The Construction Of Thermoregulated Phase-Separable Chiral Transition Metal Nanocatalytic System And Its Application In Asymmetric Hydrogenation

Transition metal nanocatalysts have been widely applied in catalytic reactions due to their outstanding reaction activity and selectivity.Nevertheless,how to realize the separation and reusability of the transition metal nanocatalysts still face challenges.Rencent years,along with the gereat demand of optical pure substances in industries of fine chemicals and pharmaceuticals,chiral catalysis has become a research hotspot.Then various chiral catalysts have been designed synthesis,among them,chiral transition metal nanocatalysts arouse the researchers great interest because of their simple preparation and excellent catalytic characteristics.Howerer,the separation and reusability of the costly chiral transition metal nanocatalysts are still difficult problem badly in need of solution.In this dissertation,a new type of chiral ionic liquid[CH3(OCH2CH2)nCD]+[CH3SO3]-(CD = cinchonidine,n = 12,16,22,42,113,shorted for CILPEG-CD)has been designed and synthesised.Through the electrosteric stabilization of the CILPEG-CD for transition metal nanoparticles,the chiral Pt,Ir,Rh,Ru,Pd and Au nanocatalysts were successfully prepared.In addition,the CILPEG-CD also exhibited a distinctive critical solution temperature(CST)property in the mixture of toluene and n-heptane.Thus,a thermoregulated phase-separable chiral transition metal nanocatalytic system has been constructed,which consists by the chiral transition metal nanocatalyst and the mixture of toluene and n-heptane.The characteristic of this system is depicted as follows:before reaction(T<CST),the lower chiral transition metal nanocatalyst phase is immiscible with the upper organic phase containing reaction substrate.However,in the reaction process(T>CST),the two-phase system turns into one-phase which allows the reaction to proceed homogeneously.After reaction(T<CST),the homogeneous system separates into two-phase again,namely the lower chiral transition metal nanocatalyst phase and the upper organic phase containing product.Therefore,the chiral transition metal nanocatalyst can be easily separated from the chiral product and directly reused.The thermoregulated phase-separable chiral Pt nanocatalytic system was applied into asymmetric hydrogenation of a-ketoesters,providing a series of chiral a-hydroxy ester compounds with up to>99%conversion and>99%ee under the optimized conditions.The chiral Pt nanocatalyst can be reused 8 times by simple phase separation with no loss in conversion and ee.In addition,the particle size of the chiral Pt nanoparticles basically remained unchanged between newly prepared and after 8 cycles.After each reaction of the cycling experiments,the Pt leaching in the upper organic phase was all below the detection limit.Till now,the study about the separation and reusability of the chiral Pt nanocatalyst in this reaction with high conversion and excellent ee has not been reported in the literatures.The thermoregulated phase-separable chiral Pt nanocatalytic system was applied into asymmetric hydrogenation of ?-keto acetals and ?-hydroxy ketones,providing a series of chiral ?-hydroxy acetal compounds and chiral 1,2-diol compounds with>99%ee under the optimized conditions.The chiral Pt nanocatalyst can be reused 4 times by simple phase separation with no loss in conversion and ee.In addition,the particle size of the chiral Pt nanoparticles basically remained unchanged between newly prepared and after 4 cycles.After each reaction of the cycling experiments,the Pt leaching in the upper organic phase was all below the detection limit.Till now,the study about the separation and reusability of the chiral Pt nanocatalyst in this reaction has not been reported in the literatures.The thermoregulated phase-separable chiral Ir-Rh bimetallic nanocatalytic system was applied into asymmetric hydrogenation of ?-keto acetals and ?-hydroxy ketones,providing a series of chiral ?-hydroxy acetal compounds and chiral 1,2-diol compounds with up to>99%ee under the optimized conditions.The chiral Ir-Rh bimetallic nanocatalyst can be reused 6 times by simple phase separation with no loss in conversion and ee.In addition,the particle size of the Ir-Rh nanoparticles basically remained unchanged between newly prepared and after 6 cycles.After each reaction of the cycling experiments,both Ir and Rh leaching in the upper organic phase were all below the detection limit.The catalytic performance of the chiral Ir-Rh bimetallic nanocatalyst was apparently superior to the sigle-metal Ir nanocatalyst(32%ee)and sigle-metal Rh nanocatalyst(80%ee).To our knowledge,studies on the chiral Ir-Rh bimetallic nanocatalyst for this reaction have not been repoted.