Rhodium optical resolution

Interesting examples of optical resolutions include the use of dicarbonyl-rhodium(i) 3-trifluoroacetyl-(li )-camphorate for g.l.c. separation of chiral olefins and of dimeric nickel(ll) bis-(3-trifluoroacetyl-li -camphorate) for an improved separation of chiral epoxides (cf. Vol. 8, p. 8). The resolution of (i /5)-pantoic acid with chiral amines derived from a- and jS-pinene (Vol. 7, p. 43, ref. 420) may signal their more widespread use. 1,3-Dithian 1-oxide has been resolved. ... 

A resolution of racemic CHIRAPHOS ligand has been achieved using a chiral iridium amide complex (Scheme 8.3). The chiral iridium complex (- -)-l reacts selectively with (S.S -CHIRAPHOS to form the inactive iridium complex 2. The remaining (R,R)-CHIRAPHOS affords the catalytically active chiral rhodium complex 3. The system catalyzes asymmetric hydrogenation to give the (5)-product with 87% ee. The opposite enantiomer (—)-l gives the (R)-product with 89.5% ee, which is almost the same level of enantioselectivity obtained by using optically pure (5,5)-CHlRAPHOS. 

After the resolution of 1-2-chloro-ammino-diethylenediamino-cobaltie chloride many analogous resolutions of optically active compounds of octahedral symmetry were carried out, and active isomers of substances containing central cobalt, chromium, platinum, rhodium, iron atoms are known. The asymmetry is not confined to ammines alone, but is found in salts of complex type for example, potassium tri-oxalato-chromium, [Cr(Ca04)3]K3, exists in two optically active forms. These forms were separated by Werner2 by means of the base strychnine. More than forty series of compounds possessing octahedral symmetry have been proved to exist in optically active forms, so that the spatial configuration for co-ordination number six is firmly established. 

T7fficient catalytic asymmetric hydrogenations have been achieved using an optically active phosphine complexed with rhodium (I, 2,3, 4, 5, 6, 7, 8). Through this process it is now possible to prepare a number of optically active a-amino acids from the corresponding unsaturated precursor without the usual resolution step by the following sequence. 

James et al. have applied this intramolecular hydroacylation to the resolution of racemic enals using rhodium(I) complex and chiraphos [103]. In this case, 5-membered ring ketones with up to 69% ee of the optical isomer are obtained in moderate yields (15-58% yields) (Eq.48). 

Average particle sizes were determined with TEM. For that purpose a drop of the colloidal solution was placed on a carbon covered copper grid (Balzers) and analyzed with a high resolution transmission electron microscope (model JEOL 200 CX). Particle size distributions were determined by optical inspection of the photographs. From this data, metal areas of the catalysts were estimated assuming spherical particle shape and a rhodium surface density of 1.66 10 mol Rh/m [10]. As a reference material for characterization and testing, a commercial rhodium on carbon catalyst (5w% Rh, Aldrich) was used. 

The present industrial processes used to produce the crucial intermediate (R)-(-)-pantolactone (22) are based on resolution of racemic material (3 ). A different and very promising approach has been reported by a Japanese group (26). Independently, Roche workers also investigated this approach which involves asymmetric reduction of ketolactone using rhodium catalysts derived from chiral phosphines (27 . In this manner, 22 can be obtained in very high chemical and optical yieldS ... 

The atropisomeric dinaphthophosphepins ( )-(35) (R = Me, Ph) can be prepared from 2,2 -dimethyl-l,r-dinaphthyl by lithiation and addition of the respective dichlorophosphine <94TA5ll, 94JOC6363>. The resolutions of ( )-(35) (R = Me, Ph) were accomplished by the method of metal complexation with use of an optically active ortho-metallated palladium(II)-amine complex. The absolute configuration of (S)-(—)-(35) (R = Ph) was determined from the x-ray crystal structure of (36). The optically active phosphepin in conjunction with rhodium(I) is an effective auxiliary for the asymmetric hydroformylation of styrene. 

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