Chiral bisphosphanes IX. Cationic rhodium(I)-complexes with (1S,2S)-cyclopentane-1,2-diyl-bis(dialkylphosphane)-ligands[(1S,2S)-C5H8(PR2)(2)Rh(1,5-COD)]O3SCF3: Syntheses, structures and catalytic applications

Radical-initiated P-H addition of (1S,2S)-C5H8(PH2)(2) (1) to allyl alcohol or 1,4-pentadiene produced the peralkylated chiral P-2 ligands (1S,2S)-C5H 8{P(C3H6OH)(2)}(2) (6) and (1S,2S)-C5H8(PC5H10-cyclo)(2) (7), respectively. Further P-alkylated bisphosphanes of the type (1S,2S)-C5H8(PR2)(2), where PR2 = P(C4H9-n)(2) (5) and P(C6H11-cyclo)(2) (8), were obtained from (1S,2S )-C5H8(PCl2)(2) (2) by Grignard substitution. Combination of (1S,2S)-C5H8{P (Cl)C8H15-cyclo}(2) (4) with CH3MgBr or of (1S,2S)-C5H8{P(H)C8H15-cyclo}(2) (3) with n-C4H9Li and CH3I afforded (1S,2S)-C5H8{P(CH3)C8H15-cyclo}(2) (9) as diastereomeric mixtures containing the S-P,S-P', R-P,R-P', and R-P,S-P' stereoisomers 9a-c in different proportions. The optically active chelate ligands 5-9 reacted with [Rh(1,5-COD)(2)]O3SCF3 to give cationic rhodium(I) complexes, [(1S,2S)-C5H8(PR2)(2)Rh(1,5-COD)]O3SCF3 [PR2 = P(C4H9-n)(2) (10 ), P(C3H6OH)(2) (11), PC5H10-cyclo (12), P(C6H11-cyclo)(2) (13) und P(CH3)C 8H15-cyclo (14)], of which 10, 13, and the R-P,R-P' diastereomer [(1S,2S)-C 5H8{P(CH3)C8H15-cyclo-(R)}(2)Rh(1,5-COD)]O3SCF3 (14a) were characterized by X-ray structure analysis. Use of these new complexes as catalysts in the h omogeneous enantioselective hydrogenation of alpha-acetamidocinnamic acid t o N-acetylphenylalanine provided optical yields varying between 6% and 77% e.e. The significant differences in the enantioselectivities observed with [(1S,2S)-C5H8{P(CH3)C8H15-cyclo-(R)}(2)Rh(1,5-COD)]O3SCF3 (14a) (33% e.e. o f S-(+)-N-acetylphenylalanine) and [(1S,2S)-C5H8{P(CH3)C8H15-cyclo-(S)}(2)R h(1,5-COD)]O3SCF3 (14b) (77% e.e. of R-(-)-N-acetylphenylalanine) are conti ngent upon the spatial orientation of the bulky cyclooctyl groups in the tw o diastereomeric cations.