Mechanistic studies of aliphatic ligand hydroxylation of a copper complex by dioxygen: A model reaction for copper monooxygenases
Mechanistic studies of aliphatic ligand hydroxylation of a copper complex by dioxygen: A model reaction for copper monooxygenases
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DOI：
10.1021/ja972809q
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发表时间：
1998-04-01
影响因子：
15
通讯作者：
Fukuzumi, S
中科院分区：
文献类型：
--
作者：
Itoh, S;Nakao, H;Fukuzumi, S
对三齿配体1a {N，N-双[2-（2-吡啶基）乙基]-2-苯乙胺}的铜配合物中脂族配体被O-2羟基化的机理进行了研究，以阐明我们的铜单加氧酶功能模型的活性氧种类的结构和反应性（Itoh，S.;等，J. Am. 1995，117，4714）。当铜配合物[Cu-II（1a）（ClO 4）（2）]在O-2气氛下用等摩尔量的苯偶姻和三乙胺在CH_2Cl_2中处理时，在配体的苄基位置选择性地发生有效的羟基化，定量地提供含氧产物2a {N，N-双[2（2-吡啶基）乙基]-2-苯基-2-羟基乙胺}。使用O-18（2）的同位素标记实验证实了2a中OH基的氧原子来源于分子氧。用紫外可见光谱、共振拉曼光谱和电子自旋共振（ESR）光谱对[Cu-I（1a）]（+）与O-2反应的研究表明，在反应初期形成的是μ-η（2）：η（2）-过氧二铜（II）配合物。对过氧络合物形成的动力学分析表明，Cu（I）络合物和单体superoxocopper（II）物种的反应是mu-eta（2）：eta（2）-peroxodicopper（II）中间体形成的速率决定因素。当配体1a被1，1，2，2-四氘代苯乙胺衍生物1a-d（4）替代时，对于配体羟基化步骤观察到相对小的动力学氘同位素效应（k（H）/k（D）= 1.8，在-40 ℃）。羟基化反应的速率对配体的对位取代基[（PyCH_2CH_2）（2）NCH_2CH_2Ar，1a Ar = C_6 H_5; 1b Ar = p-CH_3C_6 H_4，1c Ar = p-Cl_6 H_4，1d Ar = p-NO_2C_6 H_4]不敏感，但随溶剂的不同而变化（THF >丙酮> CH_3OH> CH_2Cl_2）。p-取代基、溶剂和动力学氘同位素效应表明，μ-η（2）：η（2）-过氧二铜（II）中间体的O-O键均裂是脂肪族配体羟基化过程中的速率决定步骤。基于动力学和交叉实验的结果，我们提出了一个机制，涉及分子内C-H键活化的双-μ-氧代二铜（III））型中间体的配体羟基化反应。
Mechanistic studies on the aliphatic ligand hydroxylation in a copper complex of tridentate ligand 1a {N,N-bis[2-(2-pyridyl)ethyl]-2-phenylethylamine} by O-2 have been performed in order to shed light on the structure and reactivity of the active oxygen species of our functional model for copper monooxygenases (Itoh, S.; et al. J. Am. Chem. Soc. 1995, 117, 4714). When the copper complex [Cu-II(1a)(ClO4)(2)] was treated with an equimolar amount of benzoin and triethylamine in CH2Cl2 under O-2 atmosphere, efficient hydroxylation occurred selectively at the benzylic position of the ligand to provide oxygenated product 2a {N,N-bis[2(2-pyridyl)ethyl]-2-phenyl-2-hydroxyethylamine} quantitatively. An isotope labeling experiment using O-18(2) confirms that the oxygen atom of the OH group in 2a originates from molecular oxygen. Spectroscopic analyses using UV-vis, resonance Raman, and ESR on the reaction of [Cu-I(1a)](+) and O-2 at low temperature show that a mu-eta(2):eta(2)-peroxodicopper(II) complex is an initially formed intermediate. Kinetic analysis on the peroxo complex formation indicates that the reaction of the Cu(I) complex and the monomeric superoxocopper(II) species is rate-determining for the formation of the mu-eta(2):eta(2)-peroxodicopper(II) intermediate. When ligand 1a is replaced by 1,1,2,2-tetradeuterated phenethylamine derivative 1a-d(4), a relatively small kinetic deuterium isotope effect (k(H)/k(D) = 1.8 at -40 degrees C) is observed for the ligand hydroxylation step. The rate of the hydroxylation step is rather insensitive to the p-substituent of the ligand [(PyCH2CH2)(2)NCH2CH2Ar, 1a Ar = C6H5; 1b Ar = p-CH3C6H4, 1c Ar = p-ClC6H4, and 1d Ar = p-NO2C6H4)], but it varies depending on the solvent (THF > acetone > CH3OH > CH2Cl2). The p-substituent, the solvent, and the kinetic deuterium isotope effects suggest that O-O bond homolysis of the mu-eta(2):eta(2)-peroxodicopper(II) intermediate is involved as a rate-determining step in the aliphatic ligand hydroxylation process. Based on the results of the kinetics and the crossover experiments, we propose a mechanism involving intramolecular C-H bond activation in a bis-mu-oxodicopper(III)) type intermediate for the ligand hydroxylation reaction.