Exploring the Mechanism of Biomimetic Arene Hydroxylation: When a Diiron Metal Center Meets a Sulfur-Containing Ligand

Efficient and selective arene hydroxylation under mild reaction conditions is a challenging task in chemical transformation. To achieve this goal, one of us recently reported an experimental breakthrough of a highly efficient iron catalyst based on the sulfur-containing ligand BCPOM. However, the exact mechanism underlying this promising biomimetic catalysis remained elusive. Herein, based on density functional theory modelings combined with experimental results, we successfully revealed an unexpected mechanism of this biomimetic arene hydroxylation. In this mechanism of diiron/BCPOM, the disulfide group of the ligand was found to assist the O–O cleavage of the peroxo species by concomitantly forming an S–O bond, which thus generated an uncommon diferric diiron-oxo intermediate as the real oxidant for the subsequent arene hydroxylation. In this way, the revealed hydroxylation mechanism with diiron/BCPOM differs not only from the mononuclear heme enzyme P450 but also from the diiron nonheme enzyme T4MO substantially. Consistent with the NIH shift experimental results, this mechanism also enabled the experimentally confirmed regioselectivity prediction for some substrates unexplored previously. The unexpected role played by the sulfur-containing ligand in assisting the O–O cleavage by forming the S–O bond further expands our knowledge on how sulfur can facilitate the iron-catalyzed reactions.