Synthesis of chiral diphosphite ligands and comparison of their rhodium and platinum complexes in the asymmetric hydroformylation of styrene

Diastereomeric diphosphites (1-4) were prepared by the reaction of enantiom erically 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,GR)-1 has been determined by X-ray diffraction. The new (1-2) and t he known diphosphites (3-4)were tested in the platinum- and rhodium-catalyz ed asymmetric hydroformylation of styrene, Systematic variation in chiralit y at both the chelate backbone and the terminal groups revealed a remarkabl e effect on the enantioselectivity of the catalysts. Ligand 3 generates chi ral cooperativity of the backbone and the terminal moieties in platinum-cat alyzed hydroformylation. The highest ee (65%) for 2-phenylpropanal was foun d for the ligand R-bis(S)-4 in combination with platinum. The chemoselectiv ities with all ligands described in association with platinum were rather l ow. The comparative study clearly showed that the platinum complexes of the se diphosphites (1-4) gave higher enantioselectivities than the correspondi ng rhodium, complexes in the asymmetric hydroformylation of styrene. (C) 19 99 Elsevier Science S.A. All rights reserved.