The reversal of regioselectivity in a Pd-catalyzed cross-coupling reaction of an aryl chloro triflate with different ligands, established by FU and co-workers, has been Studied computationally. C-O insertion was found to be controlled by Pd-HOMO ArO-LUMO interaction, where C-Cl insertion is facilitated by the lower C-Cl TS distortion energy. The greater reactivities of monoligated Pd species are due primarily to the lack of distortion of the Pd species.