Inorganic — asymmetric catalysis
Noyori asymmetric hydrogenation
How the Noyori asymmetric hydrogenation works, in 3 steps. Each step shows the structures and the curved arrows that move the electrons.
In short. A 3-step mechanism. Typical reagents: RuCl₂[(R)-BINAP], H₂ (4–100 atm), substrate with directing group (β-keto ester). Conditions: MeOH or EtOH, 25–100 °C. Bonds formed: C–H; O–H (new stereocentre); bonds broken: H–H; C=O π. Stereochemistry: (R)- or (S)-BINAP selects the face; ee > 98% typical. Rate and selectivity: High turnover (TON up to 10⁵); chelation by directing group is key.
At a glance
Step 1: H₂ adds to Ru
A chiral Ru(BINAP) catalyst coordinates both H₂ (via oxidative addition, the same step covered much earlier) and the substrate's carbonyl or alkene through a directing group, in a well-defined chiral pocket set by the BINAP ligand's twisted geometry.
Step 2: Hydride delivered to one face
Migratory insertion delivers hydride to one specific face of the coordinated substrate — the chiral ligand environment makes one prochiral face dramatically more accessible than the other.
Step 3: Product released, catalyst regenerated
Reductive elimination-like release of the product regenerates the active catalyst — the combination of oxidative addition, insertion, and product release is mechanistically identical to Wilkinson's hydrogenation, with chirality added purely through the ligand's shape.
Abbreviations and terms
- R
- R group. Any carbon substituent (alkyl, aryl…) whose identity does not matter for the mechanism.
- MeOH
- Methanol. Polar protic solvent (also a nucleophile in solvolysis).
- EtOH
- Ethanol. Polar protic solvent.
- H2
- Hydrogen gas. Reductant for catalytic hydrogenation.
- Wilkinson
- Wilkinson’s catalyst, RhCl(PPh₃)₃. Homogeneous hydrogenation catalyst.
- BINAP
- 2,2′-Bis(diphenylphosphino)-1,1′-binaphthyl. Chiral bidentate phosphine for asymmetric catalysis.
- ee
- Enantiomeric excess. How much more of one enantiomer than the other is present.
How it compares with related reactions
| Noyori asymmetric hydrogenation | Asymmetric phase-transfer catalysis | Crabtree hydrogenation | |
|---|---|---|---|
| Reagents | RuCl₂[(R)-BINAP], H₂ (4–100 atm), substrate with directing group (β-keto ester) | Chiral cinchona-derived Q*⁺Br⁻ (1–10 mol%), 50% aq. KOH, glycine imine tBu ester, BnBr | [Ir(cod)(PCy₃)(py)]⁺ PF₆⁻, H₂ (1 atm) |
| Conditions | MeOH or EtOH, 25–100 °C | Toluene/CH₂Cl₂, 0 °C, vigorous stirring | CH₂Cl₂, 25 °C |
| Stereochemistry | (R)- or (S)-BINAP selects the face; ee > 98% typical | High ee: chiral ion pair shields one enolate face | Face selectivity set by the directing OH |
| Rate / selectivity | High turnover (TON up to 10⁵); chelation by directing group is key | Alkylation of the ion pair is rate-limiting | Alkene insertion/oxidative addition; works for tetrasubstituted alkenes |
Test yourself
Try to answer each question before opening it.
Which reagents and conditions are typical for the Noyori asymmetric hydrogenation?
RuCl₂[(R)-BINAP], H₂ (4–100 atm), substrate with directing group (β-keto ester). Conditions: MeOH or EtOH, 25–100 °C.
Which bonds are formed and which are broken?
Formed: C–H; O–H (new stereocentre). Broken: H–H; C=O π.
What is the stereochemical outcome?
(R)- or (S)-BINAP selects the face; ee > 98% typical
What controls the rate or the selectivity?
High turnover (TON up to 10⁵); chelation by directing group is key
Study guides that help with this reaction
- How to learn reaction mechanisms (without memorising everything)
- How to answer mechanism questions in an exam