BINAP ligands hydrogenation

Iridium(III) hydride forms complexes with DIOP, BDPP (2,4-bis(diphenyl-phosphino)pentane), NORPHOS, and BINAP ligands to produce amines in 11 -80% ee.679 Similar modest results are obtained in the reduction of N-arylketimines with an iridium(HI) complex with (2S,3 S) -C HIRA PHOS as the chiral ligand.680 The indium complexes with chiral phosphinodihydrooxazoles catalyze the enantioselective hydrogenation of imines in supercritical carbon dioxide with up to 80% ee, but generally lower ee values are observed in... 

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

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]. 

Lin et al. [106] studied the hydrogenation of yS-aryl ketoester using a ruthenium BINAP system with different substituents at the 4,4 -position of the BINAP ligand. The best enantioselectivities were achieved with steric demanding and electron-donating 4,4 -substituents. For example, ee-values of 97.2% and 99.5% were obtained for the hydrogenation of ethyl benzoylacetate with R=trimethylsilane (5,... 

Enantioselective catalytic hydrogenation. The ruthenium(II) complexes of (R)- and (S)-l, bearing a chiral BINAP ligand, catalyze asymmetric hydrogenation of N-acyl-l-alkylidenetetrahydroisoquinolines to give (1R)- or (lS)-tetrahydroiso-quinolines in 95-100% ee.1 Thus the (Z)-enamide (2), prepared by acylation of 3,4-dihydropapaverine, is hydrogenated in the presence of (R)-l to (1R)-tetrahydroisoquinolines (3). The enantiomeric (lS)-3 is obtained on use of (S)-l as catalyst. 

Soluble polymer-supported (i )-BINAP ligands were employed for the preparation of the Ru -bearing catalysts (54) and (55) which are shown in Scheme 4.33 [126]. Both these catalysts exhibited high activity and enantioselectivity in the asymmetric hydrogenation of 2-(6 -methoxy-2 -naphthyl)propenoic add. 

Wan and Davis135,138 modified rhodium complexes with the water soluble chiral tetrasulfonated binap ligand 26 (Table 2) and used them as catalysts in the asymmetric hydrogenation of 2-acetamidoacrylic acid in aqueous media. The e.e. observed in neat water using Rh/26 was approximately the same as that obtained with the unsulfonated Rh/binap in ethanol (68-70% versus 67%).135... 

Reaction Conditions versus Selectivity. [Rh(binap)(CH30H)2]C104 is an excellent chiral catalyst for asymmetric hydrogenation (13, 16). Scheme 5 relates the double bond geometry of the starting materials, the configuration of the BINAP ligand, and the stereochemistry of the products. The optical yield and the sense of asymmetric induction are... 

These results, obtained with chiral substrates, agree with the general sense of enantioselective hydrogenation of prochiral 3-oxo carboxylic esters. Obviously, the chirality of the BINAP ligand controls the facial selectivity at the carbonyl function, whereas cyclic constraints determine the relative reactivities of the enantiomeric substrates. Sterically restricted transition states that lead to the major stereoisomers are shown in Scheme 66. Overall, one of four possible diastereomeric transition states is selected to afford high stereoselectivity by dynamic kinetic resolution that involves in situ racemization of the substrates. 

Related ligands for catalysis, namely BINAP ligands substituted with Frechet dendrons (5, Fig. 6.34) were prepared by Chan et al. [51]. They form rutheniu-m(II) complexes in situ, whose activity in the stereoselective hydrogenation of 2-[p-(2-methylpropyl)phenyl]acrylic acid was investigated. 

The same group also developed optically active dendronized polymeric BINAP ligands (see also Sect. 5) as a new type of macromolecular chiral catalyst for asymmetric hydrogenation. They could be synthesized by condensation of 5,5 -diamino-BINAP with dendritic dicarboxylic acid monomers (Scheme 5) [44],... 

Fig. 17.79. Key intermediates in the enantioselective hydrogenations of Figure 17.76 (left). The BINAP ligand is shown schematically as U-shaped, with two PPh2 substituents. Ru-phosphine complexes undergo hydrogenation via Ru(II)/Ru(IV) intermediates, and the double bond of the substrate is hydrometatated in a monohydrido metal complex. Here, HeOH oxidatively adds to Ru(II) (I —> G), white it completes the ligand sphere of the metal Rh(I) in Figure 17.78.

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