Origins of Substituent, Ligand, and Counterion Effects in a Ruthenium-Catalyzed Aromatization-Driven C-C Bond Cleavage.

Density functional theory (DFT) calculations were performed to elucidate the reaction mechanism of a ruthenium-catalyzed aromatization-driven C-C bond cleavage and to rationalize the experimentally observed trends in product selectivity, substituent-controlled reactivity, ligand dependence, and counterion effects. β-Carbon elimination is identified as the turnover-limiting step, governing both reactivity and product selectivity. Substituent-dependent selectivities are qualitatively reproduced: ESP and ETS-EDA analyses highlight electrostatic and transition-state interactions for alkyl substrates, while LOL-π reveals π-stabilization responsible for selectivity reversal in aryl systems. To clarify the origin of substituent-controlled reactivity, CDA analysis shows that increasing substitution progressively perturbs the balance between metal-substrate donation and back-donation, which elevates the β-carbon elimination barrier and thereby reduces catalytic efficiency. Ligand effects are found to arise from a multidimensional interplay among P-Ru-P bite angles, effective steric confinement, transition-state distortion, and ligand-to-Ru donation, rather than from any single geometric or electronic descriptor. Finally, distortion-interaction and LOL analyses demonstrate that the pronounced counterion effect originates primarily from excessive geometric distortion and reduced transition-state stabilization in the PF6--assisted pathway, explaining the dramatic suppression of catalytic activity relative to OTf-.