Synthesis Of Zirconium Phosphonate-Supported Ru Catalysts And Application In The Asymmetric Hydrogenation Of Keto Ester

In this paper, using cheap and easily obtained L-(-)-phenylglycine as raw materials, we synthesized a series of phosphonates la-e (n=2-6) containing chiral amino alcohols with different organic arms length by several steps. The chiral amino alcohol group was covalently linked to the backbone of zirconium phosphonate structure through the hydrolysis of phosphonates la-e and precipitation with ZrOCl2 to obtain the zirconium phosphonate carriers 3a-e, which were easily dissolved in chloroform, dichloromethane, tetrahydrofuran and N, N-dimethyl formamide with the 110-142 mg/mL solubilities.The homogeneous transition-metal Ru chiral catalyst 4 were synthesized by the reaction of [RuCl2(p-cymene)] 2 with BINAP ligand. Then the supported homogeneous Ru chiral catalysts 5a-e were prepared by the immobilization of homogeneousl Ru chiral catalyst 4 onto the the pores of the backbone of zirconium phosphonate, which were also easily dissolved in chloroform, dichloromethane, tetrahydrofuran and N, N-dimethyl formamide with the 95.2-101.5 mg/ml solubilities. The supported homogeneous Ru chiral catalysts 5a-e were quantitatively recovered and reused from homogeneous reaction systems by the precipitation, filtration and dryness when the non-polar solvents such as petroleum and n-hexane were added.The structure, chemical composition and morphology of zirconium phosphonates 3a-e and the supported homogeneous Ru chiral catalysts 5a-e had been characterized by IR、TG、XPRD、TEM and N2 adsorption-desorption isothermal curve. The experimental results showed that 3a-e are a novel type of linear polymer carriers, which possessed the 50-60 nm line width with the mesoporous structure. Furtheremore, the supported homogeneous Ru chiral catalysts 5a-e are a kind of spherical particles with the diameters 60-80 nm and mesoporous structure.We examined the influence of the arms length (n=2-6) and different reaction conditions on the catalytic properties in the catalytic asymmetric hydrogenation of keto esters, and the 60-100% conversions of keto esters,40-94.4% yields and 50-74.5% e.e.. were obtained for the supported chiral catalysts 5a-e. It was found that the supported chiral catalysts 5a possessed the best catalytic properties and the optimum conditions were shown as follows:S-conformation of the BINAP ligand, 3 wt% of the loading ruthenium,400:1 molar ratio of substrate and catalyst,0.25 mol% catalyst,5 mol% p-toluenesulfonic acid dosage, dichloromethane/ethanol (v/v=1:1) as solvents,80℃,40 atm H2,1 h with stirring.