Phosphines BPPFA

Rh complexes with ChiraPhos, PyrPhos, or ferrocenyl phosphines lacking amino alkyl side chains (such as BPPFA) are much less active toward tetrasubstituted olefins. Table 6-1 shows that in asymmetric hydrogenations catalyzed by 5a-d, the coordinated Rh complex exerts high selectivity on various substrates. It is postulated that the terminal amino group in the ligand forms an ammonium carboxylate with the olefinic substrates and attracts the substrate to the coordination site of the catalyst to facilitate the hydrogenation. 

The palladium-catalyzed coupling of silyl ketene acetals with aryl bromides in the presence of TlOAc has been applied to the asymmetric synthesis of 2-aryl-propionic acids (40—50% ee) by the use of BPPFA and several other chiral phosphine ligands (Scheme 2-16) [35]. 

In the 1970s and early 1980s the development of new catalysts was mainly based on new optically active chelating phosphines used in Wilkinson-type catalysts. This era of design and synthesis of optically active bidentate phosphines started in 1971 with Kagan s tartaric acid derived ligand DIOP [59, 60]. Successful and well-known examples followed, namely DIPAMP [62], prophos [63], chiraphos [64], BPPM [65], BPPFA [66], norphos [67], and BINAP [68]. A selection is depicted in Figure 3. 

The diphosphine (R,S)-BPPFA [(R,pS)-9] reacts analogously with acetic anhydride to give the corresponding acetate which can be derivatized. Replacement of the acetate by hydroxide leads to a useful ligand BPPFOH 1534, which has been used for the rhodium-catalyzed enantioselective reduction of a-oxo acids to a-hydroxy acids (Section D.2.3.1.). Recently, the chemistry of gold(I) complexes of such chiral phosphines has been developed they catalyze aldol-type cycloadditions of isocyanides to carbonyl compounds to give chiral dihydrooxazoles. which can be hydrolyzed to synthetically important chiral amino alcohols and amino acids 30,39,40. 

Recently, a novel type of chiral phosphines has been reported [43fl] which are very unique in that they have planar chirality. Representative examples are (S)kJc-[(/ )-2-diphenylphosphinoferrocenyl] ethyldimethylamine (PPFA), (R)-a-[(S)-2-dimethylphosphinoferrocenyl]ethyldimethylamine (MPFA), and (S)-a-[(R)-r,2-6w(diphenylphosphino)ferrocenyl] ethyldimethylamine (BPPFA), which were prepared by lithiation, followed by treatment with an appropriate diorganochlorophos-phine, of chiral a-dimethylaminoethylferrocene reported a few years before [436]. 

The cationic paUadium(II) complex [Pd(MeCN)2(PPh3)3](BF4)2 is an active catalyst for the hydroesterification of styrene using CO and methanol under very mild conditions. The catalytic system, Pd(Oac)-PPh3-p-toluenesulfonic (p-TsOH) could also produce the branched ester regioselectively in excellent yield at ambient temperature. The catalytic asymmetric hydroesterification of styrene by the use of chiral phosphines, such as (5)-l-[(l )-r,2-bis(diphenylphosphino)ferrocenyl]ethyldimethylamine, and (5)-(i )-BPPFA as ligands (Eq. 19). ... 

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