Mechanistic Insights Into Dirhodium‐Catalyzed Arylation of sp ² C─H Bond: Reaction Profile, Ligand Effects, and Comparison With Diruthenium Catalysis

This study uses systematic density functional theory calculations to elucidate the mechanism of dirhodium/NHC‐catalyzed C─H arylation. In the Rh ₂ (OAc) ₄ /NHC system, C─H activation follows a stepwise pathway that involves oxidative addition to a Rh(I) center followed by acetate‐assisted deprotonation. The significantly higher reactivity of IMes compared to IPr is attributed to the prohibitively high C─H activation barrier (41.0 kcal  mol ⁻¹ ) for IPr, consistent with experimental observations. Comparative analysis with the Ru ₂ (OAc) ₄ Cl/PCy ₃ system reveals a divergent mechanism: In the Ru system, C─H activation proceeds via a concerted metalation–deprotonation pathway, in which the Ru─Ru bond is cleaved, and the two metal centers are bridged by a chloride ion in all key transition states; in contrast, in the Rh system, the Rh─Rh bond remains intact during C─H activation and oxidative addition. Crucially, the ligand environment, particularly the chloride ion in the Ru system, stabilizes a halide‐bridged dinuclear geometry that in turn affects the preferred oxidation states and the overall reaction pathway. This work provides a molecular‐level understanding of bimetallic cooperation and establishes a theoretical foundation for the rational design of dinuclear C─H functionalization catalysts.