Recovering Chiral Iridium Catalysts

  • Author: Li Grundl
  • Published: 04 March 2018
  • Copyright: Wiley-VCH Verlag GmbH & Co. KGaA
  • Source / Publisher: Advanced Synthesis & Catalysis/Wiley-VCH
thumbnail image: Recovering Chiral Iridium Catalysts

Chiral iridium complexes with N,P ligands are highly effective catalysts for asymmetric hydrogenation reactions. However, they are expensive for large-scale reactions and sometimes need high catalyst loadings. Although catalyst recovery is an active research field, the recovery of Ir catalysts has rarely been explored due to the instability of the catalytically active Ir complexes in the reaction medium.


Andreas Pfalz, University of Basel, Switzerland, and colleagues have developed a practical and simple protocol to recover Ir (N,P ligand) catalysts as stable COD [1,5-cyclooctadiene] complexes (pictured) from asymmetric hydrogenation reactions. The researchers used Ir(N,P ligand)(COD) complexes as precatalysts. The active species resulting from the reaction of this precatalyst with dihydrogen are too reactive to be isolated after use. Instead, the team added COD again at the end of the reaction, followed by a usual workup and chromatography. The more stable precatalysts could, thus, be recovered in 60–70 % yields with high purity.


The recovered catalysts show almost the same reactivity and enantioselectivity in asymmetric hydrogenation reactions as the original ones. Using NMR studies, the researchers found that dimeric Ir(III) dihydride complexes were formed after the reaction and COD could react with these dimers to regenerate the original precatalysts.


 

Article Views: 1750

Sign in Area

Please sign in below

Additional Sign In options

Please note that to comment on an article you must be registered and logged in.
Registration is for free, you may already be registered to receive, e.g., the newsletter. When you register on this website, please ensure you view our terms and conditions. All comments are subject to moderation.

Article Comments - To add a comment please sign in

If you would like to reuse any content, in print or online, from ChemistryViews.org, please contact us first for permission and consult our permisson guidance prior to making your request

Follow on Facebook Follow on Twitter Follow on YouTube Follow on LinkedIn Follow on Instagram RSS Sign up for newsletters

Magazine of Chemistry Europe (16 European Chemical Societies) published by Wiley-VCH