Abstract
Carbonyl complexes with manganese(I) as the central metal are very attractive catalysts. The introduction of redox-active ligands, such as quinones and methyl viologen analogs into these catalysts, would be expected to lead to superior catalyst performances, since they can function as excellent electron carriers. In this study, we synthesized four tricarbonylmanganese(I) complexes containing typical bidentate polypyridyl ligands, including 1,10-phenanthroline (phen) and 2,2′-bipyridine (bpy) frameworks bound to redox-active ortho-quinone/catechol or methyl viologen-like units. The molecular structures of the resulting complexes were determined by X-ray crystallography to clarify their steric features. As expected from the infrared (IR) data, three CO ligands for each complex were coordinated in the facial configuration around the central manganese(I) atom. Additionally, the structural parameters were found to differ significantly between the quinone/catechol units. Electrochemical analysis revealed some differences between them and their reference complexes, namely [MnBr(CO)3(phen)] and [MnBr(CO)3(bpy)]. Notably, interconversions induced by two-electron/two-proton transfers between the quinone and catechol units were observed in the phenanthroline-based complexes. This work indicated that the structural and redox properties in tricarbonylmanganese(I) complexes were significantly affected by chemically modified polypyridyl ligands. A better understanding of structures and redox behaviors of the present compounds would facilitate the design of new manganese complexes with enhanced properties.
Highlights
Due to the fact that manganese, a Group 7 element, is located in the center of the d-block elements on the periodic table, it has the widest oxidation number of the first-row transition metals (i.e., +7 state).As a result of its unique properties, manganese compounds such as KMnO4 and MnO2 have long been used as versatile oxidants and oxidation catalysts
Interconversions induced by two-electron/two-proton transfers between the quinone and catechol units were observed in the phenanthroline-based complexes
Manganese is present in the oxygen-evolving complex (OEC) that takes part in photosynthesis, where it plays an important role in catalyzing the oxidation of water [1]
Summary
As a result of its unique properties, manganese compounds such as KMnO4 and MnO2 have long been used as versatile oxidants and oxidation catalysts. Manganese is present in the oxygen-evolving complex (OEC) that takes part in photosynthesis, where it plays an important role in catalyzing the oxidation of water [1]. Manganese compounds containing π-acidic ligands, such as carbonyl (CO), generally exhibit lower valences. In this type of compound, since manganese(I) is overwhelmingly abundant compared to similar d6 complexes of other noble metals (e.g., Re(I) or Ru(II) [2]); the replacement of these noble metals by first-row transition metals is of particular importance. We attempt the synthesis of a further manganese(I) system that
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