Hydroquinone/quinone electro- and photochemical interconversion in isolable polypyridylruthenium(II) complexes.

Quinone derivatives and their metal complexes are well-known molecules that participate in electron-transfer reactions relevant to diverse fields. However, the fundamental knowledge on the unique reactivity of redox-active quinone complexes is limited by the difficulty in their isolation. Herein, the synthesis of isolable mononuclear polypyridylruthenium(ii) complexes containing both hydroquinone and quinone units is described. Three types of monodentate ligands are conveniently used to control the electronic states of the complexes. Both reduced (hydroquinone) and oxidised (quinone) forms are successfully isolated and characterised by spectroscopic and crystallographic analysis, allowing direct comparisons of their properties. The redox-rich and visible light-responsive nature of the ruthenium complexes enables to investigate the quinone/hydroquinone interconversion induced by electron transfer, photoirradiation and photoswitching based on ligand substitution reactions. These results demonstrate the occurrence of synergistic effects between metal complexes and redox-active organic compounds.

Effects of Chemically-Modified Polypyridyl Ligands on the Structural and Redox Properties of Tricarbonylmanganese(I) Complexes.

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.

Synthesis and crystal structures of manganese(I) carbonyl complexes bearing ester-substituted α-di-imine ligands.

The crystal structures of two manganese(I) complexes with ester-substituted bi-pyridine or bi-quinoline supporting ligands are reported, namely, fac-bromido-tricarbon-yl(diethyl 2,2'-bi-pyridine-4,4'-di-carboxyl-ate-κ2 N,N')mangan-ese(I), [MnBr(C16H16N2O4)(CO)3], I, and fac-bromido-tricarbon-yl(diethyl 2,2'-bi-quinoline-4,4'-di-carboxyl-ate-κ2 N,N')manganese(I), [MnBr(C24H20N2O4)(CO)3], II. In both complexes, the manganese(I) atom adopts a distorted octa-hedral coordination sphere defined by three carbonyl C atoms, a Br- anion and two N atoms from the chelating α-di-imine ligand. Both complexes show fac configurations of the carbonyl ligands. In I, the complex mol-ecules are linked by C-H⋯Br hydrogen bonds and aromatic π-π contacts. In II, intra-molecular C-H⋯O hydrogen bonds are present as well as inter-molecular C-H⋯O and C-H⋯Br hydrogen bonds and π-π inter-actions.