Ramakrishnan Srinivasan, Chakraborty Sumit, Brennessel William W, Chidsey Christopher E D, Jones William D
Department of Chemistry , Stanford University , Stanford , California 94305 , USA . Email:
Department of Chemistry , University of Rochester , Rochester , New York 14627 , USA . Email:
Chem Sci. 2016 Jan 1;7(1):117-127. doi: 10.1039/c5sc03189c. Epub 2015 Oct 29.
A series of square-planar nickel hydride complexes supported by bis(phosphinite) pincer ligands with varying substituents (-OMe, -Me, and -Bu ) on the pincer backbone have been synthesized and completely characterized by NMR spectroscopy, IR spectroscopy, elemental analysis, and X-ray crystallography. Their cyclic voltammograms show irreversible oxidation peaks (peak potentials from 101 to 316 mV Fc/Fc) with peak currents consistent with overall one-electron oxidations. Chemical oxidation by the one-electron oxidant Ce(NBu)(NO) was studied by NMR spectroscopy, which provided quantitative evidence for post-oxidative H evolution leading to a solvent-coordinated nickel(ii) species with the pincer backbone intact. Bulk electrolysis of the unsubstituted nickel hydride () showed an overall one-electron stoichiometry and gas chromatographic analysis of the headspace gas after electrolysis further confirmed stoichiometric production of dihydrogen. Due to the extremely high rate of the post-oxidative chemical process, electrochemical simulations have been used to establish a lower limit of the bimolecular rate constant ( > 10 M s) for the H evolution step. To the best of our knowledge, this is the fastest known oxidative H evolution process observed in transition metal hydrides. Quantum chemical calculations based on DFT indicate that the one-electron oxidation of the nickel hydride complex provides a strong chemical driving force (-90.3 kcal mol) for the production of H at highly oxidizing potentials.
合成了一系列由双（亚膦酸酯）钳形配体支撑的平面正方形镍氢配合物，其钳形主链上带有不同的取代基（-OMe、-Me和-Bu ），并通过核磁共振光谱、红外光谱、元素分析和X射线晶体学对其进行了全面表征。它们的循环伏安图显示出不可逆的氧化峰（峰电位为101至316 mV Fc/Fc），峰电流与整体单电子氧化一致。通过核磁共振光谱研究了单电子氧化剂Ce(NBu)(NO)的化学氧化，这为氧化后氢的析出提供了定量证据，导致形成了钳形主链完整的溶剂配位镍（II）物种。对未取代的镍氢化物（）进行的大量电解显示出整体单电子化学计量比，电解后顶空气体的气相色谱分析进一步证实了化学计量比的氢气生成。由于氧化后化学过程的速率极高，已使用电化学模拟来确定氢析出步骤的双分子速率常数的下限（> 10 M s）。据我们所知，这是在过渡金属氢化物中观察到的已知最快的氧化氢析出过程。基于密度泛函理论的量子化学计算表明，镍氢配合物的单电子氧化为在高氧化电位下生成氢气提供了强大的化学驱动力（-90.3 kcal mol）。
