Selective Hydrogenation of 1,3‐Butadiene to 1‐Butene by Pd(0) Nanoparticles Embedded in Imidazolium Ionic Liquids

Abstract The reduction of Pd(acac) 2 (acac=acetylacetonate), dissolved in 1‐ n ‐butyl‐3‐methylimidazolium hexafluorophosphate (BMI⋅PF 6 ) or tetrafluoroborate (BMI⋅BF 4 ) ionic liquids, by molecular hydrogen (4 atm) at 75 °C affords stable, nanoscale Pd(0) particles with sizes of 4.9±0.8 nm. Inasmuch as 1,3‐butadiene is at least four times more soluble in the BMI⋅BF 4 than butenes, the selective partial hydrogenation could be performed by Pd(0) nanoparticles embedded in the ionic liquid. Thus, the isolated nanoparticles promote the hydrogenation of 1,3‐butadiene to butenes under solventless or multiphase conditions. Selectivities up to 97% in butenes were observed in the hydrogenation of 1,3‐butadiene by Pd(0) nanoparticles embedded in BMI⋅BF 4 under mild reaction conditions (40 °C and 4 atm of hydrogen at constant pressure). Selectivities up to 72% in 1‐butene were achieved at 99% 1,3‐butadiene conversion, 40 °C and 4 atm of constant pressure of hydrogen. The amounts of butane (fully hydrogenated 1,3‐butadiene) and cis ‐2‐butene products are marginal and the butenes do not undergo isomerisation process, indicating that the soluble Pd(0) nanoparticles possess a pronounced surface‐like rather than homogeneous‐like catalytic properties.