Homogeneous asymmetric catalysis

J. D. Morrison u. W. F. Master, Asymmetric Homogenous Hydrogenation, Advances in Catalysis, Vol. XXV,... 

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],... 

The catalyst is a combination of a chemo-catalyst and a natural product taken from the cinchona alkaloids giving amazing results. In phosphine catalysed asymmetric catalysis these types of structures are lacking, as nature does not produce phosphines ( ) and the phosphines used in the early years of development of asymmetric homogeneous catalysis lacked the complexity of... 

Asymmetric homogeneous catalysis generally requires chiral ligands. Approaches to chiral NHCs have focused on the generation of chiral centers either in the 4- and 5-position of imidazolidinium salts 71 or in the a-position of the nitrogen substituents for imidazolium salts 72. 

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... 

Weis, M., Waloch, C., Seiche, W. and Breit, B. (2006) Self-assembly of bidentate ligands for combinatorial homogeneous catalysis Asymmetric rhodium-catalyzed hydrogenation. J. Am. Chem. Soc.. 128. 4188-4189. 

Application of Molecular Orbital Theory to Catalysis Roger C. Baetzold The Stereochemistry of Hydrogenation of aj3-Unsaturated Ketones Robert L. Augustine Asymmetric Homogeneous Hydrogenation... 

The symmetry of the ligand can influence the product stereoselectivity and enantio-selectivity. Enantiomerically pure chemicals are extremely important for the agrochemical, pharmaceutical, and food industries. Many of the bidentate ligands used in these processes feature C2-type symmetry, dividing the space around the metal center into two empty quadrants and two full quadrants (see Section 3.1.3 on asymmetric homogeneous catalysis) [61,62], Ligand symmetry is also important in polymerization catalysis [63], where it can influence the polymer s tacticity (Figure 3.22). 

The second alternative is first to make the racemate, and then to resolve the desired enantiomer. However, such resolution is often time-consuming, laborious, and (for industry) very expensive. Conversely, asymmetric homogeneous catalysis gives access to a wide range of enantiopure organic substances from achiral precursors. The chiral catalyst complex directs the orientation of the substrate, giving preference... 

Although several enzymes can enantioselectively catalyze the hydrocyanation of R2C=0 and R2C=NR bonds [7], (asymmetric) hydrocyanation of C=C double bonds has no precedents in biology. In homogeneous catalysis asymmetric hydrocyanation is still underdeveloped, as is apparent from the relatively few reports in the literature. In the following paragraphs a short overview will be given divided into the two major substrate classes investigated, cyclic (di)enes and vinylarenes. 

Discussion on some asymmetric homogeneous catalytic reactions can also be found in Homogeneous Catalysis The Applications and Chemistry of Catalysis by Soluble Transition Metal Complexes, by G. W. Parshall and S. D. Ittel, Wiley, New York 1992. 

Unfortunately, no transition metal complex was synthesised, although the combination of a pendant OH functionality and chirality in the backbone of the imidazolidin ring holds great promise for asymmetric homogenous catalysis. 

The discovery of ferrocene and the establishment of its structure in the 1950s mark the beginning of modem organometallic chemistry. Today ferrocene chemistry is ubiquitous, and numerous significant applications are to be found in the areas of homogenous catalysis, asymmetric... 

Fache, R Schulz, E. Tommasino, M. L. Lemaire, M. Nitrogen-Containing Ligands for Asymmetric Homogeneous and Heterogeneous Catalysis, Chem. Rev. 2000,100,2091-2157. 

Syntheses of chiral 2,2 -bipyridines and 2,2 6 2"-terpyridines and their applications in asymmetric homogeneous catalysis 02CRV3129. 

Despite the explosion of asymmetric homogeneous catalysis technologies, very few have been able to make the jump from laboratory to manufacturing [10,17,18]. The focus of this chapter is to highlight and discuss the industrial feasibility of both old and new asymmetric hydrogenation technologies, as well... 

Although greater solubility in SCCO2 was observed with the borate (BArF) anion catalyst precursor than the triflate precursor, the more soluble precursor did not always give the greatest enantioselectivity. This article (60) was the first demonstration that asymmetric homogeneous catalysis could be performed in SCFs and the first demonstration that the technique could lead to greater enantioselectivity than that obtained in traditional solvents. 

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