Structural, spectroscopic, and electrochemical properties of tri- and tetradentate N3 and N3S copper complexes with mixed benzimidazole/thioether donors
作者:Ivan Castillo、Víctor M. Ugalde-Saldívar、Laura A. Rodríguez Solano、Brenda N. Sánchez Eguía、Erica Zeglio、Ebbe Nordlander
DOI:10.1039/c2dt30756a
日期:——
Cupric and cuprous complexes of bis(2-methylbenzimidazolyl)(2-methylthiophene)amine (L1), bis(2-methylbenzimidazolyl)benzylamine (L2), bis(2-methylbenzimidazolyl)(2,4-dimethylphenylthioethyl)amine (L3), bis(1-methyl-2-methylbenzimidazolyl)benzylamine (Me2L2), and bis(1-methyl-2-methylbenzimidazolyl)(2,4-dimethylphenylthioethyl)amine (Me2L3) have been spectroscopically, structurally, and electrochemically characterised. The thioether-containing ligands L3 and Me2L3 give rise to complexes with Cu–S bonds in solution and in the solid state, as evidenced by UV-vis spectroscopy and X-ray crystallography. The Cu2+ complexes [L1CuCl2] (1), [L2CuCl2] (2) and [Me2L3CuCl]ClO4 (3Me,ClO4) are monomeric in solution according to ESI mass spectrometry data, as well as in the solid state. Their Cu+ analogues [L1Cu]ClO4, [L2Cu]ClO4, [L3Cu]ClO4 (4–6), [BOC2L1Cu(NCCH3)]ClO4 (4BOC), [Me2L2Cu(NCCH3)2]PF6 (5Me) and [Me2L3Cu]2(ClO4)2 (6Me) are also monomeric in acetonitrile solution, as confirmed crystallographically for 4BOC and 5Me. In contrast, 6Me is dimeric in the solid state, with the thioether group of one of the ligands bound to a symmetry-related Cu+ ion. Cyclic voltammetry studies revealed that the bis(2-methylbenzimidazolyl)amine-Cu2+/Cu+ systems possess half-wave potentials in the range −0.16 to −0.08 V (referenced to the ferrocenium–ferrocene couple); these values are nearly 0.23 V less negative than those reported for related bis(picolyl)amine-derived ligands. Based on these observations, the N3 or N3S donor set of the benzimidazole-derived ligands is analogous to previously reported chelating systems, but the electronic environment they provide is unique, and may have relevance to histidine and methionine-containing metalloenzymes. This is also reflected in the reactivity of [Me2L2Cu(NCCH3)2]+ (5Me) and [Me2L3Cu]+ (6Me) towards dioxygen, which results in the production of the superoxide anion in both cases. The thioether-bound Cu+ centre in 6Me appears to be more selective in the generation of O2˙− than 5Me, lending evidence to the hypothesis of the modulating properties of thioether ligands in Cu–O2 reactions.
双(2-甲基苯并咪唑基)(2-甲基噻吩)胺(L1)、双(2-甲基苯并咪唑基)苄胺(L2)、双(2-甲基苯并咪唑基)(2,4-二甲基苯硫基乙基)胺(L3)的铜和亚铜络合物,双(1-甲基-2-甲基苯并咪唑基)苯甲胺 (Me2L2) 和双(1-甲基-2-甲基苯并咪唑基)(2,4-二甲基苯硫基乙基)胺 (Me2L3) 已进行光谱、结构和电化学表征。紫外-可见光谱和 X 射线晶体学证明,含硫醚的配体 L3 和 Me2L3 在溶液和固态下均可生成具有 Cu-S 键的络合物。根据 ESI 质谱数据,Cu2+ 络合物 [L1CuCl2] (1)、[L2CuCl2] (2) 和 [Me2L3CuCl]ClO4 (3Me,ClO4) 在溶液中以及固态下都是单体。它们的 Cu+ 类似物 [L1Cu]ClO4、[L2Cu]ClO4、[L3Cu]ClO4 (4–6)、[BOC2L1Cu(NCCH3)]ClO4 (4BOC)、[Me2L2Cu(NCCH3)2]PF6 (5Me) 和 [Me2L3Cu]2 (ClO4)2 (6Me) 在乙腈溶液中也是单体,正如 4BOC 和 5Me 的晶体学所证实的那样。相比之下,6Me 是固态二聚体,其中一个配体的硫醚基团与对称相关的 Cu+ 离子结合。循环伏安研究表明,双(2-甲基苯并咪唑基)胺-Cu2+/Cu+体系的半波电位范围为-0.16至-0.08 V(参考二茂铁-二茂铁电偶);这些值比相关双(吡啶甲基)胺衍生配体报道的负值低近 0.23 V。基于这些观察,苯并咪唑衍生配体的 N3 或 N3S 供体组类似于之前报道的螯合系统,但它们提供的电子环境是独特的,并且可能与含组氨酸和蛋氨酸的金属酶有关。这也反映在 [Me2L2Cu(NCCH3)2]+ (5Me) 和 [Me2L3Cu]+ (6Me) 对分子氧的反应性上,这两种情况都会产生超氧阴离子。 6Me 中与硫醚结合的 Cu+ 中心似乎比 5Me 更有选择性地生成 O2˙−,这为硫醚配体在 Cu-O2 反应中的调节特性的假设提供了证据。