NO Disproportionation Reactivity of Fe Tropocoronand Complexes

The synthesis and characterization of divalent [Fe(TC-5,5)] (1) and trivalent [Fe(OTf)(TC-5,5)] (2)
tropocoronand complexes are described. Compound 1 reacts with 1 equiv of NO to form the {FeNO}7 complex
3. A single-crystal X-ray structure determination of 3 reveals a trigonal bipyramidal geometry with a linearly
coordinated nitrosyl (Fe−N−O = 174.3(4)°) having a short Fe−N distance of 1.670(4) Å. EPR and Mössbauer
spectroscopy, SQUID susceptometry, and normal coordinate analysis indicate 3 to be a low-spin {FeIII(NO-)}2+
species. In the presence of excess NO, 3 converts to a metastable nitrosyl−nitrito complex that decomposes
by losing NO2, which subsequently nitrates the aromatic tropolone rings of the ligand. The final products of
the NO disproportionation reaction are N2O and [Fe(NO)(TC-5,5-NO2)] (4). The νNO stretching band of 4 is
increased to 1716 cm-1 from its value of 1692 cm-1 in 3, owing to the electron-withdrawing nitro groups on
the ligand, and the compound no longer promotes the disproportionation of NO. Mechanistic aspects of the
reaction are discussed.

本文报道了二价[Fe(TC-5,5)]（1）与三价[Fe(OTf)(TC-5,5)]（2）两类托酚冠烷（tropocoronand）配合物的合成与表征工作。化合物1与1当量的一氧化氮（NO）反应，生成{FeNO}7型配合物3。对配合物3的单晶X射线衍射结构解析结果显示，其呈现三角双锥几何构型，配位亚硝酰基呈直线型排布（Fe−N−O键角为174.3(4)°），Fe−N键长仅为1.670(4)埃（Å）。结合电子顺磁共振（EPR）波谱、穆斯堡尔（Mössbauer）谱学、超导量子干涉器件（SQUID）磁强测量以及简正坐标分析的结果，可确定配合物3为低自旋的{FeIII(NO-)}2+物种。在过量一氧化氮存在的条件下，配合物3会转化为一种亚稳态的亚硝酰-亚硝酸根配合物；该配合物通过释放二氧化氮（NO₂）发生分解，进而对配体的芳构托酚酮环进行硝化修饰。一氧化氮歧化反应的最终产物为一氧化二氮（N₂O）与[Fe(NO)(TC-5,5-NO₂)]（4）。由于配体上引入了吸电子硝基，配合物4的NO伸缩振动峰波数从3中的1692 cm⁻¹提升至1716 cm⁻¹，且该化合物不再能够催化一氧化氮的歧化反应。本文最后对该反应的机理进行了探讨。