Theoretical Insights into Rhodium-Catalyzed Kumada−Tamao−Corriu Coupling: Multifunctional Roles of a Pincer Aluminyl Ligand

RhI(PAlP), a rhodium(I) complex bearing a pincer aluminyl ligand (PAlP) incorporating an anionic AlN2 unit, exhibits high catalytic activity toward the Kumada−Tamao−Corriu (KTC) cross-coupling of fluorobenzene with diphenylmagnesium Mg(Ph)2. In this study, density functional theory calculations were performed to elucidate the reaction mechanism, revealing an unusual catalytic cycle enabled by the multifunctional roles of the aluminyl ligand. The reaction is initiated by C(sp2)−F σ-bond activation at the Rh and Al sites of RhI(PAlP), affording a rhodium(I) phenyl intermediate in which the anionic AlN2 unit is converted into a neutral AlN2F ligand. Subsequent reaction with Mg(Ph)2 proceeds via an oxidative transmetalation, generating a RhIII(PAlP)(Ph)2 species that undergoes reductive elimination to produce biphenyl. Reductive elimination is identified as the rate-determining step, with a moderate Gibbs activation free energy (ΔG‡ = 19.5 kcal mol−1) consistent with the experimentally observed catalytic activity. Notably, in contrast to conventional transmetalation processes that preserve the oxidation state of the transition metal, the rhodium center is oxidized from +I to +III during this step. Strong Al−F and Mg−F interactions suppress phenyl migration to aluminum and instead promote phenyl coordination to rhodium, concomitant with Mg−F bond formation and regeneration of the anionic aluminyl ligand. These cooperative interactions collectively enable the oxidative transmetalation mechanism. In addition, the present study predicts that RhI(PAlP) is catalytically competent for the Negishi coupling but inactive toward the Suzuki−Miyaura coupling under base-free conditions. Taken together, these findings underscore the distinctive catalytic reactivity imparted by the pincer aluminyl ligand.