Homogeneous catalysts asymmetric

Asymmetric catalysis involving metal catalysed hydrogenations and isomerisations is becoming increasingly important in the production of pharmaceuticals, agrochemicals and flavours and fragrances. More examples of asymmetric homogeneous catalysts used are found in reference [3],... 

In the context of asymmetric catalysis, titanium silsesquioxanes containing the chiral ligand (lR,2S,5R)-(-)-menthoxo ligand (MentO) (figure 14.3) have been synthesized from the monosilanol la (R = cyclopentyl) and Ti(OPr )4 [70]. The molecular complexes were tested as asymmetric homogeneous catalysts for the epoxidation of cinammic alcohol with tert-butyl hydroperoxide and compared... 

Rh(COD)(/ ,/ -DIPAMP)]+BF4- (13) has shown remarkable activity and enantioselectivity in the asymmetric hydrogenation of various enamides, enol acetates, and unsaturated olefins.20 26 For the past 20 years, 13 has been the premier asymmetric homogeneous catalyst for amino acid synthesis, but a new generation of catalysts based on novel bisphosphines (vide infra) has surpassed it in versatility. 

Each industrial or potential scale-up process that uses BINAP-ligated asymmetric homogeneous catalysts has a common major drawback despite their respective high reactivities and enantioselectivities—the cost to produce the chiral ligand and limited availability. Until 1995, Takasago Co. has been the only indus-... 

Dehydroamino acids are important synthetic intermediates in that their reduction provides a route to a-amino acids. There has been a large volume of research examining the hydrogenation of such compounds, mediated by asymmetric homogeneous catalysts, to provide amino acids with varying degrees of optical purity. For example, a key step in an industrial procedure for the manufacture of l-DOPA is reported to involve the hydrogenation of (39) in the presence of the bisphosphine rhodium catalyst (40) to provide (41) in 94% optical yield (equation 21). 

Van Doorslaer S, Caretti I, Fallis lA et al (2009) The power of electron paramagnetic resonance to study asymmetric homogeneous catalysts based on transition-metal complexes. Coord Chem Rev 253 2116-2130... 

Structure 2.49 is a complex with a chiral Schiff base ligand and is probably the first example of an asymmetric homogeneous catalyst used in catalytic cyclopropanation reaction (see Section 7.5). The ligand in structure 2.50 is similar to SALEN but has two chiral centers. It has been used effectively as a chiral catalyst in some epoxidation reactions. 

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