Dendrimères modifiables par stimulation. Vers des catalyseurs adaptables – DENDSWITCH

It is generally admitted that 90% of the manufactured chemicals (including the medicinal products) result from catalytic reactions in at least one of the stages of their synthesis. In spite of (or because) of this universal use in industrial environment, there remains a very great place for the basic research in the field of catalysis. We propose to synthesize a new type, very original, of catalysts: dendritic catalysts with modifiable properties under the influence of an external stimulus (no currently known example). The dendritic catalysts can potentially combine the advantages and reduce the disadvantages of homogeneous and heterogeneous catalysts to the minimum. Indeed, they are soluble in solvents, they have a large well defined number of catalytic sites, and they can generally be easily separated from the products (and re-used) thanks to their large size. A relatively significant number of dendritic catalysts are already known, illustrating the increasing importance of this field of research. Some examples in which a synergy between the various catalytic entities linked to a dendrimer were reported. However, whole sections of catalysis were not explored up to now by using dendritic catalysts. It is in particular the case for ?switchable' catalysts (i.e. sensitive to an external stimulus). Some examples of stimulus-sensitive catalysts are known in monomeric form, and are currently the subject of an important research published in the best international scientific journals, but no example of this particular type of catalysts linked to a dendrimer is currently known. We thus propose to synthesize stimulus-sensitive and functionalized ligands (in Germany), then to graft these ligands on various dendrimers (in France), possibly by modifying their properties of solubility to make them water-soluble (in France), to study their complexation properties (in France and Germany), to check the persistence of the stimulus-sensitive properties (primarily in Germany) for finally using them in various types of catalyses (in Germany and France). These compounds ("molecular switches "), in which information is stored at the molecular level can adopt various modes of coordination. Their answer could be modified by the light, the pH, or electrochemically, or the external stimulus could be used to vary the steric properties, donor/acceptor properties (angle and steric request) and/or electronic. Their use to change the catalytic activity at will, to inhibit or activate catalysts, to start catalytic events, or to facilitate the recovery of catalyst will be tested. The German partner has an important knowledge and know-how on phosphines and switchable catalysis, while the French partner is specialized in the chemistry of the dendrimers. Their association will give a unique opportunity to combine for the first time stimulus-sensitive catalysts and dendrimers. The catalytic tests will be carried out partly in France, and for a greater part in Germany. In France reactions under atmospheric pressure will be tested, such as hydrations of alkynnes, isomerizations of alcohols, asymmetric hydrogen transfers, or C-C couplings. In Germany catalysis reactions under pressure will be carried out, in particular asymmetric hydrogenation reactions (important in industry), and hydroformylations. The types of stimuli applied will be in particular the UV-visible irradiation, electrochemistry (or chemical oxidation/reduction). The influence of the temperature and of microwaves will be tested also. Most promising reactions of catalysis, that is to say those for which using a switchable dendritic catalyst will bring improvements (lower temperature, better yield, lower pressure, regio- or enantio-selectivity, easier recycling of the catalyst, etc') will be studied more in details, including on the theoretical level (in Germany). Because of its originality and of its innovation, this project will be at the highest level of the fundamental research on the international level.