Trapping an Elusive Fe(IV)-Superoxo Intermediate Inside a Self-Assembled Nanocage in Water at Room Temperature
Rahul Gera, Puja De, Kundan K. Singh, Sergio A. V. Jannuzzi, Aisworika Mohanty, Lucía Velasco, Kulbir kulbir, Pankaj Kumar, José F. Marco, Kalaivanan Nagarajan, Carlos Pecharromán, P. M. Rodriguez‐Pascual, Serena DeBeer, Dooshaye Moonshiram, Sayam Sen Gupta, Jyotishman Dasgupta
Abstract
Molecular cavities that mimic natural metalloenzymes have shown the potential to trap elusive reaction intermediates. Here, we demonstrate the formation of a rare yet stable Fe(IV)-superoxo intermediate at room temperature subsequent to dioxygen binding at the Fe(III) site of a (Et 4 N) 2 [Fe III (Cl)(bTAML)] complex confined inside the hydrophobic interior of a water-soluble Pd 6 L 4 12+ nanocage. Using a combination of electron paramagnetic resonance, Mössbauer, Raman/IR vibrational, X-ray absorption, and emission spectroscopies, we demonstrate that the cage-encapsulated complex has a Fe(IV) oxidation state characterized by a stable S = 1/2 spin state and a short Fe–O bond distance of ∼1.70 Å. We find that the O 2 reaction in confinement is reversible, while the formed Fe(IV)-superoxo complex readily reacts when presented with substrates having weak C–H bonds, highlighting the lability of the O–O bond. We envision that such optimally trapped high-valent superoxos can show new classes of reactivities catalyzing both oxygen atom transfer and C–H bond activation reactions.