The high-valent nickel(iii) complex Ni(pyalk)2 + (2) was prepared by oxidation of a nickel(ii) complex, Ni(pyalk)2 (1) (pyalk = 2-pyridyl-2-propanoate). 2 and derivatives were fully characterized by mass spectrometry and X-ray crystallography. Electron paramagnetic resonance spectroscopy and X-ray photoelectron spectroscopy confirm that the oxidation is metal-centered. 2 was found to react with a variety of phenolic and hydrocarbon substrates. A linear correlation between the measured rate constant and the substrate bond dissociation enthalpy (BDE) was found for both phenolic and hydrocarbon substrates. Large H/D kinetic isotope effects were also observed for both sets of substrates. These results suggest that 2 reacts through concerted proton-electron transfer (CPET). Analysis of measured thermodynamic parameters allows us to calculate a bond dissociation free energy (BDFE) of ∼91 kcal mol-1 for the O-H bond of the bound pyalk ligand. These findings may shed light onto CPET steps in oxidative catalysis and have implications for ligand design in catalytic systems.

中文翻译：

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高价镍络合物对苯酚和碳氢化合物的协同质子电子转移氧化。

高价镍(iii)络合物Ni(pyalk)2 + (2)是通过氧化镍(ii)络合物Ni(pyalk)2 (1)（pyalk = 2-吡啶基-2-丙酸酯）制备的。2 及其衍生物通过质谱和 X 射线晶体学进行了充分表征。电子顺磁共振能谱和X射线光电子能谱证实氧化是以金属为中心的。2被发现能与多种酚类和碳氢化合物底物发生反应。对于酚类和碳氢化合物底物，测得的速率常数与底物键解离焓 (BDE) 之间存在线性相关性。两组底物也观察到大的 H/D 动力学同位素效应。这些结果表明 2 通过协同质子电子转移 (CPET) 进行反应。通过对测量的热力学参数的分析，我们可以计算出结合的 pyalk 配体的 OH 键的键解离自由能 (BDFE) 约为 91 kcal mol-1。这些发现可能揭示氧化催化中的 CPET 步骤，并对催化系统中的配体设计产生影响。