Two new manganese(III) complexes, [pyH][Mn(Br₄Cat)₂(py)] (1) and [Mn(Br₄Cat)(Br₃pyCat)(py)₂] (2), where py is pyridine, Br₄CatH₂ is tetrabromocatechol and Br₃pyCatH₂ is 3,5,6-tribromo-4-pyridiniumcatechol, derived from redox ‘noninnocent’ bromo-substituted catecholate ligands are reported. Both complexes were characterized by various spectroscopic techniques in addition to the single crystal X-ray crystallography, and the electrochemical behavior of these complexes was investigated by cyclic voltammetry. Variable temperature UV–vis spectral studies for complex 1 reveal an unprecedented observation in which a dramatic increase of the ligand-to-metal charge transfer band at 592 nm associated with concomitant change in color of the solution from olive-green to dark-green is noticed with increase in temperature. This unprecedented spectral feature is consistent with the formation of a new species 2 in which valence tautomerism induced aromatic nucleophilic substitution of a tetrabromocatecholate ligand by pyridine is observed. DFT calculations have been used to rationalize this unexpected result. To the best of our knowledge, the nucleophilic aromatic substitution of tetrabromosemiquinone by pyridine to generate this pyridinium-containing catecholate ligand is the first example of valence tautomerism induced nucleophilic ipso substitution by a nitrogen containing ligand. Although the electrochemical behavior of both complexes is similar, the probable role of a positive charge on the ligand backbone has been discussed in order to justify the significantly higher catalytic activity of complex 2 over complex 1.

中文翻译：

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价互变异构诱导的四溴儿茶酚酸酯配体中的亲核ipso取代和模仿苯恶嗪酮合酶功能的多种催化活性

两种新的锰（III）配合物[pyH] [Mn（Br ₄ Cat）₂（py）]（1）和[Mn（Br ₄ Cat）（Br ₃ pyCat）（py）₂ ]（2），其中py是吡啶，Br ₄ CatH ₂是四溴邻苯二酚，Br ₃ pyCatH ₂据报道有3，5，6-三溴-4-吡啶基儿茶酚，其衍生自氧化还原“非纯”溴取代的儿茶酚酸酯配体。除单晶X射线晶体学外，还通过各种光谱技术对这两种配合物进行了表征，并通过循环伏安法研究了这些配合物的电化学行为。复杂化合物1的可变温度紫外-可见光谱研究显示了前所未有的观察结果，其中592 nm处配体-金属电荷转移带的急剧增加与溶液颜色从橄榄绿到深绿色的伴随变化相关。随着温度的升高而注意到。这种前所未有的光谱特征与新物种的形成一致2其中观察到价互变异构体诱导吡啶诱导的四溴邻苯二酚配体的芳香亲核取代。DFT计算已用于合理化此意外结果。据我们所知，吡啶对四溴半醌的亲核芳族取代以生成该含吡啶鎓的儿茶酚酸酯配体是价互变异构诱导的氮原子配体诱导亲核ipso取代的第一个例子。尽管两种配合物的电化学行为都相似，但是为了证明配合物2相对于配合物1具有更高的催化活性，已对正电荷在配体主链上的可能作用进行了讨论。