Hydroxyphenyl- and octoxyphenyl-substituted dipyrazinylpyridine complexes of ruthenium(II), iron(II) and nickel(II)

A water-soluble, hydroxyphenyl-substituted dipyrazinylpyridine (HOL) and its liposoluble, n-octylated derivative (C8OL) were prepared in short sequences and good yields. The monocarbonyldichlororuthenium(II) complex (C8OL)Ru(CO)Cl2 were obtained in cis and trans isomeric forms, which could be distinguished by their absorption, 13C NMR and 15N NMR spectra. The octahedral homoleptic complexes [(C8OL)2M]2+ (M = RuII, FeII) and five-coordinate (HOL)NiCl2 are also described. Density functional theory is used to derive optical geometries, optical spectra, a molecular orbital description and the electronic structure. The time-dependent calculations reveal that the strong visible-region absorption responsible for the color of the homoleptic FeII and RuII species arises mainly from an internal ligand charge-transfer process and only to a small degree from the expected metal-to-ligand CT process. The crystal structures of free C8OL, trans-(C8OL)Ru(CO)Cl2, [(C8OL)2Fe](FeCl4)2 and (HOL)NiCl2 were also obtained. Electrochemical data are also presented and discussed.