Preparation Of Polyether Carbonyl Rhodium Chiral Catalyst And Its Application In Asymmetric Carbonylation

Asymmetric carbonylation reactions have been widely used in the synthesis of drugs,fragrances and natural products.However,precious metals and chiral ligands are difficult to separate and recover.Various methods have been developed to improve the recycling,such as water-organic biphase catalysis,fluorine biphase catalysis,thermally regulated phase transfer catalysis and biphase ionic liquid catalysis.However,the recovery of asymmetric hydroformylation catalysts is less studied.Ionic liquids have catalytic performance and recovery performance.Therefore,[R（EO）_nmim][Rh（CO）₄],[R（EO）_nTMG][Rh（CO）₄]and[（N-（EO）_nR）Py][Rh（CO）₄]were synthesized.The asymmetric hydroformylation reaction was catalyzed by chiral ionic liquids,and the process conditions were optimized.The reaction mechanism,separation and recovery of the catalyst were also studied.（1）In this paper,various polyether carbonyl rhodium ionic liquids were synthesized.In the first step,m PEG was used to react with CH₃SO₂Cl to obtain the intermediate.In the second step,the intermediate was quaternized with imidazole,tetramethylguanidine or pyridine to obtain ionic liquid.In the third step,[R（EO）_nmim][Rh（CO）₄],[R（EO）_nTMG][Rh（CO）₄]and[（N-（EO）_nR）Py][Rh（CO）₄]were synthesized by utilizing the ion exchange strategy.The above obtained ionic liquids were characterized by infrared（IR）and nuclear magnetic resonance（NMR）.The solubility of ionic liquids was also investigated.It could be completely dissolved in polar solvents,but in the non-polar solvents they were immiscible.（2）Chiral catalyst was prepared by utilizing situ coupling of[CH₃（EO）₁₆TMG][Rh（CO）₄]and BINAP for asymmetric hydroformylation of styrene.Under the conditions of methanol as solvent,pressure of 2 MPa,temperature of 60°C and 4 hours,the styrene conversion reached 79%and the 2-phenylpropanal yield reached 73.3%,e.e.of 54%.Chiral catalyst was prepared by utilizing situ coupling[(N-（EO）₁₆CH₃)Py][Rh（CO）₄]with BINAP for asymmetric hydroformylation of styrene.Under the conditions of methanol as solvent,pressure of 2 MPa,temperature of 80°C and 4 hours,the styrene conversion reached 87.8%and the 2-phenylpropanal yield reached 65.9%,e.e.of 57%.（3）The thermal stability of[Me（EO）₁₆TMG][Rh[（R）-Binap]（CO）₂],[(N-（EO）₁₆CH₃)Py][Rh[（R）-Binap]（CO）₂]chiral ionic liquids were analyzed by TG.The results showed that the initial decomposition temperature was higher than that of the asymmetric hydroformylation reaction.Therefore,the chiral ionic liquid could be used in the asymmetric hydroformylation reaction.The solubility of two kinds of chiral ionic liquids was investigated.Both of them could be completely dissolved in polar solvents,but in the non-polar solvents they were immiscible.Based on the solubility of two kinds of chiral ionic liquids,a homogeneous catalysis two-phase separation system was established.The recoverability of two kinds of chiral ionic liquids was investigated.When[Me（EO）₁₆TMG][Rh[（R）-Binap]（CO）₂]chiral ionic liquids were used,it could be reused for 4 times.When[(N-（EO）₁₆CH₃)Py][Rh[（R）-Binap]（CO）₂]chiral ionic liquids were used,it could be reused for 3 times,the reactivity had little change.The dissociation mechanism of the chiral catalyst was investigated by taking[Me（EO）₁₆TMG][Rh[（R）-Binap]（CO）₂]chiral ionic liquid as an example.The stable structure of[Me（EO）₁₆TMG][Rh[（R）-Binap]（CO）₂]ionic liquids with the lowest energy was simulated by density functional theory（DFT）.The energy is-9460.83 e V.The strong controllability and good stability of ionic liquids provide a new idea for the use of chiral ionic liquids catalysts.