Wang Zhijie, Zhang Haoyan, Zhang Peng, Di Kai, Zhao Jinfeng, Wang Baomin, Qu Jingping, Ye Shengfa, Yang Dawei
State Key Laboratory of Fine Chemicals, Frontier Science Center for Smart Materials, Dalian University of Technology, Dalian 116024, P. R. China.
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, P. R. China.
J Am Chem Soc. 2024 Jul 24;146(29):19737-19747. doi: 10.1021/jacs.4c01691. Epub 2024 Jul 15.
Nitrosobenzene (PhNO) and phenylhydroxylamine (PhNHOH) are of paramount importance because of their involvement as crucial intermediates in the biological metabolism and catalytic transformation of nitrobenzene (PhNO) to aniline (PhNH). However, a complete reductive transformation cycle of PhNO to PhNH via the PhNHOH intermediate has not been reported yet. In this context, we design and construct a new thiolate-bridged dicobalt scaffold that can accomplish coordination activation and reductive transformation of PhNO. Notably, an unprecedented reversible ligand-based redox sequence PhNO ↔ PhNO ↔ PhNO can be achieved on this well-defined {Co(μ-SPh)Co} functional platform. Further detailed reactivity investigations demonstrate that the PhNO and PhNO complexes cannot react with the usual hydrogen and hydride donors to afford the corresponding phenylhydroxylamino (PhNHO) species. However, the double reduced PhNO complex can readily undergo N-protonation with an uncommon weak proton donor PhSH to selectively yield a stable dicobalt PhNHO bridged complex with a high p value of 13-16. Cyclic voltammetry shows that there are two successive reduction events at = -0.075 V and = -1.08 V for the PhNO complex, which allows us to determine both bond dissociation energy (BDE) of 59-63 kcal·mol and thermodynamic hydricity (Δ) of 71-75 kcal·mol of the PhNHO complex. Both values indicate that the PhNO complex is not a potent hydrogen abstractor and the PhNO complex is not an efficient hydride acceptor. In the presence of BH as a combination of protons and electrons, facile N-O bond cleavage of the coordinated PhNHO group can be realized to generate PhNH and a dicobalt hydroxide-bridged complex. Overall, we present the first stepwise reductive sequence, PhNO ↔ PhNO ↔ PhNO ↔ PhNHO → PhNH.
亚硝基苯（PhNO）和苯胲（PhNHOH）至关重要，因为它们作为关键中间体参与了硝基苯（PhNO₂）向苯胺（PhNH₂）的生物代谢和催化转化过程。然而，尚未有通过PhNHOH中间体将PhNO₂完全还原转化为PhNH₂的报道。在此背景下，我们设计并构建了一种新的硫醇盐桥连双钴支架，它能够实现PhNO₂的配位活化和还原转化。值得注意的是，在这个明确的{Co(μ-SPh)Co}功能平台上，可以实现前所未有的基于配体的可逆氧化还原序列PhNO₂↔PhNO↔PhNO。进一步详细的反应性研究表明，PhNO₂和PhNO配合物不能与常见的氢和氢化物供体反应生成相应的苯胲（PhNHO）物种。然而，双还原的PhNO配合物可以很容易地与一种不常见的弱质子供体PhSH进行N-质子化反应，选择性地生成一种稳定的双钴PhNHO桥连配合物，其pKa值高达13 - 16。循环伏安法表明，PhNO₂配合物在E₁/₂ = -0.075 V和E₁/₂ = -1.08 V处有两个连续的还原事件，这使我们能够确定PhNHO配合物的键解离能（BDE）为59 - 63 kcal·mol⁻¹，热力学氢负离子亲和力（ΔG°H）为71 - 75 kcal·mol⁻¹。这两个值都表明PhNO₂配合物不是一种有效的氢原子提取剂，PhNO配合物也不是一种有效的氢化物受体。在存在BH₄⁻作为质子和电子的组合时，可以实现配位的PhNHO基团的N - O键的轻松断裂，生成PhNH₂和一种双钴氢氧化桥连配合物。总体而言，我们展示了第一步逐步还原序列，即PhNO₂↔PhNO↔PhNO↔PhNHO→PhNH₂。
