Synthesis and Coordination Chemistry of Novel Chiral P,S-Ligands with a Xylofuranose Backbone:  Use in Asymmetric Hydroformylation and Hydrogenation

A series of novel chiral thioether-phosphite ligands derived from 1,2- O -isopropylidenexylofuranose have been synthesized. Reaction of these chiral ligands with [M(cod) 2 ]BF 4 (M = Ir, Rh; cod = 1,5-cyclooctadiene) yielded the complexes [M(cod)(P−S)]BF 4 10 − 15 . The addition of H 2 to iridium complexes 12 − 15 gave the cis -dihydridoiridium(III) complexes [IrH 2 (cod)(P−S)]BF 4 19 − 21, which are present in only one diastereoisomeric form. Iridium complexes are active in the hydrogenation of itaconic acid and produce enantioselectivities of up to 51% under atmospheric pressure. They have also been tested in the Rh-catalyzed hydroformylation of styrene. We discuss hydroformylation results according to the solution structure of the species formed under hydroformylation conditions.