Origin of Unprecedented Formation and Reactivity of Fe IV ═O Species via Oxygen Activation: Role of Noncovalent Interactions and Magnetic Coupling.

Emulating the capabilities of the soluble methane monooxygenase (sMMO) enzymes, which effortlessly activate oxygen at diiron(II) centers to form a reactive diiron(IV) intermediate Q, which then performs the challenging oxidation of methane to methanol, poses a significant challenge. Very recently, one of us reported the mononuclear complex [(cyclam)Fe II (CH 3 CN) 2 ] 2+ ( 1 ), which performed a rare bimolecular activation of the molecule of O 2 to generate two molecules of Fe IV ═O without the requirement of external proton or electron sources, similar to sMMO. In the present study, we employed the density functional theory (DFT) calculations to investigate this unique mechanism of O 2 activation. We show that secondary hydrogen-bonding interactions between ligand N-H groups and O 2 play a vital role in reducing the energy barrier associated with the initial O 2 binding at 1 and O-O bond cleavage to form the Fe IV ═O complex. Further, the unique reactivity of Fe IV ═O species toward simultaneous C-H and O-H bond activation process has been demonstrated. Our study unveils that the nature of the magnetic coupling between the diiron centers is also crucial. Given that the influence of magnetic coupling and noncovalent interactions in catalysis remains largely unexplored, this unexplored realm presents numerous avenues for experimental chemists to develop novel structural and functional analogues of sMMO.