Ruthenium , chiral “binap” complexes

Rose Bengal xanthene dye photosensitizer, 277 Ruthenium, dihydrotetrakis(triphenylphosphine)- double bond shift in alkenes, 270 Ruthenium(2 +), chiral binap complexes asym. hydrogenation with, 102-103, 325-326 Ruthenium(8 +) oxide oxidation with of alcohols to ketones (catalytic), 267 of alkynes to 1,2-diones (catalytic), 117, 132 of ethers to esters, 118, 134-135... 

Reduction of unsaturated carboxylic adds gives products that you might alternatively think of making by auxiliary-controlled alkylation methods. When the NutraSweet company needed this chiral branched carboxylic acid as a single enantiomer, they initially used the auxiliary methods of p. 1110 to make a small amount, but they found that ruthenium-catalysed hydrogenation was greatly to be preferred on a large scale just 22 g of the ruthenium-(5)-BINAP complex is needed to produce SO kg of product with 90% ee. 

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. 

Diketone 5 is reduced to diol 23 by the method of Noyorv hydrogenation with catalysis by the chiral ruthenium-BINAP complex [(S)-BINAP]RuCE 2-NEt ... 

Milestones in the development of the diphosphane family include the establishment of BINAP [10] and DuPHOS [11]. The potential offered by the chiral diphosphane complexes of ruthenium [12] and iridium [13] in hydrogenation was also recognized. In parallel inves-... 

The chiral structure of BINAP enables highly enantioselective reactions in organic synthesis. The Ru- and Rh-BINAP complexes catalyze the hydrogenation of functionalized alkenes and carbonyls on only one face of the molecule. For example, asymmetric hydrogenation of methyl 3-oxobutanoate (1.58) using (R)-BINAP-ruthenium complex yields (R)-(—)-methyl 3-hydroxybutanoate (1.59) in 99.5% ee °. 

Asymmetric lactonization of prochiral diols has been performed vsdth chiral phosphine complex catalysts (Ru2Cl4((-)-DIOP)3 and [RuCl((S)-BINAP)(QH6)]Cl [17, 18]. Kinetic resolution of racemic secondary alcohol was also carried out with chiral ruthenium complexes 7 and 8 in the presence of a hydrogen acceptor, and optically active secondary alcohols were obtained with >99% e.e. (Eqs. 3.7 and 3.8) [19, 20]. 

Ruthenium(II) complexes may also be used to oxidize N-Boc hydroxylamine in the presence of tert-butylhydroperoxide (TBHP) to the corresponding nitroso dieno-phile, which is subsequently trapped by cyclohexa-1,3-diene to give the hetero Diels-Alder adduct (Entry 1, Scheme 10.26) [51]. A triphenylphosphine oxide-stabilized ruthenium(IV) oxo-complex was found to be the catalytically active species. Use of a chiral bidentate bis-phosphine-derived ruthenium ligand (BINAP or PROPHOS) result in very low asymmetric induction (8 and 11%) (Entry 2, Scheme 10.26). The low level of asymmetric induction is explained by the reaction conditions (in-situ oxidation) that failed to produce discrete, stable diastereomerically pure mthenium complexes. It is shown that ruthenium(II) salen complexes also catalyze the oxidation of N-Boc-hydroxylamine in the presence of TBHP, to give the N-Boc-nitroso compound which can be efficiently trapped with a range of dienes from cyclohepta-1,3-diene (1 h, r.t., CH2CI2, 71%) to 9,10-dimethylanthracene (96 h, r.t., CH2CI2,... 

The first reported example using macromolecule-supported catalysts in latent biphasic systems was work by Chan s group that employed a dendrimer-bound BINAP 127 that was used to form a chiral ruthenium hydrogenation catalyst [164]. The dendritic Ru-BINAP complex formed from the reaction of [RuCl2(benzene)2]2 and 127 was successfully used in four cycles in the hydrogenation of 2-phenylacrylic acid (Eq. 65) in a 1 1 (vol/vol) ethanol/hexane mixture. Addition of 2.5 vol% water to this mixture produced a biphasic mixture where >99% of the dendritic catalyst was in the hexane phase. Addition of a fresh ethanolic substrate solution to this hexane phase produced another miscible solution of catalyst and substrate. The second and subsequent cycles of hydrogenation carried out in this manner led to consistent conversions of substrate with synthetic yields of >91% with e.e. values of 90%. 

Among the vast number of chiral homogeneous catalysts, rhodium(I) and ruthenium(II) diphosphane complexes revealed to be the most efficient ones in asymmetric hydrogenation of functionalized olefins of practical importance. In certain cases described below (including also the BINAP-containing systems), enzyme-like enantioselectivities matching the requirements of natural product synthesis were reported. 

This technique employs a chiral catalyst and can be used to prepare amino acids with very high enantiomeric excess (% ee). Many of the chiral catalysts that have been developed contain a ruthenium atom (Ru) complexed to a chiral figand, such as BINAP. 

Another example of the application of DFT-based calculations comes from ruthenium catalyst-based asymmetric hydrogenations of ketones. As shown in Figure 3.5, the rra 5-dihydride complex 339 with chiral BINAP as the ligand is the resting state of the catalyst. Catalysis with 339 is proposed to occur by the transfer of a hydride from the ruthenium and a proton from the amine to the carbonyl group of the substrate, e.g., acetophenone. 

The mechanism of the hydrogenation of a,j -unsaturated carboxylic acids by chiral ruthenium BINAP complexes has been investigated (Scheme 5). The rate-limiting step in methanol at near-ambient temperature is the activation of H2 to give a anionic hydrido complex. The reaction is sensitive to strong acids one equivalent CF3SO3H per Ru prevents catalysis, while base has no effect. Over 90% enantiomeric excess (ee) was achieved. ... 

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