Synthetic and stereochemical studies of dinuclear ruthenium(II) complexes with mixed terminal ligands

The dinuclear ligand-bridged complex systems [{Ru(bpy)2}(µ-bpm){Ru(Me2bpy)2}]4+ and [{Ru(bpy)(Me2bpy)} 2(mu-bpm)]4+ (bpm = 2,2-bipyrimidine; bpy = 2,2-bipyridine; Me2bpy = 4,4-dimethyl-2,2-bipyridine) exhibit a range of stereoisomers – diastereoisomers, enantiomers and geometric isomers. From synthetic procedures producing mixtures of all possible forms of the respective complexes, the four stereoisomeric forms of the [{Ru(bpy)2}(mubpm){Ru(Me2bpy)2}]4+ (viz., , and ) and the six stereoisomeric forms of [{Ru(bpy)(Me2bpy)}2(mu-bpm)]4+ (viz.trans, -cis, -trans, -cis, -trans, and -cis) have been isolated using cation-exchange chromatographic techniques. This is the first reported separation of the stereoisomers for a system of the type [{Ru(pp)2}(mu-bpm){Ru(pp)2}]4 + (pp and pp = bidentate polypyridyl ligands; pp pp).