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. ΔΛ, ΛΔ, ΔΔ and ΛΛ) and the six stereoisomeric forms of [{Ru(bpy)(Me₂bpy)}₂(μ-bpm)]⁴⁺ (viz. ΔΛ-trans, ΔΛ-cis, ΔΔ-trans, ΔΔ-cis, ΛΛ-trans, and ΛΛ-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′).