Palladium nanoparticle catalysts in ionic liquids: synthesis, characterisation and selective partial hydrogenation of alkynes to Z-alkenes

The simple heating (120 °C) of Pd(OAc)2 in 1-butyronitrile-3-methylimidazolium-N-bis(trifluoromethane sulfonyl)imide ((BCN)MI·NTf2) under reduced pressure leads to the formation of stable and small-sized Pd(0)-NPs (diameter: 7.3 ± 2.2 nm). These metal nanoparticles were characterised by means of TEM, HRTEM and XPS analysis techniques. Moreover, the potential for partial hydrogenation of alkynes in multiphase systems was evaluated. The hydrogenation of internal alkynes at 25 °C and under 1 bar of hydrogen yields Z-alkenes (up to 98% selectivity). Application of higher hydrogen pressure (4 bar) in these reactions always led to the formation of alkanes without the detection of any alkenes. TOF values were attained up to 1282 h−1 with a good recyclability of the system which does not lose its activity for at least 4 runs.