Selective Hydrogenation Of ?,?-unsaturated Aldehydes And Ketones Catalyzed By Thermoregulated Phase-separable Iridium Nanocatalyst

Transition metal nanocatalysts have been widely applied to catalysis due to their high catalytic activity and selectivity.However,similar to traditional homogeneous catalysts,separation of products from catalyst and recovery of the catalysts remains challenging.In this paper,thermoregulated phase-separable Ir nanocatalyst was prepared by reducing IrCl₃ with H₂ and using[CH₃?OCH₂CH₂?_nCD]⁺[CH₃SO₃]^-(CD=cinchonidine,n=16,shorted for CIL_PEG-CD750)as the stabilizer,which played the role of electrosteric stabilization.The Ir nanocatalyst and toluene/n-heptane mixed organic solvent construct the thermoregulated phase-separable catalytic system.The characteristic of the system is as follows:before reaction,the temperature is lower than the critical solution temperature?CST?,the reaction system was biphasic,namely the lower Ir nanocatalyst phase and the upper organic phase containing substrate;during the reaction,when the temperature was increased to certain point,higher than the CST,the biphasic system becomes miscible and turns into one phase,the reaction proceeds homogeneously at this time;after reaction,the temperature was cooled down to the temperature lower than the CST,the catalytic system turns to be biphasic phase again,namely the lower Ir nanocatalyst phase and the upper organic phase containing products.By easy phase separation,the Ir nanocatalyst can be separated from the product and directly reused in the next reaction run.The thermoregulated phase-separable Ir nanocatalyst was applied to the selective hydrogenation of different?,?-unsaturated ketones.Under the optimized conditions,the conversion of?,?-unsaturated ketones and the hydrogenation selectivity of C=C bonds were as high as>99%.For chalcone in the recycling experiments,the catalyst could be reused for five times and the selectivity of C=C bonds hydrogenation remained>99%.Moreover,the leaching of Ir in the upper organic phase was below the detection limit?the detection limit is5?g/L?.The thermoregulated phase-separable Ir nanocatalyst was applied to the selective hydrogenation of different?,?-unsaturated aldehydes.Under the optimized conditions,the conversion of?,?-unsaturated aldehydes and the hydrogenation selectivity of C=O bonds were as high as>99%.These results indicated that the Ir nanocatalyst exhibited high hydrogenation selectivity of the C=C bonds for?,?-unsaturated ketones,while high hydrogenation selectivity of the C=O bonds for?,?-unsaturated aldehydes.