Formation of trinuclear rhodium-hydride complexes [{Rh(PP*)H} 3- (μ2-H)33-H)][anion] 2 - During asymmetric hydrogenation?

C. Kohrt, W. Baumann, A. Spannenberg, H. J. Drexler, I. D. Gridnev, D. Heller

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13 Citations (Scopus)

Abstract

Recently described and fully characterized trinuclear rhodium-hydride complexes [{Rh(PP)H}32-H) 33-H)][anion]2 have been investigated with respect to their formation and role under the conditions of asymmetric hydrogenation. Catalyst-substrate complexes with mac (methyl (Z)- N-acetylaminocinnamate) ([Rh(tBu-BisP)(mac)]BF4, [Rh(Tangphos)(mac)] BF4, [Rh(Me-BPE)(mac)]BF4, [Rh(DCPE)(mac)]BF4, [Rh(DCPB)(mac)]BF4), as well as rhodium-hydride species, both mono-([Rh(Tangphos)- H2(MeOH)2]BF4, [Rh(Me-BPE)H2(MeOH)2]BF4), and dinuclear ([{Rh(DCPE)H}22-H)3]BF4, [{Rh(DCPB)H}22-H)3]BF4), are described. A plausible reaction sequence for the formation of the trinuclear rhodium-hydride complexes is discussed. Evidence is provided that the presence of multinuclear rhodium-hydride complexes should be taken into account when discussing the mechanism of rhodium-promoted asymmetric hydrogenation. Catalyst-substrate complexes containing the ligands tBu-BisP, Tangphos, Me-BPE, DCPE, DCPB, and mono- ([Rh(PP)(MeOH)2H2]BF4) or dinuclear ([{Rh(PP)H}22-H)3]BF 4) Rh-hydride species, are described (see figure). A sequence for the formation of the trinuclear Rh-hydride complexes is suggested. The presence of these complexes should be taken into account when discussing the mechanism of asymmetric hydrogenation.

Original languageEnglish
Pages (from-to)7443-7451
Number of pages9
JournalChemistry - A European Journal
Volume19
Issue number23
DOIs
Publication statusPublished - 2013 Jun 3

Keywords

  • asymmetric hydrogenation
  • catalyst-substrate complex
  • hydrides
  • reaction mechanisms
  • rhodium
  • solvate complex

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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