Chiral metal complexes hydrogenation

A number of enantioselective hydrogenation reactions in ionic liquids have also been described. In all cases reported so far, the role of the ionic liquid was mainly to open up a new, facile way to recycle the expensive chiral metal complex used as the hydrogenation catalyst. 

Experimental evidence of the —S03" H0Si— interaction have been obtained from IR, Rh K-edge EXAFS, and CP MAS 3 IP NMR studies. These supported catalysts have been tested for the hydrogenation and hydroformylation of alkenes. No Rh leaching was observed.128-130 An extension to the immobilization of chiral metal complexes for asymmetric hydrogenation is reported below. 

Arylation, olefins, 187, 190 Arylketimines, iridium hydrogenation, 83 Arylpropanoic acid, Grignard coupling, 190 Aspartame, 8, 27 Asymmetric catalysis characteristics, 11 chiral metal complexes, 122 covalently bound intermediates, 323 electrochemistry, 342 hydrogen-bonded associates, 328 industrial applications, 8, 357 optically active compounds, 2 phase-transfer reactions, 333 photochemistry, 341 polymerization, 174, 332 purely organic compounds, 323 see also specific complexes Asymmetric induction, 71, 155 Attractive interaction, 196, 216 Autoinduction, 330 Axial chirality, 18 Aza-Diels-Alder reaction, 220 Azetidinone, 44, 80 Aziridination, olefins, 207... 

BINAP, 127, 171, 191, 194, 196 olefin reaction, 126, 167, 169, 191 organic halides, 191 Pancreatic lipase inhibitors, 357 Pantoyl lactone, 56, 59 para-hydrogen, 53 Peptides, matrix structure, 350 Perhydrotriphenylene, crystal lattice, 347 Pericyclic reactions, 212 chiral metal complexes, 212 Claisen rearrangement, 222 Diels-Alder, 212, 291 ene reaction, 222, 291 olefin dihydroxylation, 150 Phase-transfer reactions asymmetric catalysis, 333... 

The first industrially interesting production of a chiral pharmaceutical with a chiral metal complex catalyst is the asymmetric hydrogenation of cinnamic acid derivatives to give L-DOPA, see Fig. 6.21. 

Compared to CMP, the mechanism of separation on a chiral stationary phase is easier to predict, due to a much simpler system. Because the ligand is immobilized to a matrix and is not constantly pumped through the system, the detection limits for the enantiomers are much lower. Depending on the ligand immobilized to the matrix, one can have different types of interactions between the selectand and selector metal complexes, hydrogen-bonding, inclusion, tt-tt interactions, and dipole interactions, as well as a combination thereof. 

Kagan, H. B. Development of asymmetric catalysis by chiral metal complexes the example of asymmetric hydrogenation. C. R. lAcademie. Sci., Ser. lib Univers 1996, 322,131-143. 

Yoshikawa, K., Murata, M., Yamamoto, N., Inoguchi, K., Achiwa, K. Asymmetric reactions catalyzed by chiral metal complexes. III. The origin of the enantioselection in the ruthenium(ll)-catalyzed asymmetric hydrogenation of a,P-unsaturated carboxylic acid. Chem. Pharm. Bull. 1992, 40, 1072-1074. 

Y. Wang, J. Yu, Y. Li, and R. Xu, Chirality Transfer from Guest Chiral Metal Complexes to Inorganic Framework The Role of Hydrogen Bonding. Chem.-Eur. J., 2003, 9, 5048-5055. 

Catalytically active soluble chiral metal complexes containing a relatively cheap metal such as Co give interesting enantioselectivity in the hydrogenation of 1,2-diketones . Bio dimethylglyoximato Co(II) 3 (cobaloxime), associated with a cocatalyst and possessing a chiral amine function such as quinine, quinidine, cinchonidine, ephe-drine, brucine, or 5-( - )-a-methylbenzylamine, forms a chiral system that induces preferentially one enantiomer, as in enzymatic systems ... 

Asymmetric hydrogenation has been successfully achieved in this same type of media using [Rh(nbd)(DIOP)2]+ or [RuC12(BINAP)]2. NEt3 complexes as catalyst precursors (DIOP = 2,3-0-isopropylidene-2,3-dihydroxy-l,4-bis[diphenylphosphi-no]butane) [29, 32], In this case, NAILs open up a new and facile way to recycle the expensive chiral metal complex. 

On the other hand, if aluminosilicates are used as supports for chiral metal complex catalysts, they might reveal a contribution to asymmetric action as was found in the case of the hydrogenation catalyst [CoSalen] complex supported on hectorite... 

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