Ruthenium, catalyst hydrogenation

Figure 6. Immobilization of Chiral Ruthenium Hydrogenation Catalyst in a Thin Hydrophilic Film on a Porous Glass Support...

The choice of the metals is strictly related to the catalytic application. As we shall show later, the catal54ic reaction most commonly investigated with polymer supported M / CFP catalysts is hydrogenation (Table 3). The overwhelming majority of catalytic studies concerns the hydrogenation of alkenes and by far the most commonly employed metal is palladium, followed by platinum. Examples of rhodium and ruthenium hydrogenation catalysts supported on pol5uneric supports are very rare. 

The ruthenium hydrogenation catalyst RuH HB(pz)3KPPh3)2 is readily proton-ated to give a dihydrogen complex ... 

The preparation of Step 2 secondary and tertiary amines by reacting an aldehyde with a primary or secondary amine, respectively, in the presence of a a ruthenium hydrogenation catalyst is described (2). 

Ruthenium hydrogenation catalyst. A 5% ruthenium-carbon (Norit) catalyst and a 5% Ru-AljO , catalyst are supplied by Engelhard Industries. Some investigators employ ruthenium dioxide, which is reduced to the metal in situ. 

A further interesting contrast between rhodium and ruthenium hydrogenation catalysts in kinetic resolution is provided. Most of the published work for the latter relates to ruthenium (BINAP) chemistry but a wider spectrum of allylic alcohols is reduced with satisfactory selectivity the need for an electron-withdrawing group at the a -position is no longer evident. Where a direct comparison can be drawn between rhodium(BINAP) and ruthenium(BlNAP) (Table 6, entry 1), the reduction with a given enantiomer of catalyst gives the opposite enantiomer of a... 

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%. 

One of the most successful areas of bifunctional ligand effects in the last decade is the development of highly successful ruthenium hydrogenation catalysts (see Figure Most notably, Noyori and his group have... 

When the cobalt catalyst was combined with a diphosphine-modified ruthenium hydrogenation catalyst at 103 bar total syngas pressure, a tandem reaction could be realized that gave directly 1,4-PDO in 71% yield (Scheme 6.107) [19]. ... 

Hydrogenation of olefinic unsaturation using ruthenium (Ru) catalyst is well known. It has been widely used for NBR hydrogenation. Various complexes of Ru has been developed as a practical alternative of Rh complexes since the cost of Ru is one-thirtieth of Rh. However, they are slightly inferior in activity and selectivity when compared with Rh catalyst. 

Figure 6.3 Racemization of a secondary alcohol in the presence of a ruthenium hydrogen-transfer catalyst.

Scheme 5.5. Enantioselective Hydrogenation with Ruthenium Complex Catalysts... 

By contrast, much of the work performed using ruthenium-based catalysts has employed well-defined complexes. These have mostly been studied in the ATRP of MMA, and include complexes (158)-(165).400-405 Recent studies with (158) have shown the importance of amine additives which afford faster, more controlled polymerization.406 A fast polymerization has also been reported with a dimethylaminoindenyl analog of (161).407 The Grubbs-type metathesis initiator (165) polymerizes MMA without the need for an organic initiator, and may therefore be used to prepare block copolymers of MMA and 1,5-cyclooctadiene.405 Hydrogenation of this product yields PE-b-PMMA. N-heterocyclic carbene analogs of (164) have also been used to catalyze the free radical polymerization of both MMA and styrene.408... 

The hydrogenation of C02 in the presence of amines to give dialkylformamides has been carried out directly in an IL/scC02 system. In this case, the ionic liquid was shown to play a dual role [74]. It is an effective solvent for the ruthenium phosphine catalyst and at the same time allows a distinct phase distribution of the polar carbamate intermediates and the less polar products formed during the conversion of C02. As a result, the selectivity of the reaction can be increased over conditions where scC02 is used as the sole reaction medium. 

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... 

Aromatic Gasoline From Hydrogen/Carbon Monoxide Over Ruthenium/Zeolite Catalysts... 

Noyori and coworkers reported well-defined ruthenium(II) catalyst systems of the type RuH( 76-arene)(NH2CHPhCHPhNTs) for the asymmetric transfer hydrogenation of ketones and imines [94]. These also act via an outer-sphere hydride transfer mechanism shown in Scheme 3.12. The hydride transfer from ruthenium and proton transfer from the amino group to the C=0 bond of a ketone or C=N bond of an imine produces the alcohol or amine product, respectively. The amido complex that is produced is unreactive to H2 (except at high pressures), but readily reacts with iPrOH or formate to regenerate the hydride catalyst. 

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