带有 N2P2 型配体的四配位方形平面 Ni(II)配合物的电化学制氢技术

IF 3.2 Q2 CHEMISTRY, PHYSICAL
Energy advances Pub Date : 2024-08-09 DOI:10.1039/D4YA00345D
Hidenori Miyake, Satomi Hirasawa, Yurika Uno, Kenichi Nakao, Takuma Kato, Yuko Wasada-Tsutsui, Yoshikuni Hara, Tomohiro Ozawa, Tomohiko Inomata and Hideki Masuda
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引用次数: 0

摘要

制备了一种含有 N2P2- 型配体 [Ni(LH)2](BF4)2(LH = 2-((二苯基膦)甲基)-吡啶)的镍(II)配合物,并对其进行了结构、光谱和电化学表征。研究了它的电化学制氢反应,并与之前报道的配体中含有氨基的 Ni(II) 复合物[Ni(LNH2)2](BF4)2(LNH2 = 6-((二苯基膦)甲基)-吡啶-2-胺)进行了比较。X 射线晶体结构显示,该化合物为顺式四配位方形平面结构(τ4 = 0.25),反阴离子 BF4- 弱地呈现在 Ni(II) 离子上。根据 UV-vis 和 NMR 光谱特征评估了溶液中的结构,结果显示在二氯甲烷中为四配位方平面结构,在乙腈中为与溶剂分子结合的五配位或六配位结构。以 AcOH 为质子源的电化学制氢反应与 [Ni(LNH2)2](BF4)2 的表现相似,催化电流(icat)与添加的 AcOH 浓度的平方根成正比。这表明反应机理是 EECC,决定速率的步骤是双电子还原的 Ni(0) 物种与接近的质子反应形成 Ni(II)-Hー 物种的阶段。在与之前研究相同的条件下(复合物:1 mM,电解质 [n-Bu4N](ClO4):0.1 M in MeCN (3 mL),AcOH = 145 equiv.(在 MeCN 中 pKa = 22.3))时,TOF 和电位值分别为 1060 s-1 和 710 mV。与[Ni(LNH2)2](BF4)2(TOF 8800 s-1,过电位 430 mV)相比,这些数值在过电位方面更高,在 TOF 方面更小。通过 DFT 计算评估了起始材料 [NiII(LH)2]2+ 的结构和氢化物 Ni(II) 复合物 [NiIIH(LH)2]+ 的形成,后者是氢进化反应的一个反应中间体。根据这两种络合物的氢演化行为结果,可以清楚地证明氨基在氢生成反应中作为质子转移位点起着重要作用。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Electrochemical hydrogen generation by a four-coordinate square-planar Ni(ii) complex with an N2P2-type ligand†

Electrochemical hydrogen generation by a four-coordinate square-planar Ni(ii) complex with an N2P2-type ligand†

A Ni(II) complex with an N2P2-type ligand, [Ni(LH)2](BF4)2 (LH = 2-((diphenylphosphino)methyl)-pyridine), was prepared and characterized structurally, spectroscopically, and electrochemically. Its electrochemical hydrogen production capability was investigated and compared with that of a previously reported Ni(II) complex bearing an amino group in the ligand, [Ni(LNH2)2](BF4)2 (LNH2 = 6-((diphenylphosphino)methyl)-pyridin-2-amine). The X-ray crystal structure was revealed to be a four-coordinate square planar structure (τ4 = 0.25) in the cis form, with the counter anion BF4 weakly coordinated to the Ni(II) ion. The structure in the solution was assessed on the basis of UV-vis and NMR spectral features, which showed a four coordinate square planar structure in dichloromethane and a five- or six-coordinate structure bound with solvent molecules in acetonitrile. The electrochemical hydrogen production reaction using AcOH as a proton source showed a similar behaviour to that of [Ni(LNH2)2](BF4)2, with the catalytic current (icat) proportional to the square root of the concentration of AcOH added. This indicates that the reaction mechanism is EECC and that the rate-determining step is the reaction of the two-electron reduced Ni(0) species with the approaching proton to form the Ni(II)–H species. The TOF and overpotential values, when evaluated under the same conditions as in a previous study (complex: 1 mM, electrolyte [n-Bu4N](ClO4): 0.1 M in MeCN (3 mL), AcOH = 145 equiv. (pKa = 22.3 in MeCN)), were found to be 1060 s−1 and 710 mV, respectively. These values were higher for the overpotential and smaller for TOF, as compared to those of [Ni(LNH2)2](BF4)2 (TOF 8800 s−1, overpotential 430 mV). The structure of the starting material [NiII(LH)2]2+ and the formation of the hydride Ni(II) complex [NiII(LH)2H]+, a reaction intermediate in the hydrogen evolution reaction, were evaluated by DFT calculations. The results of the hydrogen evolution behaviour of these two complexes show that the electron-donating amino group plays an important role in the hydrogen evolution reaction, not only capturing protons but also increasing the basicity of the pyridyl N atom.

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