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Interconversion of diastereomeric complexes involved in Rh(I)‐catalyzed asymmetric hydrogenation: A ( 31 P, 31 P) EXSY NMR study
Author(s) -
Bircher Hansruedi,
Bender Bruce R.,
von Philipsborn Wolfgang
Publication year - 1993
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260310316
Subject(s) - chemistry , diastereomer , diphosphines , rhodium , stereochemistry , ligand (biochemistry) , olefin fiber , intramolecular force , chirality (physics) , dissociation (chemistry) , catalysis , medicinal chemistry , organic chemistry , biochemistry , nambu–jona lasinio model , receptor , chiral symmetry breaking , physics , quantum mechanics , quark
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 [(2 S ,3 S )‐bis(diphenylphosphino)butane] and a prochiral olefin, e.g. methyl ( Z )‐α‐acetamidocinnamate (mac), form diastereomeric complexes which differ only in which enantiotopic face of the olefin is bound to rhodium and can be observed by 31 P NMR. The interconversion of the two diastereomers has been observed with ( 31 P, 31 P)‐{ 1 H} 2D EXSY techniques for various mixing times, T m , and in three different solvents (CD 2 Cl 2 , CD 3 OD and CD 3 COCD 3 ). The results clearly demonstrate that both inter‐ and intramolecular ligand exchange processes are occurring, and that diastereomeric interconversion cannot proceed exclusively by complete mac dissociation followed by readdition to the opposite enantiotopic olefin face. The new results are consistent with previous DANTE NMR experiments. The differing results in CD 2 Cl 2 , CD 3 OD and CD 3 COCD 3 solutions suggest the possibility of solvent involvement in the rate‐limiting step of ligand exchange. The 2D EXSY method appears to be the method of choice for elucidating the qualitative exchange pathway of this complex system.