'Chiral-at-metal' octahedral ruthenium(II) complexes with achiral ligands: A new type of enantioselective catalyst

摘要

cis-[Ru(dMP)(2)(CH3CN)(2)][PF6](2) (dmp = 2,9-dimethyl-1,10-phenanthroline), complex 1[PF6](2), exists in two enantiomeric forms, A and A. During treatment with the chiral anion tris[tetrachlorobenzene-1,2-bis(olato)] phosphate (V), also named Trisphat, in dichloromethane it has been possible to selectively precipitate each enantiomer, associated with Trisphat in the form of the heterochiral pair. This enantiomerically pure compound has been characterized in solution by UV-visible, CD, ESI-MS, and NMR spectroscopy and by X-ray crystallography in the solid state. Trisphat was also used as an NMR chiral shift reagent to determine the enantiomeric excess of the complex preparations. The "chiral-at-metal" ruthenium complex has been evaluated as a catalyst for the oxidation of sulfides to sulfoxides by hydrogen peroxide. The reactions displayed a low but significant level of enantioselectivity (18% ee in the case of 4-bromophenyl methyl sulfide). Our results thus provide the first demonstration that the chiral information carried by a stereogenic metal center can be catalytically transferred to molecules during stereoselective oxidation. [References: 24]