Spedalotto Giuseppe, Lovisari Marta, McDonald Aidan R
School of Chemistry, Trinity College Dublin, The University of Dublin, College Green, Dublin 2, Ireland.
ACS Omega. 2021 Oct 15;6(42):28162-28170. doi: 10.1021/acsomega.1c04225. eCollection 2021 Oct 26.
Despite their potential role in enzymatic systems, there is a dearth of hydroxide-bridged high-valent oxidants. We recently reported the synthesis and characterization of NiNi(μ-OH) () and Ni (μ-OH) () species supported by a dicarboxamidate ligand (,'-bis(2,6-dimethyl-phenyl)-2,2-dimethylmalonamide). Herein, we explore the oxidative reactivity of these species using a series of para-substituted 2,6-di--butyl-phenols (4-X-2,6-DTBP, X = -OCH, -CHCH, -CH, -C(CH), -H, -Br, -CN, and -NO) as a mechanistic probe. Interestingly, upon reaction of with the substrates, the formation of a new transient species, was observed. is postulated to be a protic congener of . All three species were demonstrated to react with the substituted phenols through a hydrogen atom transfer reaction mechanism, which was elucidated further by analysis of the postreaction mixtures. Critically, was demonstrated to react at far superior rates to and , and oxidized substrates more efficiently than any bis-μ-oxo-Ni reported to date. The kinetic superiority of with respect to and was attributed to a stronger bond in the product of oxidation by when compared to those calculated for and .
尽管它们在酶系统中可能发挥作用，但氢氧化物桥连的高价氧化剂却很匮乏。我们最近报道了由二羧酰胺配体（N,N'-双(2,6-二甲基苯基)-2,2-二甲基丙二酰胺）支撑的NiNi(μ-OH)()和Ni(μ-OH)()物种的合成与表征。在此，我们使用一系列对取代的2,6-二叔丁基苯酚（4-X-2,6-DTBP，X = -OCH₃、-CH₂CH₃、-CH₃、-C(CH₃)₃、-H、-Br、-CN和-NO₂）作为机理探针，探索这些物种的氧化反应活性。有趣的是，在与底物反应时，观察到形成了一种新的瞬态物种。据推测是 的质子类似物。所有这三种物种都被证明通过氢原子转移反应机理与取代苯酚发生反应，通过对反应后混合物的分析进一步阐明了该机理。至关重要的是，已证明 与 和 的反应速率要高得多，并且比迄今报道的任何双-μ-氧代-Ni 更有效地氧化底物。 相对于 和 的动力学优势归因于 氧化产物中的键比 和 计算得出的键更强。
