Metal-Organic Framework Node-Supported Single-Site Iron(III)-Hydroxyl Catalyst for Regioselective Hydroxylation of...

Direct and regioselective hydroxylation of arenes remains a significant challenge due to the similar reactivity of multiple C-H bonds, competing electronic and steric effects, and the tendency for nonselective radical pathways under oxidative conditions. In this work, we report a porous aluminum-based metal-organic framework (MOF)-node-supported monoiron(III) dihydroxyl catalyst, DUT-5-Fe(OH)₂, for direct and regioselective arene hydroxylation using H₂O₂ as an oxidant. The heterogeneous and recyclable DUT-5-Fe(OH)₂ catalyst exhibits high catalytic performance, achieving 99% phenol selectivity at 70 °C in the hydroxylation of benzene. Furthermore, DUT-5-Fe(OH)₂ catalyzes the hydroxylation of a broad range of substituted arenes, including heteroarenes such as pyridine and quinoline. Notably, it affords exclusive para-selectivity for monosubstituted arenes, irrespective of the electronic nature of the substituents on the aromatic rings. The high regioselectivity arises from shape-selective catalysis, where the confined pore environment of DUT-5-Fe(OH)₂ prevents overoxidation to hydroquinone or benzoquinone and disfavors sterically hindered ortho- and meta- products. Spectroscopic, kinetic, and computational studies, along with experimental evidence, elucidate the reaction pathway, which reveal that in situ generated ^•OH radicals, mediated by DUT-5-Fe(OH)₂, serve as the key species for benzene hydroxylation. This study demonstrates the utility of MOF-supported single-site earth-abundant metal catalysts for the synthesis of fine chemicals.