Dynamical Mechanism May Avoid High-Oxidation State Ir(V)-H Intermediate and Coordination Complex in Alkane and Arene C-H Activation by Cationic Ir(III) Phosphine

Organometallic reaction mechanisms are assumed to be appropriately described by minimum energy pathways mapped out by density functional theory calculations. For the two-step oxidative addition/reductive elimination mechanism for C-H activation of methane and benzene by cationic Cp*(PMe3)Ir-III(CH3), we report quasiclassical direct dynamics simulations that demonstrate the Ir-v-H intermediate is bypassed in a significant amount of productive trajectories initiated from vibrationally averaged velocity distributions of oxidative addition transition states. This organometallic dynamical mechanism is akin to the sigma-bond metathesis pathway but occurs on the oxidative addition/reductive elimination energy surface and blurs the line between two- and one-step mechanisms. Quasiclassical trajectories also reveal that the momentum of crossing the reductive elimination structure always induces complete alkane and arene dissociation from the Ir metal center, skipping weak C-H sigma and pi coordination complexes. This suggests that these weak coordination complexes after reductive elimination are not necessarily on the reaction pathway and likely result from a solvent cage.