Chirale Bisphosphane IX, Kationische Rhodium(I)-Komplexe mit (1S,2S)-Cyclopentan-1,2-diyl-bis(dialkylphosphan)-Liganden, [(1S,2S)-C_5H_8(PR_2)_2Rh(1,5-COD)]O_3SCF_3: Synthesen, Strukturen und katalytische Anwendungen

摘要

Radical-initiated P-H addition of (1S,2S)-C_5H_8(PH_2)_2 (1) to allyl alcohol or 1,4-pentadiene produced the peralkylated chiral P_2 ligands (1S,2S)-C_5H_8{P(C_3H_6OH)_2}_2 (6) and (1S,2S)-C_5H_8(PC_5H_(10)-cyclo)_2 (7), respectively. Further P-alkylated bisphosphanes of the type (1S,2S)-C_5H_8(PR_2))2, where PR_2 = P(C_4H_9-n)_2 (5) and P(C_6H_(11)-cyclo)_2 (8), were obtained from (1S,2S)-C_5H_8(PCl_2)_2 (2) by Grignard substitution. Combination of (1S,2S)-C_5H_8{P(Cl)C_8H_(15)-cyclo}_2 (4) with CH_3MgBr or of (1S,2S)-C_5H_8{P(H)C_8H_(15)-cyclo}_2 (3) with n-C_4H_9Li and CH_3I afforded (1S,2S)-C_5H_8{P(CH_3)C_8H_(15)-cyclo}_2 (9) as diastereomeric mixtures containing the S_P,S_P, R_P,R_P, stereoisomers 9a-c in different proportions. The optically active chelate ligands 5-9 reacted with [Rh(1,5-COD)_2]O_3SCF_3 to give cationic rhodium(I) complexes, [(1S,2S)-C_5H_8(PR_2)_2Rh(1,5-COD)]O_3SCF_3 [PR_2 = P(C_4H_9-n)_2 (10), P(C_3H_6OH)_2 (11), PC_5H_(10)-cyclo (12), P(C_6H_11-cyclo)_2 (13) und P(CH_3)C_8H_(15)-cyclo (14)], of which 10, 13, and the R_P,R_P diastereomer [(1S,2S)-C_5H_8{P(CH_3)C_8H_(15)-cyclo(R)}_2Rh(1,5-COD)]O_3SCF_3 (14a) were characterized by X-ray structure analysis. Use of these new complexes as catalysts in the homogeneous enantioselective hydrogenation of #alpha#-acetamidocinnamic acid to N-acetylphenylalanine provided optical yields varying between 6% and 77% e.e. The significant differences in the enantioselectivities observed with [(1S,2S)-C_5H_8{P(CH_3)C_8H_(15)-cyclo-(R)}_2Rh(1,5-COD)]O_3SCF_3 (14a) (33% e.e. of S-(+)-N-acetylphenylalanine) and [(1S,2S)-C_5H_8{P(CH_3)C_8H_(15)-cyclo-(R)}_2Rh(1,5-COD)]O_3SCF_3 (14b) (77% e.e. of R-(-)-N-acetylphenylalanine) are contingent upon the spatial orientation of the bulky cyclooctyl groups in the two diastereomeric cations.