Chiral bis(oxazoline) molecules coordinated to copper salts have been used in a range of catalytic C–C bond forming reactions. One major drawback is the high catalyst loading, often 10 mol %, that is frequently necessary.

Dorian Didier and Emmanuelle Schulz, University Paris-Sud, France, describe a process to recover and reuse these Cu catalysts. They used an anthracene-modified bis(oxazoline) ligand and Cu salt for ene and cyclopropanation reactions. To recover the catalyst, they added 2,4,7-trinitrofluoren-9-one to the reaction mixture. This immediately formed a charge-transfer complex with the anthracene-modified ligand which precipitated out of the solution.

The catalyst could be reused for up to ten successive catalytic cycles. The same catalyst batch was also successfully reused in three different asymmetric transformations in a multireaction procedure.

• Recycling Chiral Copper Bis(oxazoline) Complexes in an Original Multireaction Procedure
  D. Didier, E. Schulz,
  ChemCatChem 2011.
  DOI: 10.1002/cctc.201100250