Transition metal catalysis asymmetric hydrogenation

As shown in Figure 1.26, a chiral Sm(III) complex catalyzes asymmetric reduction of aromatic ketones in 2-propanol with high enantioselectivity. Unlike other late-transition-metal catalysis, the hydrogen at C2 of 2-propanol directly migrates onto the carbonyl carbon of substrate via a six-membered transition state 26A, as seen in the Meerwein-Ponndorf-Verley reduction. ... 

One of the success stories of transition metal catalysis is the rhodium-complex-catalyzed hydrogenation reaction. Asymmetric hydrogenation with a rhodium catalyst has been commercialized for the production of L-Dopa, and in 2001 the inventor, Knowles, together with Noyori and Sharpless, was awarded the Nobel Prize in chemistry. After the initial invention, (enantioselective) hydrogenation has been subject to intensive investigations (27). In general, hydrogenation reactions proceed... 

The first transition metal catalysis using BINAP-ruthenium complex in homogeneous phase for enantioselective hydrogenation of P-ketoesters was developed by Noyori and co-workers [31]. Genet and co-workers described a general synthesis of chiral diphosphine ruthenium(II) catalysts from commercially available (COD)Ru(2-methylallyl)2 [32]. These complexes preformed or prepared in situ have been found to be very efficient homogeneous catalysts for asymmetric hydrogenation of various substrates such as P-ketoesters at atmospheric pressure and at room temperature [33]. 

R. Noyori shared the Nobel Prize in Chemistry in 2001 with W. S. Knowles, who pioneered the use of Rh-catalyzed asymmetric hydrogenation, and K. B. Sharpless, who is known for fundamental work on asymmetric epoxidation and dihydroxylation of alkenes involving transition metal catalysis. 

The first successful achievements using asymmetric homogeneous transition metal catalysis were obtained in the asymmetric hydrogenation of alkenes24 25, This method has been successfully used in many synthetic applications (Section D.2.5.1.)26-29. In addition, chirally modified versions of the transition metal catalyzed hydrosilylation of olefins and carbonyl compounds (Sections D.2.3.1. and 2.5.1.) and olefin isomerization (Section D.2.6.2.) have been developed. Transition metal catalyzed asymmetric epoxidation constitutes one of the most powerful examples of this type (Section D.4.5.2.). 

The use of iortic hquids has been successfully studied in many transition metal ca lyzed hydrogenation reactions ranging from simple olefin hydrogenation to examples of asymmetric hydrogenation. Almost all apphcations so far include procedures of multiphase catalysis with the transition me l complex being... 

Pyridines have also been constructed as essential portion of ligands used for transition metal catalysis. Chan and co-workers report the synthesis of dipyridylphosphines as ligands for the Ru-catalyzed asymmetric hydrogenation of p-ketoesters <01SL1050>. Pallet and coworkers report on the synthesis and use of a Ruthenium (R)-QUINAP catalyst for use in enantioselective Diels-Alder reactions <01OM2454>. 

Transition metal mediated asymmetric catalysis is a cornerstone of organic chemistry. To emphasise its importance to the field the Nobel Prize in Chemistry was awarded jointly to Knowles and Noyori for their work on chirally catalysed hydrogenation reactions and to Sharpless for his work on chirally catalysed oxidation reactions in 2001 in recognition of their pioneering contributions to the development of transition metal catalysed transformations. The application of these transformations in industrial processes further emphasises their importance [25]. 

Once again the main emphasis of this Report is on the formation of carbon-carbon bonds. Of note is the increasing use of metal alkenyl complexes for the synthesis of olefins and dienes with high stereoselectivity. Transition-metal-catalysed asymmetric synthesis continues to develop, and optical yields of 90% are frequently reported, particularly in hydrogenation reactions. Although this is an expanding area of organic synthesis most of the reactions reported this year are not new, and hence only a few references to asymmetric catalysis are discussed. 

Blaser H-U. Industrial asymmetric hydrogenation. In Crawley ML, Trost BM, editors. Application of transition metal catalysis in drug discovery and development an industrial perspective. New York Wiley 2012. p 315-342. 

Some general reviews on hydrogenation using transition metal complexes that have appeared within the last five years are listed (4-7), as well as general reviews on asymmetric hydrogenation (8-10) and some dealing specifically with chiral rhodium-phosphine catalysts (11-13). The topic of catalysis by supported transition metal complexes has also been well reviewed (6, 14-29), and reviews on molecular metal cluster systems, that include aspects of catalytic hydrogenations, have appeared (30-34). 

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