Chiral pyridylimidazolines: synthesis, arene ruthenium complexes and application in asymmetric catalysis

Condensation of (1S,2S)-1,2-diphenylethylenediamine and 2-cyanopyridine gives the chiral pyridylimidazoline (L1), deprotonation followed by treatment with methyl iodide gives an NMe derivative (L2). The pyridylimidazolines react with [RuCl2(mes)]2 (mes = 1,3,5-trimethylbenzene) in the presence of NaSbF6 to give [RuCl(L)(mes)][SbF6] (1,2) which have been characterised by X-ray crystallography. After treatment with AgSbF6 both complexes are enantioselective catalysts for the Diels–Alder reaction of methacrolein and cyclopentadiene.