Evidence for the importance of conformational equilibria in Rh-diphosphine complexes for the enantioselection in Rh-catalyzed asymmetric hydrogenation

The conformations of the chelate cycles in the X-ray structures of norbornadiene- and cyclooctadiene-rhodium complexes of (R,R)-1,2-bis[(o-methylphenyl)phenylphosphino]ethane are dramatically different. Nevertheless, they demonstrate the same sense of enantioselection in asymmetric hydrogenation of dehydroamino acids.