Asymmetric hydrogenation with the chiral clusters Rh4(CO)10[(-)-DIOP], Rh6(CO)10[(-)-DIOP]3 and related catalysts

R. Mutin*, W. Abboud, J. M. Basset, D. Sinou

*Corresponding author for this work

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14 Scopus citations

Abstract

The new chiral clusters Rh4(CO)10[(-)-DIOP] 1 and Rh6(CO)10[XXX] (XXX = (+)- or (-)-DIOP 2, (S,S)-chiraphos 3, (S)-peap 4) have been synthesized by ligand exchange from the parent clusters Rh4(CO)12 5 and Rh6-(CO)16 6. Assymetric hydrogenation of the methylester of Z-α-acetamido cinnamic acid has been carried out with the clusters 1-6, either alone or associated with n equivalents of (+)- or (-)-DIOP. Only for XXX = (+)- or (-)-DIOP an enantioselectivity is observed which depends mainly on the overall ratio DIOP/Rh. A maximum of activity and enantioselectivity (e.e. {all equal to} 60% R (-)) is achieved regardless of the precursor complex 1, 2, 5 or 6, provided the ratio (-)-DIOP/Rh is equal to or higher than unity. Spectroscopic studies indicate that the cluster 1 associated with 3 equivalents of (-)-DIOP undergoes a series of transformations which lead to Rh4(CO)8[(-)-DIOP]2 7 and [Rh(CO)[(-)-DIOP]]2 (μ-CO)2 8. 8 is the most abundant component, which oxidatively adds H2 reversibly at room temperature to give HRh(CO)2[(-)-DIOP] and related complexes. This mononuclear complex is the catalytically active component. Apparently the oxidative addition of H2 does not occur on the clusters 1, 2, 3, 4 but only on the zero-valent rhodium dimer 8 for which the P/Rh ratio is equal to unity.

Original languageEnglish (US)
Pages (from-to)47-59
Number of pages13
JournalJournal of Molecular Catalysis
Volume33
Issue number1
DOIs
StatePublished - 1985
Externally publishedYes

ASJC Scopus subject areas

  • Engineering(all)

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