Double Stereoselection in Hydrogenation of Prochiral Dehydrocarboxylic Acids on Rh(S,S-DIODMA)2+TfO – Complex in the Presence of (+)-Neomenthyldiphenylphosphine
a:2:{s:4:"TYPE";s:4:"TEXT";s:4:"TEXT";s:66:"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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