Detailed density functional theory calculations provide valuable insight into reactivity-controlling factors in transition metal-catalyzed C-H activation by carboxylate assistance. The chelation-Assisted activation of a variety of arenes by 3d and 4d transition metal complexes was analyzed by means of bond order analysis through density functional theory (DFT) calculations as well as energy decomposition analysis through DLPNO-CCSD(T) calculations, thereby providing in-depth information on distinct electronic influences on the key C-H activation transition state and demonstrating a preferred activation through a base-Assisted internal electrophilic substitution (BIES) rather than a concerted metalation-deprotonation (CMD) pathway. Copyright © 2020 American Chemical Society.