Diastereomeric diphosphites (1-4) were prepared by the reaction of enantiomerically pure 2,2′-dihydroxy-5,5′,6,6′,7,7′,8,8′-octahydro-1, 1′-binaphthyl or 2,2′-dihydroxy-1,1′-binaphthyl with chlorophosphites. The structure of R-bis(4R,6R)-1 has been determined by X-ray diffraction. The new (1-2) and the known diphosphites (3-4) were tested in the platinum- and rhodium-catalyzed asymmetric hydroformylation of styrene. Systematic variation in chirality at both the chelate backbone and the terminal groups revealed a remarkable effect on the enantioselectivity of the catalysts. Ligand 3 generates chiral cooperativity of the backbone and the terminal moieties in platinum-catalyzed hydroformylation. The highest ee (65%) for 2-phenylpropanal was found for the ligand R-bis(S)-4 in combination with platinum. The chemoselectivities with all ligands described in association with platinum were rather low. The comparative study clearly showed that the platinum complexes of these diphosphites (1-4) gave higher enantioselectivities than the corresponding rhodium complexes in the asymmetric hydroformylation of styrene.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry