Chiral solid catalyst, its preparation and its use for the produ

Details Chiral solid catalyst, its preparation and its use for the produ Chiral solid catalyst, its preparation and its use for the produ

1998-07-13

1999-12-07

Dunn, Thomas

Chemistry of inorganic compounds

Miscellaneous process

502 62, 502 74, 560 1, 568700, 585 16, C01B 1100, C01C 1100, C01D 1100, C22B 1100

Patent

active

059978406

DESCRIPTION:

BRIEF SUMMARY
During the last decade, the utilisation of pure enantiomers in biology has increased exponentially, implying their economic importance. The search for methods to obtain pure enantiomers is given top priority by pharmaceutical and related companies.
Asymmetric hydrogenation is one of the most promising methods to obtain enantiomerically pure products. It has been widely investigated during the past decade. In general, two types of asymmetric hydrogenation catalysts can be distinguished: heterogeneous catalysts, based on metal (Ni, Pt)--loaded carriers (silica, alumina, . . . ) modified with chiral molecules and homogeneous transition-metals complexes. The second group of catalysts has superior properties as far as activity and enantioselectivity are concerned. The heterogeneous catalysts however are favourable from a technical and industrial point of view as they allow continuous operation and easy recovery and regenerability of the expensive catalysts.
Therefore, it is of utmost relevance to be able to develop chiral heterogeneous catalysts which possess the properties of transition metal complexes as far as activity and selectivity are concerned with both the technical and economic advantages of the heterogeneous systems.
Some attempts to synthesise this type of catalysts have been described in literature. A. Corma, M. Iglesias, C. del Pino, F. Sanchez, J.Chem.Soc.Chem.Commun., (1991). 1253-1255 developed an asymmetric hydrogenation catalysts based on a rhodium-complex, anchored on USY-zeolite via covalent bounding. The system suffers from the need for a relatively high temperature (65.degree. C.) and has only been described for the hydrogenation of dehydroamino-acid derivatives.
The immobilisation of di-rhodium complexes via covalent bounding on silica has been investigated for the hydrogenation of dehydroamino acid derivatives (A. Kinting, H. Krause, M. Capka, J.Mol.Catal., 33 (1985). 215-223, M. Eisen, J. Blum, H. Schumann, B. Gorella, J.Mol.Catal. 56 (1989). 329-337). Leaching of the catalytic complexes from the solid catalyst into the liquid phase could not be avoided. Moreover, the enantioselectivities obtained, are rather low. The hydrogenation of functionalised ketones has been carried out with a similar catalyst (J. F.Carpentier, F. Agbossou, A. Mortreux, Tertrahedron: Asymmetry. 6(1) (1995). 39-42). Low activity and enantioselectivity however are the important constraints of the system.
Another approach towards complex immobilisation is the use of ion exchangers with cationic or anionic complexes. R. Selke, K. Haupke, W. H. Krause, J.Mol.Catal., 56 (1989). 315-328 performed the hydrogenation of dehydroamino acid derivatives with high selectivity using a cationic rhodium complex, exchanged on a sulphonated resin. The system, however, lacks mechanical stability and is limited with respect to solvent choice.
The most versatile complexes in the field of asymmetric hydrogenations are the binap (2,2'bis(diphenylphosphino)-1,1'-binaphthyl))-based complexes (R. Noyori, Chem.Soc.Rev., 187 (1989)). Until now, only one successful attempt has been made to immobilise this type of complexes. K. T. Wan, M. E. Davis, J.Catal., 148 (1994). 1-8, K. T. Wan, M. E. Davis, Nature, 370 (1994). 449-450, K. T. Wan, M. E. Davis, J.Catal., 152 (1995), 25-30 developed a water-soluble analogue of binap by direct sulphonation. The ruthenium complex of this ligand is immobilised by the supported-aqueous-phase method. This technology basically uses two immiscible liquid phases (an aqueous phase and an organic phase). The catalyst is dissolved in the aqueous phase, whereas substrate and products are dissolved in the organic phase. To increase the contact area between both phases, the aqueous phase is adsorbed on a solid with a high specific surface area (third phase). The heterogenised complex catalyses the hydrogenation of 2-(6'-methoxy-2'-naphthyl) acrylic acid to naproxen, an anti-inflammatory agent. One of the main disadvantages of the system, however, is that sulphonation of the complex is required, which is difficult and

REFERENCES:
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Mikami et al., "Asymmetric Catalysis of Diels-Alder Cycloadditions by an MS-Free Binaphthol-Titanium Complex: Dramatic Effect of MS, Linear vs Positive Nonlinear Relationship, and Synthetic Applications", J. Am. Chem. Soc. 116, pp. 2812-2820, 1994.

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