Divergent Mechanisms in Iridium/Rhodium‐Catalyzed Carbene Generation from Sulfoxonium Ylides: A Density Functional Theory Study

A computational study has been performed to investigate the mechanisms of both the iridium-catalyzed amidocarbonylation of olefins and the CH bond activation using sulfoxonium ylide as a carbene precursor. For the iridium-catalyzed amidocarbonylation of olefins, the optimal mechanism involves deprotonation, migratory insertion of the olefin, carbenation, carbene insertion, and protonation, with protonation identified as the rate-determining step. Conversely, Ir-catalyzed CH activation proceeds through CH bond activation, carbenation, carbene insertion, and protonation, where CH bond activation constitutes the rate-determining step. Computational result further reveals that Rh-catalyzed amidocarbonylation of olefins exhibits a higher activation barrier (25.7 kcal mol^-1), with carbenation as the rate-limiting step, sharply contrasting with the iridium-catalyzed system. The second-order perturbation theory analysis (SOPT) reveals significant charge delocalization between lone-pair electrons, bonding (BD), and antibonding (BD*) orbitals. This electronic delocalization rationalizes the observed energy disparities during Ir- versus Rh-carbene formation. Supporting this, natural bond orbital charge analysis of carbenation transition states confirms a lower activation barrier for Ir-carbene formation compared to Rh-carbene formation.