Asymmetric Hydrosilylation of Ketones Using Trans-Chelating Chiral Peralkylbisphosphine Ligands Bearing Primary Alkyl Substituents on Phosphorus Atoms

Asymmetric hydrosilylation of simple ketones with diphenylsilane proceeded at -40 °C in the presence of a rhodium complex (0.001—0.01 molar amount) coordinated with a trans-chelating chiral bisphosphine ligand bearing linear alkyl substituents on the phosphorus atoms, (R,R)-(S,S)-Et-, Pr-, or BuTRAP, giving the corresponding optically active (S)-secondary alcohols with up to 97% ee. The asymmetric hydrosilylation using TRAP ligands with bulkier P-substituents resulted in much lower enantioselectivities. The EtTRAP-rhodium catalyst was also effective for asymmetric hydrosilylation of keto esters with a coordination site for a rhodium atom (up to 98% ee). Optically active symmetrical diols were obtained with up to 99% ee from the corresponding diketones via the asymmetric reduction using 2.5 molar amounts of diphenylsilane.