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As shown by theoretical calculations, azabis(oxazoline)-copper complexes are considerably more stable than the analogous bis(oxazoline)-copper complexes. This enhanced stability allows them to be efficiently immobilized by means of electrostatic interactions to different anionic supports, such as clays and nafion-silica nanocomposites, without the loss of a ligand, as is observed for bis(oxazolines). As a result, enantioselectivities of around 90% ee are obtained in the cyclopropanation reaction between styrene and ethyl diazoacetate. Moreover, the solid catalyst is easily recoverable., This work was made possible by the generous financial support of the CICYT (project PPQ2002-04012), the MCYT and DAAD (Acción Integrada HA2001-0096), and the DGA. C.I.H. is indebted to the MCYT for a grant.

This workw as supported by the Fonds der Chemischen Industrie, the DAAD (Acción Integrada HA2001 – 0096), the C.I.C.Y.T. (project PPQ2002– 04012), the DGA, and through generous chemical gifts by Degussa AG. I.P. is indebted to the MEC for a grant.

Bis(oxazoline)–copper complexes, immobilised by electrostatic interactions on Laponite and Nafion/silica nanocomposites, have been tested as catalysts in the cyclopropanation of styrene with ethyl diazoacetate. Several factors play a decisive role in the outcome of the reaction. Firstly, the nature of the solid counterion is important, with perfluorosulfonic solids being the best in this regard. Secondly, the nature of the solvent used has a marked influence as some solvents cause the solid support to modify the stereochemical course of the reaction. Finally, the nature of the chiral ligand is also very important, in particular the strength of its copper complex, in order to avoid the formation of non-chiral catalytic copper centres. This particular effect has been highlighted by using a ligand that is able to give strong complexation, namely an iminobis(oxazoline) ligand, and this leads to the best enantioselectivities being obtained for reactions using electrostatically immobilised catalysts., This work was made possible by the generous financial support of the CICYT (project MAT99-1176) and the MCYT (Acción Integrada HA2001-0096). C.I.H. is also indebted to the MCYT for a grant.