Transient Formation and Reactivity of a High-Valent Nickel(IV) Oxido Complex

A reactive
high-valent dinuclear nickel­(IV) oxido bridged complex
is reported that can be formed at room temperature by reaction of
[(L)2Ni­(II)2(μ-X)3]­X (X = Cl
or Br) with NaOCl in methanol or acetonitrile (where L = 1,4,7-trimethyl-1,4,7-triazacyclononane).
The unusual Ni­(IV) oxido species is stabilized within a dinuclear
tris-μ-oxido-bridged structure as [(L)2Ni­(IV)2(μ-O)3]2+. Its structure and its
reactivity with organic substrates are demonstrated through a combination
of UV–vis absorption, resonance Raman, 1H NMR, EPR,
and X-ray absorption (near-edge) spectroscopy, ESI mass spectrometry,
and DFT methods. The identification of a Ni­(IV)-O species opens opportunities
to control the reactivity of NaOCl for selective oxidations.

本研究报道了一种具有反应活性的高价双核四价镍桥氧配合物。该配合物可在室温下由[(L)₂Ni(II)₂(μ-X)₃]X（X=Cl或Br）与次氯酸钠在甲醇或乙腈中反应制得，其中配体L为1,4,7-三甲基-1,4,7-三氮杂环壬烷。该罕见的四价镍氧物种以双核三μ-桥氧结构[(L)₂Ni(IV)₂(μ-O)₃]²⁺的形式得以稳定。通过紫外-可见吸收光谱、共振拉曼光谱、核磁共振氢谱、电子顺磁共振波谱、X射线吸收（近边）光谱、电喷雾电离质谱以及密度泛函理论（Density Functional Theory）计算等多种表征手段，本研究对该配合物的结构及其与有机底物的反应活性进行了系统表征。对四价镍-氧物种的成功鉴定，为调控次氯酸钠的反应活性以实现选择性氧化开辟了新的研究机遇。