Example Of Asymmetric Hydrogenation Research Articles

Asymmetric Hydrogenation with Iridium C,N and N,P Ligand Complexes: Characterization of Dihydride Intermediates with a Coordinated Alkene

AbstractPreviously elusive iridium dihydride alkene complexes have been identified and characterized by NMR spectroscopy in solution. Reactivity studies demonstrated that these complexes are catalytically competent intermediates. Additional H2 is required to convert the catalyst‐bound alkene into the hydrogenation product, supporting an IrIII/IrV cycle via an [IrIII(H)2(alkene)(H2)(L)]+ intermediate, as originally proposed based on DFT calculations. NMR analyses indicate a reaction pathway proceeding through rapidly equilibrating isomeric dihydride alkene intermediates with a subsequent slow enantioselectivity‐determining step. As in the classical example of asymmetric hydrogenation with rhodium diphosphine catalysts, it is a minor, less stable intermediate that is converted into the major product enantiomer.

Asymmetric Hydrogenation with Iridium C,N and N,P Ligand Complexes: Characterization of Dihydride Intermediates with a Coordinated Alkene

Previously elusive iridium dihydride alkene complexes have been identified and characterized by NMR spectroscopy in solution. Reactivity studies demonstrated that these complexes are catalytically competent intermediates. Additional H2 is required to convert the catalyst-bound alkene into the hydrogenation product, supporting an Ir(III) /Ir(V) cycle via an [Ir(III) (H)2 (alkene)(H2 )(L)](+) intermediate, as originally proposed based on DFT calculations. NMR analyses indicate a reaction pathway proceeding through rapidly equilibrating isomeric dihydride alkene intermediates with a subsequent slow enantioselectivity-determining step. As in the classical example of asymmetric hydrogenation with rhodium diphosphine catalysts, it is a minor, less stable intermediate that is converted into the major product enantiomer.

The first example of asymmetric hydrogenation of imines with Co2(CO)8/(R)-BINAP as catalytic precursor

The first example of asymmetric hydrogenation of imines using Co2(CO)8/(R)-BINAP/H2/CO system was developed. The reaction conditions were screened with a wide range of N-aryl benzophenone ketimines, obtaining products with excellent yields and good enantiomeric excess. Moreover, a pathway is suggested based on the isolation and characterization of several catalyst intermediates.

Asymmetric Hydrogenation of Chiral Vinyloxazaborolidines under Ambient Conditions.

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Asymmetric hydrogenation of chiral vinyloxazaborolidines under ambient conditions

Novel homochiral vinyloxazaborolidines have been synthesized and subsequently hydrogenated using palladium on carbon under ambient conditions to produce, after oxidation of the boronate group, enantiomerically enriched secondary alcohols (up to 20% ee). Herein, the first example of asymmetric hydrogenation utilizing oxazaborolidines as chiral auxiliaries is reported.

Kinetic models for catalytic selection processes as applied to asymmetric hydrogenation

Kinetic terms for product formation in selection processes are evaluated for the example of asymmetric hydrogenation. The investigated models are characterized by preceding intermolecular equilibria to 2–4 stereoisomeric substrate complexes as well as direct intramolecular interconversion between corresponding diastereomeric intermediates. In the case of isobaric conditions the gross-hydrogen consumption can be described in each case by an equation analogous to simple Michaelis-Menten-type kinetics. The interpretation of the resulting constants is briefly demonstrated for a few practical examples. The temperature dependence of the enantiomeric ratio for the resulting products, as for example for a selection process, is also considered for the investigated models.