The geometric and electronic structure of a one-electron-oxidized nickel(II) bis(salicylidene)diamine complex.
The geometric and electronic structure of a one-electron-oxidized nickel(II) bis(salicylidene)diamine complex.
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DOI：
10.1002/anie.200701194
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发表时间：
2007-07
影响因子：
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通讯作者：
Tim Storr;E. Wasinger;R. Pratt;T. Stack
中科院分区：
文献类型：
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作者：
Tim Storr;E. Wasinger;R. Pratt;T. Stack
金属酶活性中心中过渡金属离子与亲基配体的协同作用是当前的研究热点。[1]为了理解金属离子与有机自由基相互作用的复杂性，人们研究了许多具有一个或多个有机自由基配体的过渡金属配合物。[2-4]取决于氧化还原活性轨道的相对能量，具有亲自由基配体的金属络合物可以在限制性描述中作为金属配体自由基（Mn+（LC））或高价金属络合物（M（n+ 1）+（LC））存在。在有利的能量下，通过配体场或温度的变化可以发生价态互变异构。[2，5-9]特别是，最近对镍（II）双存在很大兴趣。亚水杨基二胺配合物（方案1），[6-10]作为单电子氧化形式1+、2+和3+，已经报道在NiII（LC 13）和NiIII（L23）形式之间表现出温度依赖性的价态互变异构现象。缺乏结构数据。在这里，我们报告的X-射线晶体结构的镍-配体-自由基配合物（1+），它有一个收缩的协调领域相对于其中性类似物1。1（ΔE= 500 mV）与Cu（Δ E = 205 mV）和Zn（ΔE= 175 mV）类似物循环伏安图中前两个氧化波之间的差异[11]表明，1+是系列中离域最大的。[12]有趣的是，1+是唯一不能将苯甲醇氧化成苯甲醛的衍生物。一个高度离域的结构，1+的进一步支持存在一个强烈的低能量吸收带在4700 cm-1，这表明，1+是最好的描述为第三类混合价化合物。[12]本文报道的改进的氧化方法允许氧化后的结构变化进行调查和价互变异构现象得到澄清。用1当量的氧化剂AgSbF 6（E1/2=+650 mV vs. Fc/Fc+; Fc：二茂铁）或噻蒽基自由基[噻蒽]+ CSbF 6 [13]（E1/2=+890 mV vs. Fc/Fc+）在CH 2Cl 2中处理络合物1，导致颜色立即从棕色变为绿色，这表明形成了1+离子。氧化络合物在CH 2Cl 2中的溶液在不存在H2O的情况下在室温下稳定数周。其他人[8，9]报道的快速分解可能是由于（NH 4）2Ce（NO3）6氧化剂，因为1+的Cu类似物在硝酸盐存在下快速分解。[11]在本文报道的氧化条件下1+的稳定性提高，允许分离适合于X射线结构分析的1+-SbF 6的单晶（图1）。[14]苯氧基自由基络合物（CrIII，[15] CuII，[16]和ZnII [17]）的结构数据有限，这是NiII-苯氧基络合物的第一个结构表征。
The cooperativity of transition-metal ions and proradical ligands in metalloenzyme active sites is of current research interest.[1] In an effort to understand the intricacies of the interaction of metal ions with organic radicals, many transition-metal complexes with one or more organic radical ligands have been studied.[2–4] Depending on the relative energies of the redox-active orbitals, metal complexes with proradical ligands can exist in a limiting description as a metal–ligand-radical (Mn+(LC)) or a high-valent metal complex (M (n+ 1)+(LÀ)). Given favorable energetics, valence tautomerism can occur through variation of the ligand field or temperature.[2, 5–9] In particular, much recent interest exists in nickel (II) bis (salicylidene) diamine complexes (Scheme 1),[6–10] as the one-electron-oxidized forms 1+, 2+, and 3+ have been reported to exhibit temperature-dependent valence tautomerism between NiII (LCÀ) and NiIII (L2À) forms.Although extensive spectroscopic and electrochemical data exists for such oxidized complexes, structural data is lacking. Herein we report the X-ray crystal structure of a NiII–ligand-radical complex (1+), which has a contracted coordination sphere relative to its neutral analogue 1. The difference between the first two oxidation waves in the cyclic voltammogram of 1 (ΔE= 500 mV) and those of the Cu (ΔE= 205 mV) and Zn (ΔE= 175 mV) analogues [11] indicates that 1+ is the most delocalized of the series.[12] Interestingly, 1+ is the only derivative that is unable to oxidize benzyl alcohol to benzaldehyde. A highly delocalized structure for 1+ is further supported by the presence of an intense low-energy absorption band at 4700cmÀ1, which suggests that 1+ is best described as a classIII mixed-valence compound.[12] The improved oxidation method reported herein allows the structural changes upon oxidation to be investigated and the valence tautomerism to be clarified. Treatment of complex 1 with 1 equivalent of the oxidants AgSbF6 (E1/2=+ 650 mV vs. Fc/Fc+; Fc: ferrocene) or the thianthrenyl radical [thianthrene]+ CSbF6 À [13](E1/2=+ 890 mV vs. Fc/Fc+) in CH2Cl2 results in an immediate color change from brown to green, which signifies formation of the 1+ ion. Solutions of the oxidized complex in CH2Cl2 are stable for weeks at room temperature in the absence of H2O. The quick decomposition reported by others [8, 9] may be due to the (NH4) 2Ce (NO3) 6 oxidant, as the Cu analogue of 1+ decomposes rapidly in the presence of nitrate.[11] The improved stability of 1+ under the oxidation conditions reported herein allows the isolation of single crystals of 1+-SbF6 À suitable for X-ray structural analysis (Figure 1).[14] Limited structural data exists for phenoxyl radical complexes (CrIII,[15] CuII,[16] and ZnII [17]), and this is the first structural characterization of a NiII–phenoxyl complex.