Ionic liquids have the advantage of immobilizing catalytic species and allow easy recycling of the catalyst phase (molecular complexes and metallic nanoparticles). The systems of metallic nanoparticles immobilized in ionic liquids exhibit dual reactivity, molecular and surface reactivity, depending on the reaction conditions.
To exemplify this, we can describe the immobilization of palladium nanoparticles (PdNPs) in an ionic liquid based on imidazolium which allow by a sequential way to catalyze the Heck coupling reaction followed by hydrogenation reaction (ChemCatChem 2009, 1, 244). In this process, molecular species of Pd are formed and are responsible for the Heck coupling; the hydrogen pressurization of the medium regenerates nanoparticles that provide the surface reactivity to promote the reduction of the coupling product, without need to isolate this intermediate. The use of a solvent of basic character, [EMI][HP(O)2OMe], avoids the addition of an external base and also prevents the use of hydrogen at high temperature (100 ° C) thanks to reductive nature of HP(O)2OMe-, (Phys. Chem. Chem. Phys. 2011, 13, 13579).
To go further on the non-toxicity solvent and low cost, we used glycerol as catalytic medium (Chem. Eur. J. 2014, DOI : 10.1002/chem.201403534). Also, the synthesis of organometallic complexes and stabilization of the nanoparticles can easily be carried out in this solvent, from biomass. For example, the Pauson-Khand reaction catalyzed by rhodium in glycerol (Eur. J. Inorg. Chem. 2013, 5138), is chemoselective and leads to higher yields than 90% of the desired product. A mechanistic study by NMR multi-cores was conducted and showed the coordinating glycerol behavior, appearance promoting carbocyclisation.
Also, nanoparticles of Pd and Cu2O were synthesized in glycerol, and applied in C-C bond and C-heteroatom formation reactions, hydrogenation, as well as in sequential and tandem process (Adv. Synth. Catal. 2013, 355, 3648 ; ChemCatChem. 2014, DOI : 10.1002/cctc.201402214).