Study On Preparation And Catalytic Effect Of Carbonyl Metal Temperature-controlled Chiral Catalyst

Chirality is a natural property closely associated with our life.Asymmetric catalytic synthesis by chiral catalysts is the most effective method to obtain chiral compounds.However,chiral catalysts are not only extensive,but also difficult to be synthesized,and it is hard to be recycled and reused.Based on the flexible designability of ionic liquids,the recycling of noble metal catalysts in homogeneous reaction systems can be realized.Therefore,it has aroused much attention in recent years.In this thesis,a polyether carbonyl rhodium functionalized ionic liquid{[CH₃O（CH₂CH₂O）_nmim][Rh_x（CO）_y]}was synthesized via a three-step method including tosylation,iodination,and quaternization,and its structure was characterized by FT-IR and ¹H NMR.Besides,its physical properties（i.e.,melting point,viscosity,thermal stability,and solubility etc.）were also explored.The results indicated that active species[Rh_x（CO）_y]^-and ethoxy groups with temperature-controlled phase separation existed in the structure of{[CH₃O（CH₂CH₂O）_nmim][Rh_x（CO）_y]}.When n was 8 or 16,{[CH₃O（CH₂CH₂O）_nmim][Rh_x（CO）_y]}was liquid at room temperature,and when n was 22,{[CH₃O（CH₂CH₂O）_nmim][Rh_x（CO）_y]}melting point was 45-50℃ belonging to“room temperature ionic liquids”.Its viscosity increased with the increase of chain length of polyether chain,and its thermal decomposition temperature was²57℃,indicating it was stable in most carbonylation reactions.It was easily dissolved in polar solvents and does not show good solubility in non-polar solvents.However,it could be dissolved in the non-polar solvents cyclohexane and water.Based on its solubility properties,a temperature controlled two-phase catalysis system with mPEG400/1,4-dioxane/n-heptane as mixed solvent was designed and constructed,and the recycling of noble metal（Rh,Pd,and Pt）-based catalysts was realized.Secondly,chiral ligands BINAP and BINOL with asymmetric induction and controlfunctionwereintroducedtotheframeworkof{[CH₃O（CH₂CH₂O）_nmim][Rh_x（CO）_y]}via coordination to synthesize a new type of chiral ionic liquid,and its structure and physical properties were investigated in-depth.The results suggested that this chiral ionic liquid had good thermal stability with thermal decomposition temperature of ca.25℃;hence,it was stable in most carbonylation reactions.In addition,this chiral ionic liquid was also polar and soluble in water but insoluble in cyclohexane at 60 and 120℃,respectively.Under the optimal reaction conditions（toluene as solvent,P-tert-butyl catechol as inhibitor,BINAP as chiral ligand,reaction temperature=60℃,reaction time=4 h,P（CO/H₂=1）=2 MPa）,this chiral ionic liquid exhibited excellent catalytic performance in asymmetric hydroformylation reaction of styrene with styrene conversion of 84.9%,2-phenyl-propionaldehyde yield of 76%,and e.e.value of 69%.Finally,the reusability of chiral ionic liquid in above-mentioned temperature controlled two-phase catalytic system was investigated.The results indicated that this chiral ionic liquid could be recycled 5 times without distinct reduction of catalytic activity,suggesting it had good stability.Based on its excellent catalytic properties（catalytic activity and stability）,it might open up a new way for the separation and recovery of precious metals.