The preparation and study of bis(2-quinolyl) and bis(2-[1,8]naphthyridyl) derivatives of pyrimidine and pyrazine as bridging ligands for RuII

The 2:1 Friedlander condensation of 2-aminobenzaldehyde or 2-aminonicotinaldehyde with either 4,6-diacetylpyrimidme or 2,5-diacetylpyrazine leads to a family of four new bis(bidentate) bridging ligands. Subsequent complexation of these ligands with [RuCl2(bpy)(2)] (bpy = 2,2'-bipyridine) leads to the corresponding mononuclear and dinuclear mixed-ligand Ru-II complexes. Analysis of the H-1 NMR spectra of these systems affords some insight into their conformational properties. Electronic spectra of the complexes evidence two long-wavelength absorption bands which correspond to typical metal-to-ligand charge transfer states. The energies of these states may be explained by electronegativities of the pendant rings on the bridging ligand as well as the substitution pattern on the central ring. For the dinuclear complexes the lowest energy absorption shows components associated with coordination to the pendant and the central rings. The appearance of two metal-based oxidations gives good evidence for strong intermetalic interaction and Koopman's theorem is obeyed for all systems. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.