Itoh S, Kumei H, Nagatomo S, Kitagawa T, Fukuzumi S
Contribution from the Department of Chemistry, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan.
J Am Chem Soc. 2001 Mar 14;123(10):2165-75. doi: 10.1021/ja0036110.
Phenolate and phenoxyl radical complexes of a series of alkaline earth metal ions as well as monovalent cations such as Na+ and K+ have been prepared by using 2,4-di-tert-butyl-6-(1,4,7,10-tetraoxa-13-aza-cyclopentadec-13-ylmethyl)phenol (L1H) and 2,4-di-tert-butyl-6-(1,4,7,10,13-pentaoxa-16-aza-cyclooctadec-16-ylmethyl)phenol (L2H) to examine the effects of the cations on the structure, physicochemical properties and redox reactivity of the phenolate and phenoxyl radical complexes. Crystal structures of the Mg2+- and Ca2+-complexes of L1- as well as the Ca2+- and Sr2+-complexes of L2- were determined by X-ray crystallographic analysis, showing that the crown ether rings in the Ca2+-complexes are significantly distorted from planarity, whereas those in the Mg2+- and Sr2+-complexes are fairly flat. The spectral features (UV-vis) as well as the redox potentials of the phenolate complexes are also influenced by the metal ions, depending on the Lewis acidity of the metal ions. The phenoxyl radical complexes are successfully generated in situ by the oxidation of the phenolate complexes with (NH4)(2)[Ce4+(NO3)6] (CAN). They exhibited strong absorption bands around 400 nm together with a broad one around 600-900 nm, the latter of which is also affected by the metal ions. The phenoxyl radical-metal complexes are characterized by resonance Raman, ESI-MS, and ESR spectra, and the metal ion effects on those spectroscopic features are also discussed. Stability and reactivity of the phenoxyl radical-metal complexes are significantly different, depending on the type of metal ions. The disproportionation of the phenoxyl radicals is significantly retarded by the electronic repulsion between the metal cation and a generated organic cation (Ln+), leading to stabilization of the radicals. On the other hand, divalent cations decelerate the rate of hydrogen atom abstraction from 10-methyl-9,10-dihydroacridine (AcrH2) and its 9-substituted derivatives (AcrHR) by the phenoxyl radicals. On the basis of primary kinetic deuterium isotope effects and energetic consideration of the electron-transfer step from AcrH2 to the phenoxyl radical-metal complexes, we propose that the hydrogen atom abstraction by the phenoxyl radical-alkaline earth metal complexes proceeds via electron transfer followed by proton transfer.
通过使用2,4 - 二叔丁基 - 6 - (1,4,7,10 - 四氧杂 - 13 - 氮杂环十五 - 13 - 基甲基)苯酚(L1H)和2,4 - 二叔丁基 - 6 - (1,4,7,10,13 - 五氧杂 - 16 - 氮杂环十八 - 16 - 基甲基)苯酚(L2H)，制备了一系列碱土金属离子以及单价阳离子如Na⁺和K⁺的酚盐和苯氧自由基配合物，以研究阳离子对酚盐和苯氧自由基配合物的结构、物理化学性质和氧化还原反应活性的影响。通过X射线晶体学分析确定了L1⁻的Mg²⁺和Ca²⁺配合物以及L2⁻的Ca²⁺和Sr²⁺配合物的晶体结构，结果表明Ca²⁺配合物中的冠醚环明显偏离平面，而Mg²⁺和Sr²⁺配合物中的冠醚环相当扁平。酚盐配合物的光谱特征(紫外 - 可见)以及氧化还原电位也受金属离子影响，这取决于金属离子的路易斯酸度。通过用(NH₄)₂Ce⁴⁺(NO₃)₆氧化酚盐配合物原位成功生成了苯氧自由基配合物。它们在400 nm左右表现出强吸收带以及在600 - 900 nm左右有一个宽吸收带，后者也受金属离子影响。通过共振拉曼光谱、电喷雾电离质谱和电子自旋共振光谱对苯氧自由基 - 金属配合物进行了表征，并讨论了金属离子对这些光谱特征的影响。苯氧自由基 - 金属配合物的稳定性和反应活性根据金属离子的类型有显著差异。金属阳离子与生成的有机阳离子(Lⁿ⁺)之间的电子排斥显著阻碍了苯氧自由基的歧化反应，从而使自由基得以稳定。另一方面，二价阳离子减缓了苯氧自由基从10 - 甲基 - 9,10 - 二氢吖啶(AcrH₂)及其9 - 取代衍生物(AcrHR)夺取氢原子的速率。基于一级动力学氘同位素效应以及对从AcrH₂到苯氧自由基 - 金属配合物的电子转移步骤的能量考虑，我们提出苯氧自由基 - 碱土金属配合物夺取氢原子是通过电子转移随后质子转移的方式进行的。
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