Optically active rhodium complexes with indenyl-linked phosphane ligands

Abstract

The optically active indenyl-linked phosphane ligands ( S)-[2-(3 H-inden-1-yl)-1-phenylethyl]diphenylphosphane ( L 1 ) and ( S)-[2-(4,7-dimethyl-3 H-inden-1-yl)-1-phenyl-ethyl]diphenylphosphane ( L 2 ) were synthesized in three steps from ( R)-1-phenylethane-1,2-diol in excellent yields. Their lithium salts reacted with [Rh(μ-Cl)(η 2-CH 2CH 2) 2] 2 at −78 °C in THF affording the planar chiral complexes ( S, R pl + S pl )-[Rh(η 5-indenyl-CH 2CH(Ph)PPh 2- kP)(η 2-CH 2CH 2)] and ( S, R pl + S pl )-[Rh(η 5-4,7-dimethylindenyl-CH 2CH(Ph)PPh 2- kP)(η 2-CH 2CH 2)] 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 L 2 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.