Oxidation mechanism of phenols by dicopper-dioxygen (Cu2/O2) complexes
Oxidation mechanism of phenols by dicopper-dioxygen (Cu2/O2) complexes
复制标题
DOI：
10.1021/ja029380
复制
发表时间：
2003-09-10
影响因子：
15
通讯作者：
Itoh, S
中科院分区：
文献类型：
--
作者：
Osako, T;Ohkubo, K;Itoh, S
本文首次系统研究了中性苯酚（ArOH）被(mu-eta（2):eta(2)-过氧）- diccopper （II）配合物(A)和由2-（2-吡啶基）乙胺三齿配体和双（mu-oxo） diccopper （III）配合物(B)氧化的过程，以深入了解金属-氧类物质对酚类O-H键的激活机制。在这两种情况下（A和B）， C-C偶联二聚体都是在铜-二氧（Cu-2/O-2）配合物的基础上以接近50%的产率获得的唯一可分离产物，这表明A和B都是酚氧化的电子转移氧化剂。Cu-2/O-2配合物氧化苯酚的速率依赖于苯酚底物的单电子氧化电位，以及用ArOD获得的动力学氘同位素效应表明，该反应涉及质子耦合电子转移（PCET）机制。苯酚对cumylperoxyl自由基(C)的净氢原子转移反应的反应活性也进行了研究，表明反应对苯酚单电子氧化电位的速率依赖性明显小于与Cu2O2配合物的反应，表明了直接氢原子转移机制（HAT）。因此，结果明确地证实了Cu2O2配合物对酚的氧化是通过PCET机制进行的，而不是通过cumylperoxyl自由基体系中的HAT机制进行的。考虑到A和B之间存在的快速平衡，讨论了A和B之间的反应性差异。
The first systematic studies on the oxidation of neutral phenols (ArOH) by the (mu-eta(2):eta(2)-peroxo)-dicopper(II) complex (A) and the bis(mu-oxo)dicopper(III) complex (B) supported by the 2-(2-pyridyl)ethylamine tridentate and didentate ligands L-Py2 and L-Py1, respectively, have been carried out in order to get insight into the phenolic O-H bond activation mechanism by metal-oxo species. In both cases (A and B), the C-C coupling dimer was obtained as a solely isolable product in similar to50% yield base on the dicopper-dioxygen (Cu-2/O-2) complexes, suggesting that both A and B act as electron-transfer oxidants for the phenol oxidation. The rate-dependence in the oxidation of phenols by the Cu-2/O-2 complexes on the one-electron oxidation potentials of the phenol substrates as well as the kinetic deuterium isotope effects obtained using ArOD have indicated that the reaction involves a proton-coupled electron transfer (PCET) mechanism. The reactivity of phenols for net hydrogen atom transfer reactions to cumylperoxyl radical (C) has also been investigated to demonstrate that the rate-dependence of the reaction on the one-electron oxidation potentials of the phenols is significantly smaller than that of the reaction with the Cu2O2 complexes, indicative of the direct hydrogen atom transfer mechanism (HAT). Thus, the results unambiguously confirmed that the oxidation of phenols by the Cu2O2 complex proceeds via the PCET mechanism rather than the HAT mechanism involved in the cumylperoxyl radical system. The reactivity difference between A and B has also been discussed by taking account of the existed fast equilibrium between A and B.