Nouveautés

More than thirty years after the discovery of practical asymmetric catalysis by Knowles and Kagan, the number of industrial processes using asymmetric catalysis is relatively small. This is mainly due to the high cost and often high toxicity of the organometallic complexes used as catalysts in homogeneous asymmetric catalytic processes. In most cases, the separation and the recycling of homogeneous catalysts from the bulk of the reaction are very difficult, if not impossible. Indeed, catalysis is largely used in production of chemicals where heterogeneous ones are generally preferred and 75% of these products (in weight) are synthesized via heterogeneous catalysis. Preparation and evaluation of heterogeneous asymmetric catalysts as efficient and selective as their homogeneous counter parts, began almost immediately after the discovery of practical asymmetric catalysis. We have used methodologies such as homogeneous supported catalysis and biphasic liquid-liquid catalysis, as well as ionic liquids and supercritical CO₂ in order to obtain efficient asymmetric catalysts which are both easy to separate and recycle. Bisoxazoline is one of the most useful ligands in asymmetric catalysis. Over the last few years, we have developed new materials based on bisoxazoline ligands grafted onto inorganic supports, such as silica. Control of the metal precursor and the surface (catalyst loading and silanol protection, etc.) allows the formation of catalysts with efficiency and selectivity similar to those obtained in solution. In addition, these catalysts can be recycled without decreasing either the conversion or the enantiomeric excess. Binap also has a wide range of applications, and are now produced on a hundred kilogram scale. Nevertheless, the modification of binap in order to make the separation and the recycling of the catalyst easier at the end of the reaction should improve the use of the catalyst prepared with this ligand. We have synthesized modified binap as selective as the binap itself, but included in a polymer main chain or soluble in water, an ionic liquid or supercritical CO₂. All these new processes show in our opinion that organic synthesis is not only the tool to create new useful molecules but may also contribute to solving actual environmental problems