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

The dinuclear ligand-bridged complex systems [{Ru(bpy)(2)}(mu-bpm){Ru(Me(2)bpy)(2)}](4+) and [{Ru(bpy)(Me(2)bpy)}(2)(mu-bpm)](4+) (bpm = 2,2'-bipyrimidine; bpy = 2,2'-bipyridine; Me(2)bpy = 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)}(mu-bpm){Ru(Me(2)bpy)(2)}](4+) (viz. DeltaLambda, LambdaDelta, DeltaDelta and Lambda) and the six stereoisomeric forms of [{Ru(bpy)(Me(2)bpy)}(2)(mu-bpm)](4+) (viz. DeltaLambda-trans, DeltaLambda-cis, DeltaDelta-trans, DeltaDelta-cis, LambdaLambda-trans, and LambdaLambda-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 not equal pp').