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

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