Optically active rhodium complexes with indenyl-linked phosphane ligands

The optically active indenyl-linked phosphane ligands (S)-2-(3H-inden-1-yl)-1-phenylethyl]diphenylphosphane (L₁) and (S)-2-(4,7-dimethyl-3H-inden-1-yl)-1-phenyl-ethyl]diphenylphosphane (L₂) were synthesized in three steps from (R)-1-phenylethane-1,2-diol in excellent yields. Their lithium salts reacted with Rh(μ-Cl)(η²-CH₂CH₂)₂]₂ at −78 °C in THF affording the planar chiral complexes (S,R_pl + S_pl)-Rh(η⁵-indenyl-CH₂CH(Ph)PPh₂-kP)(η²-CH₂CH₂)] and (S,R_pl + S_pl)-Rh(η⁵-4,7-dimethylindenyl-CH₂CH(Ph)PPh₂-kP)(η²-CH₂CH₂)] as 61:39 and 15:85 mixtures of diastereomers. The complexes were isolated in optically pure form by column chromatography. The stereochemical configuration of one of the diastereomers was determined by X-ray crystallography. The complexation of L₂ was studied in different solvents and with several Rh precursors and diastereomeric excesses up to 76% were achieved. The ability of the chiral ligands to control the stereochemistry at the metal center was tested by oxidative addition of methyl iodide. Diastereomeric excesses greater than 98% were observed.