Preparation and Characterization of a Formally Ni IV –Oxo Complex with a Triplet Ground State and Application in Oxidation Reactions
Preparation and Characterization of a Formally Ni IV –Oxo Complex with a Triplet Ground State and Application in Oxidation Reactions
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具有三重基态的形式 Ni IV -Oxo 配合物的制备和表征及其在氧化反应中的应用
DOI：
10.1021/jacs.2c10196
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发表时间：
2022
影响因子：
15
通讯作者：
Nam, Wonwoo
中科院分区：
文献类型：
--
作者：
Karmalkar, Deepika G.;Larson, Virginia A.;Malik, Deesha D.;Lee, Yong-Min;Seo, Mi Sook;Kim, Jin;Vasiliauskas, Dovydas;Shearer, Jason;Lehnert, Nicolai;Nam, Wonwoo
高价的第一排过渡金属-氧代配合物是有机分子的生物和化学相关氧化转化以及（人工）光合作用中的水裂解反应中的重要中间体。虽然高价的Fe-和Mn-氧代配合物已被详细表征，但对其与后过渡金属的类似物知之甚少。在这项研究中，我们提出了一个独特的单核终端镍-O配合物的合成和详细的表征。这种化合物，[Ni（TAML）（O）（OH）]3-，其特征在于在730 nm附近的强电荷转移（CT）带，并且具有aSt = 1基态，如通过磁性圆二色性光谱测定的。由扩展X射线吸收精细结构（EXAFS）计算得到Ni-O键长为1.84 μ m。Ni-K边XAS数据表明配合物中含有一个Ni（III）中心，这是由于Ni-O π键的反转程度异常大，其中一个空穴位于氧代配体上.因此，该配合物最好被描述为低自旋Ni（III）配合物（S = 1/2）与束缚的oxyl（O·-）配体（S= 1/2），其中Ni和oxyl的自旋是铁磁耦合的，从而产生了基态的xenvedSt = 1。这种成键描述大致相当于Ni-O单键（σ）的存在。反应性研究表明，[Ni（TAML）（O）（OH）]3-是一种强氧化剂，能够氧化苯硫醚和苯乙烯衍生物，Hammett图中的负ρ值很大，表明其亲电性。该中间体在烃的C-H键活化中也显示出高反应性，在氧杂蒽氧化中具有7.0（3）的动力学同位素效应。
High-valent first-row transition-metal–oxo complexes are important intermediates in biologically and chemically relevant oxidative transformations of organic molecules and in the water splitting reaction in (artificial) photosynthesis. While high-valent Fe– and Mn–oxo complexes have been characterized in detail, much less is known about their analogues with late transition metals. In this study, we present the synthesis and detailed characterization of a unique mononuclear terminal Ni–O complex. This compound, [Ni(TAML)(O)(OH)]3–, is characterized by an intense charge-transfer (CT) band around 730 nm and has anSt= 1 ground state, as determined by magnetic circular dichroism spectroscopy. From extended X-ray absorption fine structure (EXAFS), the Ni–O bond distance is 1.84 Å. Ni K edge XAS data indicate that the complex contains a Ni(III) center, which results from an unusually large degree of Ni–O π-bond inversion, with one hole located on the oxo ligand. The complex is therefore best described as a low-spin Ni(III) complex (S= 1/2) with a bound oxyl (O•–) ligand (S= 1/2), where the spins of Ni and oxyl are ferromagnetically coupled, giving rise to the observedSt= 1 ground state. This bonding description is roughly equivalent to the presence of a Ni–O single (σ) bond. Reactivity studies show that [Ni(TAML)(O)(OH)]3–is a strong oxidant capable of oxidizing thioanisole and styrene derivatives with large negative ρ values in the Hammett plot, indicating its electrophilic nature. The intermediate also shows high reactivity in C–H bond activation of hydrocarbons with a kinetic isotope effect of 7.0(3) in xanthene oxidation.