Stereochemistry in tris(bidentate ligand)ruthenium(II) complexes containing unsymmetrical polypyridyl ligands

Abstract

The synthesis and stereochemistry of monomeric ruthenium(II) complexes containing the unsymmetrical bidentate ligand pmbipy [4-(2,2-dimethylpropyl)-4′-methyl-2,2′-bipyridine] have been studied. In the complexes [Ru(dmbipy)(pmbipy)(CO)₂]²⁺(dmbipy is the symmetrical bidentate ligand 4,4′-dimethyl-2,2′-bipyridine) and [Ru(pmbipy)₂(CO)₂]²⁺, the geometric isomers (two and three, respectively) have been identified and characterized by NMR techniques, and one isomer of each species has been isolated in a pure form by fractional recrystallization. The dicarbonyl species have both been used as precursors for the synthesis of [Ru(dmbipy)(pmbipy)₂]²⁺ by a decarbonylation process: under certain conditions, the conversion was shown to take place with retention of the stereochemical relationship of the two ligands in the dicarbonyl precursor. Mixtures of the three geometric isomers of [Ru(dmbipy)(pmbipy)₂]²⁺ were separated by cation-exchange chromatography, and the isomers characterized by NMR techniques. The complex [Ru(pmbipy)₃²⁺ was synthesized, and the two geometric isomers separated and characterized in a similar manner.