Asymmetric Reactions Catalyzed by Chiral Metal Complexes. LIV. Effects of the diarylphosphino groups of modified DIOPs on the enantioselectivity and the catalytic activity of their rhodium(I) complexes in the catalytic asymmetric hydrogenations of enamides.

Remarkable effects of the substituted diphenylphosphino groups of modified DIOPs on the enantioselectivity and the catalytic activity were observed in the asymmetric hydrogenation of an electron-rich olefin such as enamide using their rhodium(I) complexes as the catalyst. The cationic rhodium(I) complexes of modified DIOPs bearing electron-donating groups showed higher catalytic activities than that of original DIOP, and the cationic complexes showed better enantioselectivities than the corresponding neutral ones. The cationic rhodium(I) complex of p-methoxy-substituted DIOP was found to be the most efficient catalyst.