Amino-phosphine ligands, catalyst

Garcia-Alvarez R, Diez J, Crochet P, Cadiemo V (2010) Arene-mthemijm(n) ctunplexes containing amino-phosphine ligands as catalysts for nitrile hydration reactions. Organometallics 29 3955... 

Hydrogenation catalysts. A number of new optically active phosphine ligands have been developed for selective enantioselective reduction of N=C bonds of amino acid precursors, including DPCB(l)1, the methylene homolog (2)2 of dipamp, and the novel ligand 3, in which the source of chirality is a Re atom.5 A ligand 4 has been used as a Rh(I) complex for hydrosilylation.4... 

Cleavage of imidazoles dehydroamino acids,3 2,4-Disubstituted imidazoles4 undergo a Diels-Alder-like reaction with singlet oxygen in the presence of DBU (1-2 equiv.) to provide imine diamides, which isomerize to dehydroamino acid derivatives in the presence of base. Hydrogenation in the presence of catalysts with chiral phosphine ligands results in optically active amino acid diamides. The overall process is illustrated for the synthesis of the N-benzylamide of N-acetylleucine (equation I). 

Asymmetric Hydrogenation Catalyst. Since catalytic asymmetric hydrogenation of a-acylaminoacrylic acid derivatives is an important process to afford a-amino acid derivatives, many rhodium complexes possessing optically active phosphine ligands have been developed in last two decades. [Rh (R)-(la) (cod)]Bp4 (2a) is one of the most efficient catalysts for this purpose with respect to activity and enantioselectivity. Besides (2a), several derivatives, which have various substituents on the nitrogen atom of the pyrrolidine ring, will be mentioned below. 

However, soluble metal chiral complex catalysts are better, even though ketone hydrogenation under these conditions is more difficult to run than olefin hydrogenation. Notable achievements have been made using Rh and Ru metals. Phosphine ligands are often used, which contain either an asymmetric alkyl group have the phosphorous atom as the asymmetric center, or have an axial element of chirality (atropisomerism) . Other chiral ligands commonly used are derived from amino acids, from L-hydroxyproline and from ferrocene. 

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