Ruthenium asymmetric hydrogenation

Palmer and Wills in 1999 reviewed other ruthenium catalysts for the asymmetric transfer hydrogenation of ketones and imines [101]. Gladiali and Mestro-ni reviewed the use of such catalysts in organic synthesis up to 1998 [102]. Review articles that include the use of ruthenium asymmetric hydrogenation catalysts cover the literature from 1981 to 1994 [103, 104], the major contributions... 

Fig. 33. Examples of ruthenium asymmetric hydrogenations in the initial phase of the work ...

Fig.39. Ruthenium asymmetric hydrogenation of unsaturated carbonyl compounds...

Asymmetric hydrogenation has been achieved with dissolved Wilkinson type catalysts (A. J. Birch, 1976 D. Valentine, Jr., 1978 H.B. Kagan, 1978). The (R)- and (S)-[l,l -binaph-thalene]-2,2 -diylblsCdiphenylphosphine] (= binap ) complexes of ruthenium (A. Miyashita, 1980) and rhodium (A. Miyashita, 1984 R. Noyori, 1987) have been prepared as pure atrop-isomers and used for the stereoselective Noyori hydrogenation of a-(acylamino) acrylic acids and, more significantly, -keto carboxylic esters. In the latter reaction enantiomeric excesses of more than 99% are often achieved (see also M. Nakatsuka, 1990, p. 5586). 

BITIANP, were tested as ruthenium ligands for the asymmetric hydrogenation of various olefinic substrates. The results collected in Scheme 8.8 show that these novel ligands were able to induce high enantioselectivities of up to 94% ee. ... 

Several S/N ligands have also been investigated for the asymmetric hydrogenation of prochiral olefins. Thus, asymmetric enamide hydrogenations have been performed in the presence of S/N ligands and rhodium or ruthenium catalysts by Lemaire et al., giving enantioselectivities of up to 70% ee. Two... 

In addition, several S/S ligands were also investigated for the asymmetric hydrogenation of olefins. In 1977, James and McMillan reported the synthesis of various disulfoxide ligands, which were applied to the asymmetric ruthenium-catalysed hydrogenation of prochiral olefinic acid derivatives, such as itaconic acid. These ligands, depicted in Scheme 8.16, were active to provide... 

On the other hand, James reported, in 1976, the use of a chiral sulfoxide as a ligand of ruthenium for the asymmetric hydrogenation of itaconic acid, providing a low enantioselectivity of 12% ee (Scheme 8.23). ... 

In 2000, these authors also developed a very efficient diphosphine-bithiophene ligand, tetraMe-BITIOP, which is depicted in Scheme 8.29. The ruthenium complex of this electron-rich diphosphine was used as the catalyst in asymmetric hydrogenation reactions of prostereogenic carbonyl functions of a-... 

In recent years, the asymmetric hydrogenation of prochiral olefins have been developed in the presence of various chiral sulfur-containing ligands combined with rhodium, iridium or more rarely ruthenium catalysts. The best results have been obtained by using S/P ligands, with enantioselectivities of up to 99% ee in... 

In another context, chiral thioimidazolidine ligands have been successfully applied to the ruthenium-catalysed asymmetric hydrogen transfer of several aryl ketones by Kim et al., furnishing the corresponding chiral alcohols with high yields and enantioselectivities of up to 77% ee (Scheme 9.12). ... 

Manufacture of ruthenium precatalysts for asymmetric hydrogenation. The technology in-licensed from the JST for the asymmetric reduction of ketones originally employed BINAP as the diphosphine and an expensive diamine, DAIPEN." Owing to the presence of several patents surrounding ruthenium complexes of BINAP and Xylyl-BINAP, [HexaPHEMP-RuCl2-diamine] and [PhanePHOS-RuCl2-diamine] were introduced as alternative catalyst systems in which a cheaper diamine is used. Compared to the BINAP-based systems both of these can offer superior performance in terms of activity and selectivity and have been used in commercial manufacture of chiral alcohols on multi-100 Kg scales. 

Ruthenium complexes of (129) and (130)336 were investigated for the asymmetric hydrogenation of prochiral 2-R-propenoic acids (Scheme 62a) rhodium complexes of these ligands were used for hydrogenation of acetoamido-cinnamic acid methyl ester (Scheme 62c) and hydrogenation of acetophenone-benzylamine (Scheme 62b). The results obtained with these... 

ASYMMETRIC HYDROGENATION OF 3-OXO CARBOXYLATES USING BINAP-RUTHENIUM COMPLEXES (R)-(-)-METHYL 3-HYDROXYBUTANOATE (Butanoic acid, 3-hydroxy-, methyl ester, (R)-)... 

Other enantioselective reactions performed by microwave heating include asymmetric Heck reactions (Scheme 6.53 a) [109] and ruthenium-catalyzed asymmetric hydrogen-transfer processes (Scheme 6.53 b) [110]. 

Enantioselectivities in the range of 97.7-99.9%, with the majority in the range of 98.4-99.1%, are obtained in the asymmetric hydrogenation of aryl alkyl ketones with ruthenium catalyst 109.641 The same systems can hydrogenate /3-keto esters (95.2-98.6% ee) and a,/i-unsa(urated acids (96.2% in a single example).642... 

Asymmetric transfer hydrogenation can be employed in the asymmetric hydrogenation of prochiral ketones with a ruthenium complex of bis(oxazolinylmethyl) amine ligand 110. Enantioselectivities are greater than 95%.643... 

Figure 6.4. (Rj-BINAP ligands used in ruthenium catalysed asymmetric hydrogenation of dimethyl...

This appears to be the first asymmetric hydrogenation using a solvent as the hydrogen source. Closely related to this is the use of the ruthenium(II) catalysts Ru2C14(DIOP)3 (Section III,B) or RuCl2P3, where P is a chiral... 

The current research areas with ruthenium chemistry include the effective asymmetric hydrogenation of other substrates such as imines and epoxides, the synthesis of more chemoselective and enantioselective catalysts, COz hydrogenation and utilization, new methods for recovering and recycling homogeneous catalysts, new solvent systems, catalysis in two or three phases, and the replace-... 

Complexes containing one binap ligand per ruthenium (Fig. 3.5) turned out to be remarkably effective for a wide range of chemical processes of industrial importance. During the 1980s, such complexes were shown to be very effective, not only for the asymmetric hydrogenation of dehydroamino adds [42] - which previously was rhodium s domain - but also of allylic alcohols [77], unsaturated acids [78], cyclic enamides [79], and functionalized ketones [80, 81] - domains where rhodium complexes were not as effective. Table 3.2 (entries 3-5) lists impressive TOF values and excellent ee-values for the products of such reactions. The catalysts were rapidly put to use in industry to prepare, for example, the perfume additive citronellol from geraniol (Table 3.2, entry 5) and alkaloids from cyclic enamides. These developments have been reviewed by Noyori and Takaya [82, 83]. 

---