Synthesis of New Chiral P, S Hybrid Ligands and Their Use in Asymmetric Hydrosilylation of Ketones

Novel chiral P, S-hybrid ligands bearing 1,2-cis phosphinomethyl (or thiomethyl) and thio (or phosphino) groups on a cyclopentane skeleton were prepared by using borane as a protecting group for the phosphino group. Asymmetric hydrosilylation of acetophenone with 1 mol% of rhodium complex catalysts prepared in situ from [Rh(COD)Cl]_2 and P, S ligands, (1R, 2R)-2-(diphenylphosphino)methyl-1-(phenylthio)cyclopentane (TPCP) and (1R, 2S)-1-diphenylphosphino-2-[(phenylthio)methyl]cyclopentane (PTCP) gave the corresponding alcohols. The asymmetric hydrosilylation with the ligand TPCP showed higher enantioselectivity than that with PTCP or a diphosphine ligand (1R, 2R)-1-(diphenylphosphino)-2-[(diphenylphosphino)methyl]cylopentane (PPCP).