Hydrogenation with rhodium complexes

The Influence of Potentially Bridging Groups in Homogeneous Hydrogenation with Rhodium Complexes A Study of para-Dimethylamino-Substituted Phenylphosphine Metal Complexes... 

Morimoto T, Chiba M, Achiwa K. Catalytic asymmetric hydrogenation with rhodium complexes of improved DIOPS bearing para-dimethylamino group on the basis of our designing concept. Tetrahedron Lett. 1988 29(37) 4755 758. 

For our initial studies we chose to evaluate the hydrogenation of two unsaturated carbonyl model prochiral substrates with rhodium complexes of chiral ferrocene diphosphine and tetraphosphine ligands using a standard set of conditions. The substrates screened were methyl a-acetamido cinnamate (MAC) and dimethyl iticonate (DIMI). The substrates, catalysts, conditions, and experimental results are shown in Table 1. 

Selke (58) for hydrogenation reactions with rhodium complexes containing these ligands. 

A review of asymmetric hydrogenation of ketones with rhodium complexes as catalysts has been presented.330 A review of the developments in the asymmetric hydrogenation of ketones with ruthenium complexes as homogenous catalysts of hydrogenation, with particular emphasis on the work of Halpern, has been presented.331... 

Removal of sulfur from these complexes remains challenging. Catalysts such as [M(COD)(PPh3)2]+ (M = Rh, Ir) only hydrogenate the C=C bond of benzothio-phene, whereas the hydrogenation with rhodium triphos complexes gives 2-ethyl-thiophenol.148 The addition of Co4(CO)i2 to (21-XXVIII, ML, = Cp Ir), however, leads to partial desulfurization, presumably with formation of cobalt sulfide.149... 

There are a number of reviews available on homogeneous hydrogenation. Specialized reviews are available on hydrogenation with phosphine complexes of rhodium, " on hydrogenation of arenas, on hydrogenation with water-soluble catalysts, " and on mechanistic aspects. There are general reviews covering the older and more recent literature. 

Catalytic asymmetric hydroboration has been most extensively studied with styrene (4) as the substrate which produces 1-phenylethanol (6) after treatment of the hydroboration product, l-phenyl-l,3,2-benzodioxaborole (5), with alkaline hydrogen peroxide (Scheme 2). The regioselectivity favoring the branched isomer 5 over the linear isomer 5 is usually high when the reaction is carried out with rhodium complexes coordinated with chelating ligands such as bisphos-... 

Two ruthenium complexes, binap 3.43-Ru(OCOR)2(R = Me,CF3) [892] and binap 3.43-RuX2 (X = Cl, Br, I) [893, 894], are quite useful. The acetate and trifluoroacetate complexes of 3.43 induce selective asymmetric hydrogenations of classes of prochiral olefins that are poorly selective with rhodium complexes. These classes include a,(3- or fcy-unsaturated acids and esters, ally alcohols, j3-acylaminoacrylates and enamide precursors of isoquinoline alkaloids [752, 853, 859, 881, 883, 895]. 

W. Knowles, M. Sabacky, B. Vineyard, D. Weinkauff, Asymmetric hydrogenation with a complex of rhodium and a chiral bisphos-phine, J. Am. Chem. Soc. 1975, 97, 2567-2568. 

Site-site interactions have been studied with rhodium complexes because of their importance as hydrogenation and hydroformylation catalysts. ds-Complexes were observed in IR spectra of macroporous resins f731. Equation 15 shows one example. Only a dimeric complex was observed in solution, tended X-ray absorption fine structure (EXAFS) spectra indicate that (polystyrylmethyl)diphenylphosphine forms two different complexes with RhBr(PPh3)3, depending on Ae degree of cross-linking (741. At high P/Rh ratios a dimeric structure was observed with a 2% cross-linked gel resin and 0.22 mmol of Rh/g, and a monomeric structure was observed with a macroporous 20% cross-linked resin and 0.14 mmol of Rh/g. 

Catalytic hydrogenations with ruthenium complexes have been reviewed. Another article deals with the intramolecular stereocontrol of hydrogenation reactions by functional groups in the substrate, and concentrates on the reduction of unsaturated alcohols, ketones, and esters by cationic rhodium and iridium complexes. A review on Enantioselective Synthesis with Optically Active Transition... 

A number of catalysts with the catalytic site in the dendrimer core has also been used in asymmetric hydrogenation. A rhodium complex with dendrimer diphos-phine with menthyl groups in its branches as a catalyst in acetamidocinnamic acid hydrogenation exhibited low enantioselectivity. For a catalyst where dendrimers were at the meta positions of phosphine, the reaction rate was substantially higher than that for a low molecular weight analogue and for a catalyst where dendrimers were at positions 2 and 5 of phosphine, the reaction rate was much lower [134-137],... 

Step 6 regenerates the hydrogen-bearing rhodium complex and reaction with another molecule of the alkene begins at step 3. 

Directed and Asymmetric Reduction The principles of directed and asymmetric reactions were first developed for hydrogenation, as discussed in Section 9.2. Asymmetric hydrosilation of ketones can now be carried out cata-lytically with rhodium complexes of diop (9.22). The new chiral ligand Et-duPHOS, made by Burk at du Pont, allows chiral amination of ketones via Eq. 14.50. Note how the use of the hydrazone generates an amide carbonyl to act as a ligand, as is known to favor high e.e. (see Section 9.2). Noyori s powerful BINAP ligand has been applied to a large number of asymmetric reactions. 

Pomelli et al. (156) reported a theoretical study using density functional methods to investigate how coordination of a CO2 molecule can assist in the release of formic acid from the catalyst complex in the last step of the catalytic cycle for the hydrogenation of CO2 with rhodium complexes. They find that the presence of a CO2 molecule in their active site model thermodynamically favors the formic acid dissociation from the complex and enhances the reaction rate. This may provide some additional explanation of the dramatic rate increases observed by Noyori and coworkers. 

Morrison JD, Burnett RE, Aguiar AM, Morrow CJ, Phillips C. Asymmetric homogeneous hydrogenation with rhodium (I) complexes of chiral phosphines. J. Am. Chem. Soc. 1971 93(5) 1301-1303. 

Hayashi, T., M. Tanaka, and I. Ogata Asymmetric Hydrogenation by Rhodium Complex with d-rrfl 5-l,2-bis-(Diphenylphosphinoxy)-cyclopentane as a Chiral Ligand. Tetrahedron I.etters 1977, 295. 

An early attempt to hydroformylate butenediol using a cobalt carbonyl catalyst gave tetrahydro-2-furanmethanol (95), presumably by aHybc rearrangement to 3-butene-l,2-diol before hydroformylation. Later, hydroformylation of butenediol diacetate with a rhodium complex as catalyst gave the acetate of 3-formyl-3-buten-l-ol (96). Hydrogenation in such a system gave 2-methyl-1,4-butanediol (97). 

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