Single step synthesis of metallic nanoparticles using dihydroxyl functionalized ionic liquids as reductive agent

Abstract

In the last few years, ionic liquids (ILs) have revealed their broad versatility for application towards the synthesis of shape and size controlled nanoscale metal catalysts, respectively metal(0) nanoparticles (M-NPs) in the absence of additive ligand. ILs play the role of solvent and ligand. In our work, we depict the synthesis of M-NPs (M = Cu, Ag, Ni, Ru) using dihydroxyl functionalized imidazolium ILs 1-(2,3-dihydroxypropyl)-2,3-dimethylimidazolium bis(trifluoromethanesulfonimide) [C₁C₁(EG)Im][NTf₂] as solvent, stabilizer and reductive agent simultaneously. In this IL the formation of stable dispersion of NPs from silver and copper salts in the absence of any reducing agent has been observed. The comparison of the ¹³C-NMR, and IR data of pure IL and IL–NP (Cu and Ag) suspensions proved the oxidation of the hydroxyl group to a carbonyl group, confirming that the dihydroxyl function of the IL acted as the reducing agent. This oxido-reduction depends on the nature of the metal. No reaction occurred with Ni^II and Ru⁰ precursors, and with Ru^II and Ni⁰ salts the formation of M-NPs is due to the activation of the acidic protons on the imidazolium ring. The Ru-NPs were then further evaluated for selective partial hydrogenation, here we observed good selectivities for α,β-unsaturated compounds such as cyclohexenone and cinnamic aldehyde, which can be converted exclusively into the unsaturated alcohols or saturated alcohols.