Redox Induced Electron Transfer in Doublet Azo-Anion Diradical Rhenium(II) Complexes. Characterization of Complete Electron Transfer Series

Reactions of dirhenium decacarbonyl with the two azoaromatic ligands, La = (2-phenylazo)pyridine and Lb = (4-chloro-2-phenylazo)pyridine (general abbreviation of the ligands is L) afford paramagnetic rhenium(II) complexes, [ReII(L•−)2(CO)2] (1) (S = 1/2 ground state) with two one-electron reduced azo-anion radical ligands in an octahedral geometrical arrangement. At room temperature (300 K) the complexes 1a−b, showed magnetic moments (μeff) close to 1.94 μB, which is suggestive of the existence of strong antiferromagnetic interactions in the complexes. The results of magnetic measurements on one of the complexes, 1b, in the temperature range 2−300 K are reported. The above complexes showed two cathodic and two anodic responses in cyclic voltammetry where one-electron oxidation leads to an unusual redox event involving simultaneous reduction of the rhenium(II) and oxidation of the second ligand via intramolecular electron transfer. The oxidized complexes 1a+ and 1b+ are air stable and were isolated as crystalline solids as their tri-iodide (I3−) salts. The structures of the two representative complexes, 1b and [1b]I3, as determined by X-ray crystallography, are compared. The anionic complexes, [1]− and [1]2− were characterized in solution by their spectral properties.

十羰基二铼与两种芳香偶氮配体（La为(2-苯基偶氮)吡啶，Lb为(4-氯-2-苯基偶氮)吡啶，配体通用缩写为L）发生反应，生成顺磁性二价铼配合物[ReⅡ(L·⁻)₂(CO)₂]（配合物1），该配合物基态自旋S=1/2，中心金属与两个单电子还原的偶氮阴离子自由基配体形成八面体几何构型。室温（300 K）下，配合物1a~1b的有效磁矩（μeff）约为1.94 μB，表明该类配合物中存在强反铁磁相互作用。本文报道了配合物1b在2~300 K温度区间内的磁学测试结果。上述配合物在循环伏安测试中呈现两对氧化还原峰（两个阴极响应与两个阳极响应）；单电子氧化过程会引发一类特殊的氧化还原事件：通过分子内电子转移，同时实现二价铼的还原与第二配体的氧化。氧化态配合物1a⁺与1b⁺具有空气稳定性，可分离得到其三碘化物（I₃⁻）盐的单晶固体。本文对通过X射线单晶衍射解析得到的代表性配合物1b及其盐[1b]I₃的晶体结构进行了对比分析。阴离子配合物[1]⁻与[1]²⁻在溶液中通过光谱性质完成了结构表征。