Synthesis of Co, Rh and Ir nanoparticles from metal carbonyls in ionic liquids and their use as biphasic liquid-liquid hydrogenation nanocatalysts for cyclohexene

Stable cobalt, rhodium and iridium nanoparticles are obtained reproducibly by thermal decomposition under argon from Co-2(CO)(8), Rh-6(CO)(16) and Ir-4(CO)(12) dissolved in the ionic liquids BMim(+)BF(4)(-), BMim(+)OTf and BtMA(+)NTf(2)(-) [BMim(+) = n-butyl-methyl-imidazolium, BtMA(+) = n-butyl-tri-methyl-ammonium, OTf = O3SCF3, NTf2- = N-(O2SCF3)(2)]. The very small and uniform nanoparticle size of about 1-3 nm in BMim(+)BF(4)(-) increases with the molecular volume of the ionic liquid anion in BMim(+)OTf and BtMA(+)NTf(2)(-). Characterization of the nanoparticles was done by transmission electron microscopy (TEM), transmission electron diffraction (TED), X-ray powder diffraction (XRPD) and dynamic light scattering (DLS). The rhodium or iridium nanoparticle/IL systems function as highly effective and recyclable catalysts in the biphasic liquid-liquid hydrogenation of cyclohexene to cyclohexane with activities of up to 1900 mol(product)/(mol(metal) h) and quantitative conversion within 1 h at 4 bar H-2 pressure and 75 degrees C. (C) 2008 Elsevier B.V. All rights reserved.