Stable cobalt, rhodium and iridium nanoparticles are obtained reproducibly by thermal decomposition under argon from Co2(CO)8, Rh6(CO)16 and Ir4(CO)12 dissolved in the ionic liquids , BMim+OTf- and 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 increases with the molecular volume of the ionic liquid anion in BMim+OTf- and . 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 molproduct/(molmetal h) and quantitative conversion within 1 h at 4 bar H2 pressure and 75 °C.

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