Synthesis of a Novel β-Cyclodextrin-Functionalized Diphosphine Ligand and Its Catalytic Properties for Asymmetric Hydrogenation

Abstract

The novel diphosphine ligand 6A,6B-bis(diphenylphosphino)-6A,6B-dideoxy-permethylated-β-cyclodextrin (6A,6B-PMCDP2) has been prepared by reacting 6A,6B-dimesyl-permethylated-β-cyclodextrin (or 6A,6B-bis(trifluoromethanesulfonyl)-permethylated-β-cyclodextrin) with LiPPh 2 . A nine-bond P−P coupling of 10.2 Hz is observed for 6A,6B-PMCDP2. Treatment of 6A,6B-PMCDP2 with PtCl 2 (COD) and [Rh(COD) 2 ]BF 4 in dichloromethane produced PtCl 2 (6A,6B-PMCDP2) and [Rh(COD)(6A,6B-PMCDP2)]BF 4, respectively. The rhodium complex [Rh(COD)(6A,6B-PMBCDP2)]BF 4 is catalytically active for hydrogenation of α-acetamidocinnamic acid, α-acetamidoacrylic acid, itaconic acid, and their methyl esters with optical yields up to 92% ee.