Double Stereoselection in Hydrogenation of Prochiral Dehydrocarboxylic Acids on Rh(S,S-DIODMA)2+TfO – Complex in the Presence of (+)-Neomenthyldiphenylphosphine
L. О. Nindakova, О. V. Gamzikova, B. А. Shainyan and F. К. Schmidt
Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences,
Ul. Favorskogo 1, Irkutsk 664033 (Russia),
E-mail: bagrat@irioch.irk.ru
Abstract
Enantioselective hydrogenation of α-acetamidocinnamic (AACA) and itaconic (IA) acids has been studied on rhodium complexes {[Rh(COD)2]+TfO– + nMDPP}COD = 1,5-cyclooctadiene, nMDPP = (1S,2S,5R)-(+)-neomenthyldiphenylphosphine)] and {[Rh(S,S-DIODMA)2]+ TfO– + nMDPP} [(S,S)-DIODMA = 4S,5S-(+)-N4,N4,N5,N5,2,2-hexamethyl-1,3-dioxolane-4,5-dimethaneamine]. Addition of nMDPP decreases the activity of the catalyst and increases the optical yield with retention of the direction of stereoselection. Optical yields for hydrogenation on {[Rh(S,S-DIODMA)2]+TfO– + nMDPP} exceed those obtained on the diamine complex in the presence of Ph3P as well as those obtained on {[Rh(COD)2]+TfO– + nMDPP}. The result of combined action of two ligands may be considered as manifestation of `matched' effect. Transformations of complexes have been studied by the use of 1H and 31P NMR spectroscopy. At least three complexes exist in the catalytic system, namely, diamine complex [Rh(S,S-DIODMA)2]+TfO–, solvate complex [(nMDPP)2Rh(solv)2]+ TfO– and diamine-phosphine complex [(nMDPP)2Rh(S,S-DIODMA)]+ TfO–.
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