1- Cyclohexyl-3- rhodium

Closely related to the use of rhodium catalysts for the hydrogenation of phenols is their use in the reduction of anilines. The procedure gives details for the preparation of the catalyst and its use to carry out the low-pressure reduction of /j-aminobenzoic acid. Then, as in the preceding experiment, advantage is taken of the formation of a cyclic product to carry out the separation of a mixture of cis and trans cyclohexyl isomers. 

Ethane, (K)-l-cyclohexyl-L2-bis(diphenylphosphino)-rhodium complexes asymmetric hydrogenation, 6,253 Ethane, tetracyano-metal complexes, 2,263 Ethane, tetrakis(aminomethyl)-metal complexes, 2, 56 Ethane, tris[l, 1, l-(trisaminomethyl)]-complexes structure, 1,26... 

Phosphine, (2-bromophenyl)dichloro-, 2,991 Phosphine, (w-chloroalkyl)dichloro-, 2, 991 Phosphine, chlorodimethyl-, 2, 991 Phosphine, chloro(dimethylamino)-, 2, 991 Phosphine, chlorodiphenyl-, 2, 990 Phosphine, cyclohexyl(o-anisyl)methyl-rhodium complexes asymmetric hydrogenation, 6, 251 Phosphine, [(dialkylphosphino)alkyl]diphenyl-, 2, 994 Phosphine, dichloromethyl-, 2, 991 Phosphine, dichlorophenyl-, 2, 990 Phosphine, diethylphenyl-, 2, 992 Phosphine, dimethyl-, 2,992 Phosphine, dimethylphenyl-, 2,992 Phosphine, diphenyl-, 2, 992 Phosphine, ethyldiphenyl-, 2, 992 Phosphine, ethylenebis(diethyl-, 2, 993 Phosphine, ethylenebis(diphenyl-, 2,993 Phosphine, ethylenebis(phenyl-, 2,992 Phosphine, ethylidynetris[methylene(diphenyl-, 2,994 Phosphine, [(ethylphenylphosphino)hexyl]diphenyl-, 2, 994... 

Scheme 123 Reduction of cyclohexyl chloride to cyclohexyl radicals by rhodium (0).

Ketals of acetone and cyclohexanone with methyl, butyl, isopropyl and cyclohexyl alcohols are hydrogenolyzed to ethers and alcohols by catalytic hydrogenation. While platinum and ruthenium are inactive and palladium only partly active, 5% rhodium on alumina proves to be the best catalyst which, in the presence of a mineral acid, converts the ketals to ethers and alcohols in yields of 70-100% [933]. 

IrCl(PCy3)2 Chemistry and Dehydrogenation of a Cyclohexyl Ring. An investigation into the chemistry of IrCl(PCy3)2 species seemed warranted in view of the reactivity of the rhodium analogue (5, 12) and the IrCl(PPh3)2 species (34) toward small molecules. 

DAB (3) through efficient hydrogenation over rhodium on carbon.38 Similar paclitaxel and docetaxel analogues containing cyclohexyl groups were independently reported by Georg and coworkers.56... 

Rylander and Kilroy studied the formation of cyclohexyl phenyl ether intermediate in the hydrogenation of phenyl ether over binary platinum-rhodium oxide catalysts in cyclohexane at room temperature and atmospheric hydrogen pressure. The yield of the intermediate varied greatly with the catalyst composition. The highest yield (48%) was obtained over the catalyst consisting of 30% Pt-70% Rh.149... 

In order to study the hydrogenolysis in phenyl ether and its relationship to the formation of intermediates, Fukuchi and Nishimura hydrogenated phenyl ether and related compounds over unsupported ruthenium, rhodium, osmium, iridium, and platinum metals in f-butyl alcohol at 50°C and the atmospheric hydrogen pressure.151 The results are shown in Tables 11.11 and 11.12. In general, the greater part of the initial products as determined by an extrapolation method has been found to be cyclohexyl phenyl ether, phenol, and cyclohexane (Table 11.11). Over ruthenium, however, cyclohexanol was found in a greater amount than phenol even in the initial products. Small amounts of cyclohexyl ether, 1-cyclohexenyl cyclohexyl ether, cyclohexanol, cyclohexanone, and benzene were also formed simultaneously. 

The selectivity to cyclohexyl phenyl ether as a desorbed intermediate has also been determined by application of the equation in Scheme 11.7. In general, the selectivities obtained by both methods were in good accord. It is seen from the results that the selectivity to cyclohexyl phenyl ether decreases in the order Os > Rh > Ir > Pt > Ru. The yields of the ether at the maximum, however, are considerably lower than the corresponding selectivities with all the metals. The highest yield was obtained over rhodium (38.3%) rather than over osmium (29.0%), the metal of the highest selectivity for cyclohexyl phenyl ether, as the value of K was smaller over rhodium (0.37) than... 

Rylander and Hasbrouck hydrogenated acetophenone over supported rhodium catalysts at room temperature and atmospheric pressure. In general, higher maximum yields of cyclohexyl methyl ketone and 1-cyclohexylethanol were obtained over 5% Rh-Al203 than over 5% Rh-C. The highest yield of the saturated ketone (41%) and 1-cyclohexylethanol (99%+) were obtained over 5% Rh-Al203 in f-butyl alcohol.174... 

Nishimura and Kasai studied the hydrogenation of acetophenone in f-butyl alcohol using carefully prepared ruthenium and rhodium blacks.176 The selectivities for the formation of cyclohexyl methyl ketone and 1-phenylethanol as simultaneous products have been determined by application of the equation in Scheme 11.7. The values of K and/as well as the composition of the final products obtained are summarized in Table 11.13. Three ruthenium blacks—Ru (A), Ru (N), and Ru (B)—were prepared from the ruthenium hydroxide precipitated at pH 5,7, and 7.8, respectively, by adding lithium hydroxide solution to an aqueous solution of ruthenium chloride. It is seen that the selectivity for the saturated ketone (see figures in parentheses) was considerably higher over Ru (B) (43%) than over Ru (A) (25%) and Ru (N) (20%). The selectivity over Ru (N) increased markedly to 65% at 100°C and 5.9-7.8 MPa H2. Over rhodium... 

A number of groups have shown interest in the mechanism of asymmetric hydrogenation, principally of (a)-Z-acetamidocinnamic add and its derivatives. Kagan and co-workers have shown that cis addition of deuterium occurs to the Z isomer. Rhodium complexes of DIOP were used here. Koenig and Knowles obtained similar results with the ligands DIPAMP, cyclohexyl(o-... 

From the standpoint of applied research, the optimization of the rhodium catalyst (support and thermal pretreatment) and of reaction conditions (solvent, addition of amine) have led to a final d.e. of 68%, which is much higher than those obtained in our previous investigations and is encouraging for further studies in view of the difficulties to achieve the chiral synthesis of cyclohexyl derivatives. 

These considerations have been used to design new rhodium ligands [114, 115]. For instance, Achiwa and coworkers replaced the phenyl R groups of ligand 41 with cyclohexyl groups. The usefulness of the corresponding complexes is quite broad ( 7.1.1.1). 

Replacement of aryl rings by cyclohexyl groups has shown encouraging results. Achiwa and coworkers [114] recommended diphosphines 336 (R = c-CgHj j, Ar = Ph, R tart-BuO, MeO, MeNH) as ligands for rhodium in asymmetric hydrogenation of a,P-unsaturated acids 3.40 (Rg - R - H). The appropriate ketolactone precursor can also be reduced to (R)-pantolactone 1.16. 

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