Synthesis Of A Novel Thermoregulated Noyori Ligand Modified By Polyether And Its Application In Asymmetric Transfer Hydrogenation Of Acetophenone

In this paper, based on the concept of thermoregulated phase-transfer catalysis (TRPTC), a novel thermoregulated Noyori ligand modified by polyether has been designed and synthesized ,of which the structure was shown below.Using readily asscessible MeOPEG₅₅₀ (CH₃(OCH₂CH₂)_nOH,(?) =550) as starting material, the intermediate product sodium methoxyl polyethoxyl propanesulfonate was synthesized by the reaction with 1,3-propanesultone, which simplified the sysnthesis route of chiral ligand. The structure of synthesized novel Noyori ligand(MeOPEG-PsDPEN) was characterized by ¹H-NMR,¹³C-NMR and IR.This chiral ligand has the function of temperature-dependent water solubility-cloud point.In this study, complex catalyst formed in situ by [RuCl₂(p-cymene)]₂ with novel thermoregulated Noyori ligand modified by polyether (MeOPEG-PsDPEN) was used in the asymmetric transfer hydrogenation of acetophenone in aqueous/cyclohexane biphasic system. With sodium formate as a hydrogen source, various factors such as reaction temperature,reaction time,the amounts of sodium formate, the molar ration of substrate to catalyst and the amount of cyclohexane which effecting the activity and enantioselectivity were investigated. Results revealed that this catalyst remained high catalytic activity and enantioselectivity of Noyori catalyst, under the optimized reaction conditions of acetophenone:catalyst=100:1(molar ration) in 1.0 mL cyclohexane and 1.0 mL H₂O solution containing 3.0 mmol HCO₂Na at 30℃for 6 h, the conversion of acetophenone and the ee value ofα-phenylethanol were 100% and 94%, respectively. In this catalytic system, the product in organic phase and catalyst in aqueous could be easily separated by phase separation after reaction, and catalyst in aqueous could be reused five times without remarkable change of the enantioselectivity. The ee value of the product still kept 93% or so, but the conversion of the substrate gradually decreased to 19%.