Title : Cyclodextrins as a versatile tool for Organometallic catalytic processes
Abstract:
Green chemistry is a movement whose goal is to develop more environmentally friendly methods for the chemical industry. Use of (i) catalytic reagents and (ii) replacement of organic solvents are two of the main points of this movement. In this context, we proposed the use of cyclodextrins (CDs) family (i) as ligands for transition metals and (ii) as solvents for aqueous organometallic catalytic processes.
CD as ligands: In these processes, the catalyst is generally immobilized in water by water-soluble ligands such as phosphanes. These phosphanes are obtained by attaching water-solubilizing groups to known hydrophobic phosphanes. Among these groups, the CDs family is a very interesting class of hydrophilic block since phosphanes based on a CD skeleton can combine the molecular recognition and catalytic properties in the same entity. In this context, we reported the synthesis of new water-soluble cyclodextrin-phosphanes (CD-P). Organometallic complexes formed by these CD-phosphanes associated to a rhodium precursor are efficient in hydroformylation reaction. It is important to underline that the activity and selectivity of hydroformylation reaction can be tuned by the nature of the guest.
CD as solvents: Recently, a new family of solvents, so-called low melting mixtures (LMMs), have emerged in the current literature. In this context, LMMs based on N, N’-dimethylurea (DMU) and various β-cyclodextrins (CD) have been prepared for organometallic catalysis applications. These mixtures are easily obtained by simple association of CD and DMU around 90°C. These solvents are based on commercially available compounds and easily handled. These LMMs were evaluated as solvent in rhodium-catalyzed hydroformylation reaction and in palladium-catalyzed cleavage of allylcarbonates (Tsuji-Trost reaction). This solvent offered a simple handling and a protection of the catalytic species confined in the solvent at the solid state.
