Asymmetric hydroformylation catalyzed by rhodium(I) complexes of novel chiral spiro ligands

Abstract

Chiral diphosphites and phosphinite-phosphites derived from spiro[4.4]nonane-1,6-diol were synthesized. Using Rh[I]-7 complex in asymmetric hydroformylation of styrene, high regioselectivity (97%) and moderate enantioselectivity (65% ee) have been obtained. This catalyst system was also effective for aryl-substituted olefins. The diphosphites 8 and 9 bearing 1,1′-binaphthyl backbones were tested and the opposite configuration of the product indicates that the sense of enantioface selection is mainly dictated by the configuration of the terminal groups. Phosphinite-phosphite ligands gave low enantiomeric excesses (up to 48% ee) and low b/n ratios. These results suggest that the regio- and enantioselectivity is mainly affected by the bulky substituents on terminal groups. The crystal structure of Rh(7)(acac) are presented. The distortion in the structure is indicative of a crowded rhodium center. © 1999 Elsevier Science S.A.