Homogeneous and supported copper complexes of cyclic and open-chain polynitrogenated ligands as catalysts of cyclopropanation reactions

Cu-I and Cu-II complexes of cyclic and open-chain polyaza compounds have be en tested as catalysts in the benchmark cyclopropanation reaction of styren e with ethyl diazoacetate. In general, only small amounts of copper are nee ded to promote the reaction. The catalytic activity depends on the structur e of the ligand, e.g. amine-amides are more efficient than polyamines, and on the oxidation state of copper, Cu-II being more active than Cu-I. Given that Cu-I is the active species, these changes of behavior must be related to the stabilities of the complexes. The nature of the counterion also has a noticeable influence on the catalytic activity, the role of which is disc ussed. XAS measurements suggest the formation of oligomeric species. Some o f the chiral ligands lead to small enantiomeric excesses. Open-chain ligand s can easily be supported on organic polymers and their complexes can be us ed as catalysts. Furthermore, cyclic and acyclic complexes can be supported on clays by cation exchange and the solids obtained tend to promote the re action with a decrease in the trans/cis ratio.