Güell Mireia, Luis Josep M, Solà Miquel, Siegbahn Per E M
Departament de Química, Institut de Química Computacional, Universitat de Girona, Campus de Montilivi, 17071, Girona, Spain.
J Biol Inorg Chem. 2009 Feb;14(2):229-42. doi: 10.1007/s00775-008-0443-y. Epub 2008 Oct 30.
Tyrosinase catalyzes the ortho hydroxylation of monophenols and the subsequent oxidation of the diphenolic products to the resulting quinones. In efforts to create biomimetic copper complexes that can oxidize C-H bonds, Stack and coworkers recently reported a synthetic mu-eta(2):eta(2)-peroxodicopper(II)(DBED)(2) complex (DBED is N,N'-di-tert-butylethylenediamine), which rapidly hydroxylates phenolates. A reactive intermediate consistent with a bis-mu-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 was studied with hybrid density functional methods by replacing DBED in the mu-eta(2):eta(2)-peroxodicopper(II)(DBED)(2) complex by N,N'-dimethylethylenediamine ligands 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)O(2)-derived species.
酪氨酸酶催化单酚的邻位羟基化反应以及随后二酚产物氧化生成相应的醌。为了制备能够氧化C-H键的仿生铜配合物，斯塔克及其同事最近报道了一种合成的μ-η(2):η(2)-过氧二铜(II)(DBED)₂配合物（DBED为N,N'-二叔丁基乙二胺），该配合物能迅速使酚盐羟基化。实验观察到一种与双μ-氧代-二铜(III)-酚盐配合物一致的反应中间体，其O-O键完全断裂。总体而言，该合成配合物中O-O键依次断裂和C-O键形成的证据表明，对于酪氨酸酶催化的酚羟基化反应通常所接受的协同或后期O-O键断裂机制，存在另一种替代机制。在这项工作中，通过用N,N'-二甲基乙二胺配体取代μ-η(2):η(2)-过氧二铜(II)(DBED)₂配合物中的DBED，以降低计算成本，采用杂化密度泛函方法研究了该过氧二铜(II)配合物的反应机理。将得到的反应机理与现有的关于单酚催化邻位羟基化以及随后二酚产物氧化生成醌的提议进行比较，旨在对由2:1 Cu(I)O₂衍生物种介导的铜促进氧化过程有所了解。
