Selective hydroxylation of benzene to phenol via CuII(μ-O˙)CuII intermediate using a nonsymmetric dicopper catalyst

Abstract

The one-step oxidation of benzene to phenol represents a significant and promising advancement in modern industries focused on the production of high-value-added chemical products. Nevertheless, challenges persist in achieving sufficient catalytic selectivity and preventing over-oxidation. Inspired by copper enzymes, we present a nonsymmetric dicopper complex ([Cu^II₂(TPMAN)(μ-OH)(H₂O)]³⁺, 1) for the selective oxidation of benzene to phenol. Utilizing H₂O₂ as the oxidant, complex 1 demonstrates remarkable catalytic activity (a TON of 14 000 within 29 hours) and selectivity exceeding 97%, comparable to the finest homogeneous catalyst derived from first-row transition metals. It is noteworthy that the significant substituent effect, alongside a negligible kinetic isotope effect (KIE = 1.05), radical trapping experiments, and an inconsistent standard selectivity test of the ˙OH radicals, all contradict the conventional Fenton mechanism and rebound pathway. Theoretical investigations indicate that the active Cu^II(μ-O˙)Cu^II–OH species generated through the cleavage of the O–O bond in the Cu^II(μ-1,1-OOH)Cu^I intermediate facilitates the hydroxylation of benzene via an electrophilic attack mechanism. The nonsymmetric coordination geometry is crucial in activating H₂O₂ and in the process of O–O bond cleavage.