OPTICALLY-ACTIVE RUTHENOCENYLBIS(PHOSPHINES) - NEW EFFICIENT CHIRAL PHOSPHINE-LIGANDS FOR CATALYTIC ASYMMETRIC REACTIONS

New optically active ruthenocenylbis(phosphines) (R)-N,N-dimethyl-1-[(S)-1'2-bis(diphenylphosphino)-ruthenocenyl]propylamine [(R)-(S)-Et-BPPRA] (5a) and its ethylamine analog [(R)-(S)-BPPRA] (5b) were prepared by way of stereoselective lithiation of (R)-N,N-dimethyl-1-ruthenocenylalkylamines (4), which were obtained by the asymmetric ethylation or methylation (>96% ee) of ruthenocenecarboxaldehyde with the corresponding dialkylzincs in the presence of a catalytic amount of an optically active aminoalcohol 2 followed by stereoretentive amination of the resulting (R)-1-ruthenocenylalkanols (3). An X-ray diffraction study of the crystal structure of PdCl2[(R)-(S)-Et-BPPRA] (6a) revealed that the P-Pd-P bite angle of the ruthenocenylbis(phosphine) complex (100.47 degrees) is larger than that of the ferrocene analog and the phenyl rings on the phosphorus atoms are located closer to the chlorine ligand and palladium atom, suggesting that the ruthenocenylphosphines are more enantioselective chiral ligands for asymmetric reactions catalyzed by transition metal complexes. Actually, the ruthenocenylphosphines gave high enantioselectivity (higher than the ferrocene analog) in the palladium-catalyzed asymmetric silylation of allylic chlorides with 1,1-dichloro-1-phenyl-2,2,2-trimethyldisilane (PhCl(2)SiSiMe(3)) (up to 92% ee) and in the palladium-catalyzed cyclization of 2-butenylene dicarbonate with methyl acetylacetate forming a vinyldihydrofuran (up to 86% ee).