Iridium complexes containing the first sugar dithioether ligands.: Application as catalyst precursors in asymmetric hydrogenation

The first family of sugar derivative dithioethers 1,2-O-isopropylidene-3,5-bis(methylsulfanyl)-, (+)-RiSSMe(2), 1,2-O-isopropylidene-3,5-bis(isopropylsulfanyl)-, (+)-RiSSPr(2)(i), and 1,2-O-isopropylidene-3,5-bis(phenylsulfanyl)-alpha-D-(+)-ribofuranose, (+)-RiSSPh(2), was prepared from 1,2-O-isopropylidene-3,5-di-O-trifluoromethanesulfonyl-D-xylofuranose. Reaction of these chiral C-1 symmetrical dithioether ligands with [Ir(cod)(2)]BF4 (cod = 1,5-cyclooctadiene) yielded the iridium complexes [Ir(cod){(+)-RiSSR(2)}]BF4 1-3. Their reaction with H-2 at 0 degrees C gave the cis-dihydridoiridium(III) complexes [IrH2(cod){(+)-RiSSR(2)}]BF4 4-6. Complexes 1-3 were tested in the asymmetric hydrogenation of acrylic acid derivatives at 1 bar of H-2 and room temperature, providing enantioselectivities of up to 62%.