Utilizing Charge Effects and Minimizing Intramolecular Proton Rearrangement to Improve the Overpotential of a Thiosemicarbazonato Zinc HER Catalyst
Utilizing Charge Effects and Minimizing Intramolecular Proton Rearrangement to Improve the Overpotential of a Thiosemicarbazonato Zinc HER Catalyst
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DOI：
10.1021/acs.inorgchem.9b01912
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发表时间：
2019-10-07
影响因子：
4.6
通讯作者：
Grapperhaus, Craig A.
中科院分区：
文献类型：
--
作者：
Cronin, Steve P.;Al Mamun, Abdullah;Grapperhaus, Craig A.
合成了二乙酰基-2-（4-甲基-3-缩氨基硫脲）-3-（2-肼基吡啶）锌配合物ZnL 1（1），并评价了其作为均相条件下乙腈中析氢反应（HER）的预催化剂的性能。配合物1在肼基吡啶部分的非配位氮上质子化，在加入乙酸后得到活性催化剂Zn（HL 1）OAc（2）。碘甲烷与1加成，得到相应的甲基化衍生物（ZnLI）-I-2（3）。在溶液中，配位碘化物的部分解离产生阳离子衍生物3 '。配合物1-3通过H-1 NMR、FT-IR和UV-可见光谱进行了表征。通过单晶X射线衍射测定了化合物2和3的固态结构。在乙腈中以乙酸作为质子源进行的HER研究在1.27 V的过电位下1的溶液产生7700 s（-1）的转换频率（TOF），在0.56 V的过电位下3的溶液产生6700 s（-1）的TOF。对于两种络合物，催化所需的电位E-cat/2大于热力学还原电位，E-1/2，表示归因于分子内质子重排的动力学势垒。1（+440 mV）溶液的影响大于3（+160 mV）溶液。控制电位库仑法研究用于确定法拉第效率为71和89%的解决方案1和3，分别。对于这两种催化剂，在催化条件下的电位的广泛循环导致在玻璃碳电极表面上的膜的沉积，其作为HER催化剂是活性的。通过X-射线光电子能谱法分析3的膜表明络合物在沉积时保持完整。一个建议的配体为中心的HER机制与1作为预催化剂2的计算支持使用密度泛函理论（DFT）。采用密度泛函理论（DFT）/B3 LYP/6- 311 g（d，p）方法，采用极化连续模型（PCM）对反应机理中的所有催化中间体进行了结构和能量表征。该机制的热力学可行性支持的平衡常数或还原电位的计算为每个建议的步骤。
The zinc(II) complex of diacetyl-2-(4-methyl-3-thiosemicarbazone)-3-(2-hydrazonepyridine), ZnL1 (1), was prepared and evaluated as a precatalyst for the hydrogen evolution reaction (HER) under homogeneous conditions in acetonitrile. Complex 1 is protonated on the noncoordinating nitrogen of the hydrazonepyridine moiety to yield the active catalyst Zn(HL1)OAc (2) upon addition of acetic acid. Addition of methyl iodide to 1 yields the corresponding methylated derivative (ZnLI)-I-2 (3). In solution, partial dissociation of the coordinated iodide yields the cationic derivative 3'. Complexes 1-3 were characterized by H-1 NMR, FT-IR, and UV-visible spectroscopies. The solid-state structures of 2 and 3 were determined by single crystal X-ray diffraction. HER studies conducted in acetonitrile with acetic acid as the proton source yield a turnover frequency (TOF) of 7700 s(-1) for solutions of 1 at an overpotential of 1.27 V and a TOF of 6700 s(-1) for solutions of 3 at an overpotential of 0.56 V. For both complexes, the required potential for catalysis, E-cat/2, is larger than the thermodynamic reduction potential, E-1/2, indicative of a kinetic barrier attributed to intramolecular proton rearrangement. The effect is larger for solutions of 1 (+440 mV) than for solutions of 3 (+160 mV). Controlled potential coulometry studies were used to determine faradaic efficiencies of 71 and 89% for solutions of 1 and 3, respectively. For both catalysts, extensive cycling of potential under catalytic conditions results in the deposition of a film on the glassy carbon electrode surface that is active as an HER catalyst. Analysis of the film of 3 by X-ray photoelectron spectroscopy indicates the complex remains intact upon deposition. A proposed ligand-centered HER mechanism with 1 as a precatalyst to 2 is supported computationally using density functional theory (DFT). All catalytic intermediates in the mechanism were structurally and energetically characterized with the DFT/B3LYP/6-311g(d,p) in solution phase using a polarizable continuum model (PCM). The thermodynamic feasibility of the mechanism is supported by calculation of equilibrium constants or reduction potentials for each proposed step.