Formation of Trinuclear Rhodium-Hydride Complexes [{Rh(PP)H}3- (μ2-H)3(μ3-H)][anion]2-During Asymmetric Hydrogenation?

Recently described and fully characterized trinuclear rhodium‐hydride complexes [{Rh(PP*)H}3(μ2‐H)3(μ3‐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‐acetylaminocinnama...

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Bibliographic Details
Published in:Chemistry : a European journal 2013-06, Vol.19 (23), p.7443-7451
Main Authors: Kohrt, C., Baumann, W., Spannenberg, A., Drexler, H.-J., Gridnev, I. D., Heller, D.
Format: Article
Language:English
Subjects:
asymmetric hydrogenation
catalyst-substrate complex
Chemistry
hydrides
reaction mechanisms
rhodium
solvate complex
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Summary:Recently described and fully characterized trinuclear rhodium‐hydride complexes [{Rh(PP*)H}3(μ2‐H)3(μ3‐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}2(μ2‐H)3]BF4, [{Rh(DCPB)H}2(μ2‐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}2(μ2‐H)3]BF4) 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.
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.201204336