Aromatic C−H Hydroxylation Reactions with Hydrogen Peroxide Catalyzed by Bulky Manganese Complexes

The oxidation of aromatic substrates to phenols with H2O2 as a benign oxidant remains an ongoing challenge in synthetic chemistry. Herein, we successfully achieved catalyze C−H bond oxidations using series biologically inspired manganese catalysts fluorinated alcohol solvents. While introduction bulky substituents into the ligand structure catalyst favors alkylbenzenes, occurs at benzylic position ligands bearing electron-rich substituents. Therefore, nature is key controlling chemoselectivity these Mn-catalyzed oxidations. We show that groups prevents inhibition through phenolate-binding, consequently providing higher catalytic turnover numbers for phenol formation. Furthermore, employing halogenated carboxylic acids presence provides enhanced activities, which can be attributed their low pKa values reduces by phenolate protonation well electron-withdrawing character makes oxo species more electrophilic oxidant. Moreover, best our knowledge, new system accomplish alkylbenzenes highest yields so far reported homogeneous arene hydroxylation catalysts. Overall data provide proof-of-concept how Mn(II)/H2O2/RCO2H systems are easily tunable means solvent, acid additive, and steric demand ligand. chemo- site-selectivity patterns current system, negligible KIE, observation NIH-shift, effectiveness tBuOOH overall suggest bonds proceeds metal-based mechanism, no significant involvement hydroxyl radicals, via oxide intermediate.