Ligand effect on the catalytic activity of ruthenium nanoparticles in ionic liquids

Abstract

Suspensions of small sized (1–2.5 nm) ruthenium nanoparticles (RuNPs) have been obtained by decomposition, under H₂, of (η⁴-1,5-cyclooctadiene)(η⁶-1,3,5-cyclooctatriene)ruthenium(0), [Ru(COD)(COT)], in the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C₁C₄Im][NTf₂], and in the presence of different compounds acting as ligands: C₈H₁₇NH₂, PPhH₂, PPh₂H and H₂O. Previous and new liquid NMR experiments showed that the ligands are coordinated or in the proximity to the surface of the RuNPs. Herein is reported how the ligand affects the catalytic performance (activity and selectivity) compared to a ligand-free system of RuNPs, when RuNPs in [C₁C₄Im][NTf₂] are used as catalysts for the hydrogenation of various unsaturated compounds (1,3-cyclohexadiene, limonene and styrene). It has been observed that σ-donor ligands increase the activity of the nanoparticles, contrarily to π-acceptor ones.