BINAP-Ru(II) and BINAP-Rh(I)-catalyzed asymmetric hydrogenation of olefins without heteroatom-functionalities

Asymmetric hydrogenation of 1,1′-disubstituted olefins which have no heteroatom functionalities to allow additional interactions with catalyst centers, have been investigated by use of Ru(II) and Rh(I) complexes of BINAP as catalysts. Enantioselectivities and the sense of asymmetric induction are highly dependent on the structure of substrates and the nature of catalysts. Hydrogenation of 1-methyleneidan (1a), a five-membered methylenecycloalkane, gave the highest optical yield (78%) when Ru(OAc)2((R)-binap) was used as catalyst, while the use of the catalyst system [RhI(cod)]2/(R)-BINAP afforded the highest ees (71–82%) for six-membered analogs, 1-methylenetetralin (4a) and its derivatives. In contrast, hydrogenation of seven-membered analog 7 and acyclic olefins 10 resulted in only moderate enantioselectivities by use of these catalysts. The BINAP-Ru(II) catalyzed hydrogenation exhibited a remarkable dependence of enantioselectivities on solvents, while a large anionic ligand effect was observed for the reaction with the BINAP-Rh(I) system. Based on these experimental results, mechanistic aspects of these asymmetric hydrogenation have been discussed.