Thermoregulated Phase-Separable Pd Nanocatalyst For Selective Hydrogenation Of α,β-unsaturated Carbonyl Compounds At Atmospheric Hydrogen Pressure

Transition metal nanocatalysts have attracted much attention because of their high activity and selectivity.However,how to combine the above mentioned merits with the easy separation and recycling of the catalyst remains challenging.Based on previous work,in this paper ionic liquid[CH₃（OCH₂CH₂）₂₂N⁺Et₃][CH₃SO₃^-](IL_PEG1000)with critical solution temperature（CST）property was synthesized and used to stabilize Pd nanoparticles with average particle size of（3.4±0.2）nm.The Pd nanocatalysts stabilized by IL_PEG1000 exhibited thermoregulated phase-separable property in the toluene/n-heptane system.The principle of thermoregulated phase-separable catalysis was described as follows:At room temperature,the catalyst and the organic phase are immiscible.After rising to miscibility temperature,the two phases mixed into one phase.The sufficient contact between substrate and the catalyst is beneficial to the efficient catalytic reaction.After cooling to room temperature,the catalyst can be separated from the upper organic phase.The above-mentioned Pd nanocatalyst was employed for the selective hydrogenation ofα,β-unsaturated carbonyl compounds under atmospheric hydrogen pressure.Under optimized reaction conditions(p=1.01×10⁵ Pa（H₂balloon）,IL_PEG1000/Pd=100（molar ratio）,chalcone/Pd=500（molar ratio）,T=90℃,t=20 min),the conversion and hydrogenation selectivity of the C=C bond for chalcone were>99%.The catalyst can be easily separated from the product and recycled seven times remaining>99%conversion and selectivity.The turnover frequency（TOF）was up to 1470 h^-1,which exceeds the value reported in literatures for the selective hydrogenation of chalcone catalyzed by transition metal nanocatalysts under atmospheric hydrogen pressure.