通过碱性钴(I)中心的质子化形成的氢化钴(III)长期以来一直被视为将质子电催化还原为氢的关键中间体。对控制其形成的结构和电子因素的理解是开发更有效和有效的催化剂的关键。Co K边缘X射线吸收光谱,扩展的X射线吸收精细结构,密度泛函理论(DFT)和时变DFT方法的结合已用于研究几种环戊二烯基(Cp)Co(III)L( L =配体)物种及其两电子还原的Co(I)类似物。结果表明,当L强烈接受π时,还原的物质显示出富电子的Co(I)中心与配体L之间的强反向键合,导致弱碱性的Co中心不会质子化形成Co(III)–H。相反,弱的π接受或σ供电的配体系统会导致一个富电子的Co(I)中心,该中心很容易质子化以形成Co(III)–H。这项研究揭示了组合X射线光谱法/理论方法在理解配体在调节电子结构和随后的金属中心反应性中的作用方面的优势。
Electron transfer and chloride ligand dissociation in complexes [(C5Me5)ClM(bpy)]+/[(C5Me5)M(bpy)]n (M=Co, Rh, Ir;n = 2+, +, 0, −): A combined electrochemical and spectroscopic investigation
摘要:
In contrast to the rapid and chemically reversible two-electron ECE' reductive elimination reaction [(C(5)Me(5))ClM(bpy)](+) + 2e(-) --> (C(5)Me(5))M(bpy) + Cl-, M = Rh or Ir, the analogous cobalt system exhibits two separate one-electron steps (EC + E' process) with a persistent, EPR-spectroscopically characterized cobalt(II) intermediate [(C(5)Me(5))Co(bpy)](+). Within the series of coordinatively unsaturated homologous species (C,Me,)M(bpy), the cobalt derivative exhibits the smallest and the iridium homologue the largest metal(I)-to-bpy electron transfer in the ground state, as evident from electrochemical potentials and long-wavelength absorption data. A comparison within that homologous series indicates why the rhodium system, with its intermediate position, is most suitable for hydride transfer catalysis.