Recent Developments in Catalytic Asymmetric Hydrogenation Employing P-Chirogenic Diphosphine Ligands

• Published in: Advanced synthesis & catalysis 2003-01, Vol.345 (1-2), p.79-101
• Main Authors: Crépy, Karen V. L., Imamoto, Tsuneo
• Format: Article
• Language: English
• Subjects: C2-symmetry; catalysts; enantioselective hydrogenation; mechanism; P-chirogenic ligands; rhodium
• ISSN: 1615-4150; 1615-4169
• DOI: 10.1002/adsc.200390031

Rhodium‐ and ruthenium‐catalyzed asymmetric hydrogenations reactions employing C2‐symmetric chiral diphosphine ligands have a long history, and exceedingly high enantioselectivities have been reported. On the other hand, metal complexes containing P‐chirogenic, electron‐rich diphosphine ligands such as 1,2‐bis(alkylmethylphosphino)ethane (BisP*) and bis(alkylmethylphosphino)methane (MiniPHOS) have been tested only recently, and proved greatly successful. These results prompted intensive research amongst organic chemists, and the scope and limitations of the use of ligands bearing the chiral center at phosphorus atoms is presented in this review. The most recent data have been collected and summarized. In terms of ligand design, it is necessary to address an important question: “which properties are responsible for very high enantioselectivity in hydrogenation reactions?”. To this extent, a full discussion of new aspects on the mechanism, in particular the demonstration of a dihydride mechanism for enantioselective hydrogenation as opposed to the unsaturated mechanism widely accepted so far, also constitutes an important part of this review.