2 Computational details
All of our calculations were conducted with the Gaussian 09 software20. The geometry optimization of all the complexes were performed at the M06 level 21, and the basis set lanL2DZ22 was used for Pd and Cl and 6-31g(d)23for other atoms. Polarization functions24 were added for Pd with ζf= 1.472 and Cl withζd = 0.640 in the calculation. Frequencies for all reported structures at the same level of theory were analytically computed to confirm all the stationary points as minima (zero imaginary frequency), or transition states (only one imaginary frequency). An intrinsic reaction coordinate (IRC) 25analysis was carried out to identify that transition states smoothly connect two relevant minima. To consider the effects of solvent, single-point energy calculations for all the species were obtained using a self-consistent reaction field (SCRF) method based on the polarizable continuum model (PCM) 26 at a higher level of M06/6-311++G (d, p) (SDD 27 basis set for Pd and Cl atoms), using 1,4-dioxane as solvent corresponding to the experimental conditions. The M06 functional28 has been confirmed to provide accurate energy calculations for organic transition metal systems 29-34. And the natural population analysis (NPA) charge calculations were carried out for selected systems35.