Theoretical study of the hydroxylation of phenolates by the Cu2O2(N,N'-dimethylethylendiamine)22+ complex

Abstract

Tyrosinase catalyses the ortho-hydroxylation of monophenol and the subsequent oxidation of the diphenolic product to the resulting quinone. In efforts to create biomimetic copper complexes that can oxidize C-H bonds, Stack and coworkers recently reported a synthetic -2:2-peroxodicopper(II)(DBED)2 complex (DBED = N,N'-di-tert-butylethylendiamine), which rapidly hydroxylates phenolates. A reactive intermediate consistent with a bis--oxo-dicopper(III)-phenolate complex, with the O-O bond fully cleaved, is observed experimentally. Overall, the evidence for sequential O O bond cleavage and C-O bond formation in this synthetic complex suggests an alternative mechanism to the concerted or late stage O-O bond scission generally accepted for the phenol hydroxylation reaction performed by tyrosinase. In this work, the reaction mechanism of this peroxodicopper(II) complex has been studied with hybrid density functional methods by replacing DBED in the -2:2-peroxodicopper(II)(DBED)2 complex by DMED ligands (DMED = N,N'-dimethylethylendiamine) to reduce the computational costs. The reaction mechanism obtained is compared with the existing proposals for the catalytic ortho-hydroxylation of monophenol and the subsequent oxidation of the diphenolic product to the resulting quinone with the aim of gaining some understanding about the copper-promoted oxidation processes mediated by 2:1 Cu(I)O2-derived species