Syntheses of Chiral Mutlidentate Ligands and Asymmetric Transfer Hydrogenation Catalyzed by Their Samarium Compounds

摘要

We synthesized chiral multi-dentate ligands(R)-l and(R)-2 suitable to support two metals cooperatively.The ligand(R)-1 was prepared from(R)-styrene oxide and m-xylylenediamine,while the phenoxy ligand(R)-2 was best synthesized by treating(lR,5R)-3-aza-l,5-dihydroxy-l,5-diphenyl pentane [(R)-5] and 2,6-bis(chloromethyl)-p-cresol(6).Asymmetric transfer hydrogenation of acetophenone was tested by Sm catalysts bearing multi-dentate ligands(R)-1 and(R)-2,the catalyst system based on(R)-! resulting in the high enentioselectivity(>99% ee)with moderate conversion(92%)for acetophenone reduction,being superior to the reported mononuclear samarium complex(R)-4 that afforded alcohol in 96% ee.