Reversible microencapsulation of pybox–Ru chiral catalysts: scope and limitations

Chiral Pybox–Ru catalysts can be microencapsulated into linear polystyrene as a method to recover and recycle the valuable catalyst. These catalysts allow 60–68% yields to be achieved with enantioselectivities in the range 75–85% ee in the benchmark cyclopropanation reaction between styrene and ethyl diazoacetate. The catalyst is soluble in the reaction solvent and is re-encapsulated at the end of the reaction. The great advantage of this methodology is that the chiral ligand does not need to be modified, but the recycling is highly solvent dependent—in contrast with the catalysts immobilized through covalent bonds.