The compounds [Co(acac)2], [Co(acac)3], [Fe(acac)3] and [Ni(acac)2] (acac = acetylacetonate) dissolved in 1-butyl-3-methyl imidazolium tetrafluoroborate (1), trifluoromethanesulphonate (2) or hexafluorophosphate (3) catalyze the reduction of 1,3-butadiene into butenes in a typical two-phase catalytic reaction. The 1,3-butadiene conversion, the selectivity and turnover frequencies (TOF) are strongly dependent on the nature of the transition metal catalyst precursor and the ionic liquid. For [Co(acac)2] dissolved in 1, kinetic studies strongly suggest that the reaction takes place in the ionic solution bulk, having an apparent activation energy for the overall process of 33.8 kJ mol-1. The recovered ionic catalyst solution can be reused several times without any significant changes on activity and selectivity.
biphasic hydrogenation; ionic liquids; dienes; cobalt catalysts
