Asymmetric hydroformylation of styrene using rhodium and platinum complexes of diphosphites containing chiral chelate backbones and chiral 1,3,2-dioxaphosphorinane moieties

Several chiral diphosphite ligands containing six stereogenic centres were synthesised and tested in order to study chiral cooperativity in the Rh- and Pt-catalysed asymmetric hydroformylation of styrene. The ligands were prepared either by the reaction of 2,4-pentanediol enantiomers with (4R,6R)-4,6-dimethyl-2-chloro-1,3,2-dioxaphosphorinane or that of (1S,3S)-1,3-diphenyl-1,3-propanediol with 4,6-dimethyl-2-chloro-1,3,2-dioxaphosphorinane enantiomers. Thus the chirality was varied both in the chelate backbone and in the terminal groups of the ligands. In case of Pt-catalysed hydroformylation, the stereogenic elements in the bridge have been found to be determinate for the product configuration with a cooperative effect from the terminal groups when the constellations are matched with 40% e.e. maximum enantioselectivity. Some coordination chemistry and the crystal structure determination of these ligands are also reported.