Functionalized Ionic Liquids for the Synthesis of Metal Nanoparticles and their Application in Catalysis

Colloidal suspensions of metal nanoparticles (NPs) in non-functionalized ionic liquids (ILs) are active catalysts for a wide variety of organic transformations. The weak ionic interaction between the IL and the metal surface provides a bare particle with a high concentration of active metal sites. However, the long-term stabilities can be affected as the IL cannot provide sufficient stabilization and aggregation of the NPs under catalytic conditions limits the reuse of NP:IL catalysts. ILs functionalized with a metal-binding moiety (FILs) can alleviate this agglomeration problem and provide catalysts with improved activities and recyclabilities. The enhanced stability is provided by the covalent attachment of the stabilizer to the metal surface, which holds the electrostatic stabilizing IL headgroup at the outer ligand sphere of the NP. FILs have been used in the synthesis of NPs as soluble ligands in aqueous, organic or IL solution, as neat solvents, as anchors to immobilize NPs onto a solid support and incorporated into polymeric stabilizers. This Minireview discusses the synthesis and application of NP:FIL systems, with an emphasis on catalysis.