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

New optically active ruthenocenylbis(phosphines) '2-bis(diphenylphosph ino)-ruthenocenyl]propylamine [(R)-(S)-Et-BPPRA] (5a) and its ethylami ne analog [(R)-(S)-BPPRA] (5b) were prepared by way of stereoselective lithiation of (R)-N,N-dimethyl-1-ruthenocenylalkylamines (4), which w ere obtained by the asymmetric ethylation or methylation (>96% ee) of ruthenocenecarboxaldehyde with the corresponding dialkylzincs in the p resence of a catalytic amount of an optically active aminoalcohol 2 fo llowed by stereoretentive amination of the resulting (R)-1-ruthenoceny lalkanols (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 th e ruthenocenylbis(phosphine) complex (100.47 degrees) is larger than t hat of the ferrocene analog and the phenyl rings on the phosphorus ato ms are located closer to the chlorine ligand and palladium atom, sugge sting that the ruthenocenylphosphines are more enantioselective chiral ligands for asymmetric reactions catalyzed by transition metal comple xes. Actually, the ruthenocenylphosphines gave high enantioselectivity (higher than the ferrocene analog) in the palladium-catalyzed asymmet ric silylation of allylic chlorides with 1,1-dichloro-1-phenyl-2,2,2-t rimethyldisilane (PhCl(2)SiSiMe(3)) (up to 92% ee) and in the palladiu m-catalyzed cyclization of 2-butenylene dicarbonate with methyl acetyl acetate forming a vinyldihydrofuran (up to 86% ee).