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 ‐PtCl 2 [( R )‐binoP–NMeR] 2 [ 5 , R = ( R )‐CH(CH 2 Ph)(CO 2 Me); 6 , R = ( S )‐CH(CH 2 Ph)(CO 2 Me)], were determined by single X‐ray analysis. In the solid state, both structures are nearly C 2 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‐C 6 H 4 , X = H, F, Cl; aryl = 3,4‐Cl 2 –C 6 H 3 ), 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(CH 2 Ph)(CO 2 Me). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)