Formation of optically active [Ru(bipy)2Cl2](bipy = 2,2′-bipyridyl) by photodissociation of [Ru(bipy)3]Cl2 in dichloromethane

Abstract

An optically active bis-chelated complex, [Ru(bipy)₂Cl₂](bipy = 2,2′-bipyridyl), has been obtained when enantiomeric [Ru(bipy)₃]Cl₂ was illuminated by visible light in dichloromethane. From the dependence of the optical purity of the product on light intensity, it is proposed that the reaction from Δ-[Ru(bipy)₃]Cl₂ to Δ-[Ru(bipy)₂Cl₂](chirality retention) proceeds by way of the dissociation of a monodentate ligand, bipy*, from a photoactivated intermediate, Δ-[Ru(bipy)₂(bipy*)Cl]Cl in the dark, while the reaction to Λ-[Ru(bipy)₂Cl₂](chirality inversion) involves the further photoactivated configurational change of Δ-[Ru(bipy)₂(bipy*)Cl]Cl to Λ-[Ru(bipy)₂(bipy*)Cl]Cl. Racemization is avoided under the conditions of weak light and high temperature. The synthetic value of optically active [Ru(bipy)₂Cl₂] as a chiral intermediate has been exemplified by preparing a new chiral amphiphilic ruthenium(II) complex.