Theoretical Investigations into C-H Bond Activation Reaction by Nonheme Mn(IV)O Complexes: Multistate Reactivity with No Oxygen Rebound

Recently published experimental results on a nonheme synthetic [(Bn-TPEN)(MnO)-O-IV](2+) complex reveal that it is capable of activating strong C-H bonds. However, the final products are shown to contain Mn-III instead of the expected Mn-II, which should be formed if a rebound mechanism similar to what is assumed for heme (FeO)-O-IV was to occur. It was proposed that the substrate radical generated during H-abstraction dissociates from the (MnOH)-O-III complex and undergoes an additional reaction to a second molecule of (MnO)-O-IV, leading to Mn-III. Density functional calculations reveal the root cause of why a follow-up rebound to form Mn-II and alcohol is not preferred in this system. It is further shown that nonheme (MnO)-O-IV has a more complex spin-state manifold during C-H activation reactions compared with (FeO)-O-IV, and that spin-state matters in oxidative chemistry of metal-oxo reagents.