Arene ruthenium complexes with pyridyloxazolines: synthesis and applications as asymmetric catalysts for Diels–Alder reactions †

Abstract

Reaction of the dimers [RuCl₂(arene)]₂ with pyridyloxazolines (pymox) gave complexes [RuCl(pymox)(arene)][SbF₆] 1–12 which have been fully characterised. Using chiral ligands diastereomers are formed, the diastereoselectivity depending on the substituents on the arene and on the oxazoline. The complexes [RuCl(Me₂-pymox)(mes)][SbF₆] 1, [RuCl(Ph-pymox)(mes)][SbF₆] 3, [RuCl(ⁱPr-pymox)(mes)][SbF₆] 5 and [RuCl(indanyl-pymox)(mes)][SbF₆] 12 (mes = mesitylene) have been characterised by X-ray crystallography. Treatment of these cations with AgSbF₆ generates dications which in some cases can be isolated as aqua species [Ru(OH₂)(pymox)(arene)]²⁺; these dications are enantioselective catalysts for Diels–Alder reactions of acroleins and dienes; a mechanism is proposed which accounts for the observed enantioselectivity.