Synthesis of Chiral, Monodentate Aminophosphane and Phosphoramidite Ligands Derived from Amino Acid Esters: Application in Rh-Catalysed Asymmetric Olefin Hydrogenation Reactions

Six chiral monodentate ligands combining a 1,3‐dioxa‐2‐phosphacycloheptadinaphthyl moiety [(R)‐ or (S)‐binoP] either with a phenylalanine‐ or with an alanine‐derived fragment were synthesised. The new phosphoramidites are all relatively air stable. Related compounds in which the binoP moiety was replaced by a diphenylphosphanyl group were also prepared for comparison. The X‐ray structures of two phosphoramidite complexes, cis‐PtCl2[(R)‐binoP–NMeR]2 [5, R = (R)‐CH(CH2Ph)(CO2Me); 6, R = (S)‐CH(CH2Ph)(CO2Me)], were determined by single X‐ray analysis. In the solid state, both structures are nearly C2 symmetric, and the nitrogen atoms lies out of the coordination plane. Owing to the particular orientation of the benzyl groups in 6, the environment of the coordination sites occupied in this complex by the chlorine atoms is sterically more crowded than in 5. In the hydrogenation of 2‐(acetylamino)‐3‐(aryl)propenoic methyl esters (aryl = 4‐X‐C6H4, X = H, F, Cl; aryl = 3,4‐Cl2–C6H3), the alanine‐derived phosphoramidites turned out to be ca. twice as active as the corresponding phenylalanine analogues. The highest ee's were observed with the phenylalanine derivatives, for example 92 % in the hydrogenation of 2‐(acetylamino)‐3‐(phenyl)propenoic methyl ester, by using (R)‐binoP–NMe‐(R)‐CH(CH2Ph)(CO2Me). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)