state for oxidative addition
known in the gas phase could not be found in solution. Instead, we propose a pathway
involving the very facile dissociation of the halide from the prereaction complex, with
subsequent collapse to the product.