Synthesis and structural chemistry of arene-ruthenium half-sandwich complexes bearing an oxazolinyl–carbene ligand

Reaction of a series of directly connected oxazoline–imidazolium salts with silver(I) oxide and subsequent transmetallation with [Ru(p-cymene)Cl2]2 and anion exchange with KPF6 cleanly gave the corresponding 2-oxazolinyl-(N-mesityl)imidazolidene(chloro)ruthenium(II) half-sandwich complexes [RuCl(oxcarb)(p-cymene)]PF6, two derivatives of which were characterized by X-ray diffraction. Abstraction of the chloro ligand furnished the dicationic aqua complexes [Ru(H2O)(oxcarb)(p-cymene)](PF6)2 which possess a similar coordination geometry. The syntheses were found to be highly diastereoselective, since only one diastereoisomer could be observed in all ruthenium complexes upon reaction of the chiral enantiopure oxazoline–imidazolium salts. Their potential as transfer hydrogenation and Lewis acid catalysts has been probed.