Interconversion of diastereomeric complexes involved in Rh(I)-catalyzed asymmetric hydrogenation: A (31P,31P) EXSY NMR study

摘要: Rhodium(I) complexes containing chiral chelating diphosphines, e.g. R,R-dipamp [(R,R)-1,2-bis(o-methoxy-phenylphenylphosphino)ethane] or S,S-chiraphos [(2S,3S)-bis(diphenylphosphino)butane] and a prochiral olefin, methyl (Z)-α-acetamidocinnamate (mac), form diastereomeric which differ only in enantiotopic face of the olefin is bound to rhodium can be observed by 31P NMR. The interconversion two diastereomers has been with (31P,31P)-{1H} 2D EXSY techniques for various mixing times, Tm, three different solvents (CD2Cl2, CD3OD CD3COCD3). results clearly demonstrate that both inter- intramolecular ligand exchange processes are occurring, cannot proceed exclusively complete mac dissociation followed readdition opposite face. new consistent previous DANTE NMR experiments. differing CD2Cl2, CD3COCD3 solutions suggest possibility solvent involvement rate-limiting step exchange. method appears choice elucidating qualitative pathway this complex system.