Influence of amines on the size control of in situ synthesized ruthenium nanoparticles in imidazolium ionic liquids

Very stable suspensions of small sized (c.a. 1.2 nm) and homogeneously dispersed ruthenium nanoparticles (RuNPs) were obtained by decomposition, under H-2, of (eta(4)-1,5-cyclooctadiene)(eta(6)-1,3,5-cyclooctatriene) ruthenium(0), [Ru(COD)(COT)], in various imidazolium derived ionic liquids (ILs: [RMIm][NTf2] (R = CnH2n+1 where n = 2; 4; 6; 8; 10) and in the presence of amines as ligands (1-octylamine, 1-hexadecylamine). These nanoparticles were compared to others stabilized either in pure ILs or by the same ligands in THF. NMR experiments (C-13 solution and DOSY) demonstrate that the amines are coordinated to the surface of the RuNPs. These RuNPs were investigated for the hydrogenation of aromatics and have shown a high level of recyclability (up to 10 cycles) with neither loss of activity nor significant agglomeration.