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

Abstract

The dinuclear ligand-bridged complex systems [{Ru(bpy)2}(μ-bpm)(Ru(Me2bpy)2}]4+ and [{Ru(bpy)(Me2bpy)}2-(μ-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}(μ-bpm)( Ru(Me2bpy)2)]4+ (viz. AA, ΔΔ, AA and AA) and the six stereoisomeric forms of [{Ru(bpy)(Me2bpyl}2-(μ-bpm)]4+ (viz. ΔΔ-trans, ΔΔ-cis, ΔΔ-trans, ΔΔ-cis, AA-trans, and AA-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}(μ-bpm){Ru(pp')2}]4+ (pp and pp' = bidentate polypyridyl ligands; pp ≠ pp').