Homogeneous Transition-metal Catalysis

Selective hydrogenation of 1,3-butadiene by transition metal compounds immobilized in 1-butyl-3-methyl imidazolium room temperature ionic liquids

“…This is a strong indication that the monomeric [Co(acac) 2 ] is transformed into an oligomeric structure. Indeed, spectroscopic studies of the ionic solution in the UV region showed a spectrum similar to those described in literature for [Co(acac) 2 Moreover, the recovered ionic catalyst solutions possess a light violet color. These observations can explain the observed reaction order (0.15 on [Co]), i.e., not all the cobalt centers are active species in the hydrogenation reaction.…”

“…In applications where only moderate selectivity is required heterogeneous catalysts excel due to their easy separability from reaction products by decantation or filtration, and the catalyst can be recycled. [1][2][3][4][5] Transition metal catalyst precursors are known to hydrogenate dienes to olefins under homogeneous conditions. 1,2 In these cases, however, C=C bond isomerization reactions are also operative decreasing the selectivity to hydrogenation products.…”

“…[1][2][3][4][5] Transition metal catalyst precursors are known to hydrogenate dienes to olefins under homogeneous conditions. 1,2 In these cases, however, C=C bond isomerization reactions are also operative decreasing the selectivity to hydrogenation products. 6 Moreover, the separation of the products from the reaction mixture and recovery of the catalyst represent disadvantages of these homogeneous catalytic reactions.…”

“…8 In these reactions, the catalysts maintain their molecular properties and achieve catalytic activities and selectivities similar to those obtained from the same catalyst precursors in homogeneous media. Indeed, oligomerization, [9][10][11][12] hydroformylation, 13 2 ], immobilized in 1-butyl-3-methyl imidazolium based molten salts are able to hydrogenate 1,3-butadiene into butenes in typical two-phase catalytic reactions under mild reaction conditions. Moreover, we present here kinetic and thermodynamic studies which evidence that, for the first time in this area, the reaction occurs preferentially in the ionic liquid catalyst solution.…”

“…All these results, associated with the selectivity, strongly suggest that the mechanism of the hydrogenation reaction for the cobalt complex dissolved in the ionic liquid is the same as in general accepted for cobalt cyanide complexes dissolved in water. 2 The influence of the nature of the ionic liquid on the hydrogenation of 1,3-butadiene by [Co(acac) 2 ] is shown in Table 2.From Table 2 it becomes evident that the catalytic activity is not significantly influenced by the nature of the non-coordinating anion of the ionic liquid whereas there is a dramatic change on selectivity. This behaviour can be related to the different solubility of 1,3-butadiene and the butenes in the ionic liquids.…”