Rhodium complexes sulfates

Rhodium complexes with oxygen ligands, not nearly as numerous as those with amine and phosphine complexes, do, however, exist. A variety of compounds are known, iucluding [Rh(ox)3] [18307-26-1], [Rh(acac)3] [14284-92-5], the hexaaqua ion [Rh(OH2)3] [16920-31 -3], and Schiff base complexes. Soluble rhodium sulfate, Rh2(804 )3-a H2 0, exists iu a yellow form [15274-75-6], which probably coutaius [Rh(H20)3], and a red form [15274-78-9], which contains coordinated sulfate (125). The stmcture of the soluble nitrate [Rh(N03)3 2H20 [10139-58-9] is also complex (126). Another... 

Rhodium complexes of phosphinated glucopyranosides, [Rh(Me-a-glupOH)(cod)]BF4 and [Rh(Ph- -glup-OH)(cod)]BF4, reduced prochiral dehydroamino acid derivatives in water in the presence of surfactants [38, 39] addition of dodecyl sulfate increased both the rate and enantioselectivity of the hydrogenation, enantiomeric excesses up to 83% being obtained. The same trends were observed using [Rh(BPPM)(cod)]BF4 as the catalyst [40]. 

It was shown by Buriak and Osborn [80] that non-micelle-forming anions improved the enantioselectivity of an imine hydrogenation catalyzed by rhodium complexes in the same way as reverse micelles. Complexation of the sulfate or sulfonate anion with the catalyst appears to be responsible for the enhancement of the enantioselectivity. The very strong dependence of the product chirality on the structure of the anion is discussed. Finally, a long-chain ephedrinium salt 17 as surfactant, should be mentioned. 

Rhodium complex Hydroformylation Olefin+ Sodium n-dodecyl sulfate 7-120 > 79... 

The micellar effect in hydroformylation of 1-octene and 1-decene using water-soluble rhodium complexes with sulfonated diphosphanes in the presence of ionic surfactants and methanol in water was studied. The hydroformylation activities using cetyltrrmethylammonium hydrogen sulfate and methanol additives were found to be higher than those in experiments without these additives [101]. 

Despite the above similarities, many differences between the members of this triad are also to be noted. Reduction of a trivalent compound, which yields a divalent compound in the case of cobalt, rarely does so for the heavier elements where the metal, univalent compounds, or hydrido complexes are the more usual products. Rhodium forms the quite stable, yellow [Rh(H20)6] " ion when hydrous Rh203 is dissolved in mineral acid, and it occurs in the solid state in salts such as the perchlorate, sulfate and alums. [Ir(H20)6] + is less readily obtained but has been shown to occur in solutions of in cone HCIO4. 

Aqueous chemistry. This chemistry is almost exclusively that of complex compounds. Aquo ions of Ru11, Rum, Rh111 and Pd11 exist, but complex ions are formed in presence of anions other than CIO4, BFJ, or -toluene-sulfonate, etc. The precise nature of many supposedly simple solutions, e.g., of rhodium sulfate, is complicated and often unknown. 

O-Methylation of mandelic acid leads to the enantiomers of a-methoxy-M-phcnylacetic acid (10), which are also commercially available. This methylation without noticeable racemiza-tion was achieved with diazomethane, using aluminum tris(tert-butanoate) as catalyst8. Alternatively, dimethyl sulfate/ sodium hydroxide has been used15, as described in detail for the racemic compound10. The acids have been used for the construction of quite sophisticated chiral auxiliaries, e.g., a rhodium cyclopentadienyl complex (Section 7.2.2.), and for chiral dienes applied in both normal and inverse Diels-Alder reactions (Section D.1.6.1.1.1.). Chiral dienes, e.g., 1, for normal Diels -Alder reactions were prepared by pyrolysis (460 C) of a tricyclic precursor cstcrified with (S)-O-methylmandeloyl chloride or with the free acid and dicyclohexylcarbodiimide/4-dimethylaminopyridine11 -13. 

The phosphines of type (229) deserve special comment they are prepared by a simple but novel route from an optically active cyclic sulfate (Equation (54)). Some complexes based on a rhodium center have been found to have excellent enantioselectivity in hydrogenation reactions. 

Efficient asymmetric hydrogenation of (Z)-methyl a-acetamidocinnamate using chiral rhodium(I) complexes was first performed by Oehme and coworkers. Using N-tert-butoxycarbonyl-4-diphenylphosphino-2-diphenylphos-phinomehlyl-pyrrolidine (BPPM) and 4,5-bis(diphenylphos-phinomethyl)-2,2-dimethyl-l,3-dioxolane (DIOP) as ligands, they achieved their efficient solubilization in water in the presence of sodium dodecyl sulfate or of Triton X-100 amphiphiles, together with reaction rates and enan-tioselectivities comparable to those obtained as references in methanol without surfactants (Figure 6). ... 

Materials. The ultraviolet initiator Darocur 1173 (2-hydroxy-2-methyl-l-phenyl-propan-1-one) was purchased from EM Science and was used as received. Dimethylacrylamide (DMA), methacryloyl chloride (MC), allyloxytrimethylsilane and (tris(triphenylphosphine)rhodium)chloride were purchased from Aldrich Chemical Co. DMA and MC were distilled under nitrogen prior to use. 1,3-Tetramethyldisiloxane, methacryloylpropyltrichlorosilane, and 1,3-tetramethyldisiloxane platinum complex (2 % platinum in xylenes) were purchased from Gelest, The fluorinated allylic ether, allyloxy octafluoropentane, was prepared by the phase transfer catalyzed reaction of allyl bromide with octafluoropentanol using tetrabutylammonium hydrogen sulfate, tetrahydrofuran and 50% (w/w) NaOH (11). The fluorinated side-chain methacrylate end-capped siloxane (FSi) was prepared according to a literature procedure. All other solvents and reagents were used as received. 

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