Department of Chemistry, 1102 Natural Sciences II, University of California, Irvine, California 92697, USA.
Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA.
Dalton Trans. 2021 Jun 15;50(23):8111-8119. doi: 10.1039/d1dt01021b.
Bimetallic active sites are ubiquitous in metalloenzymes and have sparked investigations of synthetic models to aid in the establishment of structure-function relationship. We previously reported a series of discrete bimetallic complexes with [FeIII-(μ-OH)-MII] cores in which the ligand framework provides distinct binding sites for two metal centers. The formation of these complexes relied on a stepwise synthetic approach in which an FeIII-OH complex containing a sulfonamido tripodal ligand served as a synthon that promoted assembly. We have utilized this approach in the present study to produce a new series of bimetallic complexes with [FeIII-(μ-OH)-MII] cores (M = Ni, Cu, Zn) by using an ancillary ligand to the FeIII center that contains phosphinic amido groups. Assembly began with formation of an FeIII-OH that was subsequently used to bind the MII fragment that contained a triazacyclononane ligand. The series of bimetallic complexes were charactered structurally by X-ray diffraction methods, spectroscopically by absorption, vibrational, electron paramagnetic resonance spectroscopies, and electrochemically by cyclic voltammetry. A notable finding is that these new [FeIII-(μ-OH)-MII] complexes displayed significantly lower reduction potentials than their sulfonamido counterparts, which paves way for future studies on high valent bimetallic complexes in this scaffold.
双金属活性位点在金属酶中普遍存在，并激发了对合成模型的研究，以帮助建立结构-功能关系。我们之前报道了一系列具有[FeIII-(μ-OH)-MII]核的离散双金属配合物，其中配体框架为两个金属中心提供了独特的结合位点。这些配合物的形成依赖于逐步合成方法，其中含有磺酰胺三齿配体的 FeIII-OH 配合物作为缩合剂促进组装。在本研究中，我们使用含有膦酰基酰胺基团的辅助配体到 FeIII 中心，利用这种方法产生了一系列具有[FeIII-(μ-OH)-MII]核（M = Ni、Cu、Zn）的新的双金属配合物。组装始于形成 FeIII-OH，随后用于结合含有三氮杂环壬烷配体的 MII 片段。通过 X 射线衍射、吸收光谱、振动光谱、电子顺磁共振光谱和循环伏安法对一系列双金属配合物进行了结构表征。一个显著的发现是，这些新的[FeIII-(μ-OH)-MII]配合物的还原电位明显低于它们的磺酰胺对应物，这为在该支架中研究高价双金属配合物铺平了道路。
