The increasing demand to produce enantiomerically pure pharmaceuticals, agrochemicals, flavors, and other fine chemicals has advanced the field of asymmetric catalytic technologies.1,2 Among all asymmetric catalytic methods, asymmetric hydrogenation utilizing molecular hydrogen to reduce prochiral olefins, ketones, and imines, have become one of the most efficient methods for constructing chiral compounds.3 The development of homogeneous asymmetric hydrogenation was initiated by Knowles4a and Horner4b in the late 1960s, after the discovery of Wilkinson’s homogeneous hydrogenation catalyst [RhCl(PPh3)3]. By replacing triphenylphosphine of the Wilkinson’s catalystwithresolvedchiralmonophosphines,6Knowles and Horner reported the earliest examples of enantioselective hydrogenation, albeit with poor enantioselectivity. Further exploration by Knowles with an improved monophosphine CAMP provided 88% ee in hydrogenation of dehydroamino acids.7 Later, two breakthroughs were made in asymmetric hydrogenation by Kagan and Knowles, respectively. Kagan reported the first bisphosphine ligand, DIOP, for Rhcatalyzed asymmetric hydrogenation.8 The successful application of DIOP resulted in several significant directions for ligand design in asymmetric hydrogenation. Chelating bisphosphorus ligands could lead to superior enantioselectivity compared to monodentate phosphines. Additionally, P-chiral phosphorus ligands were not necessary for achieving high enantioselectivity, and ligands with backbone chirality could also provide excellent ee’s in asymmetric hydrogenation. Furthermore, C2 symmetry was an important structural feature for developing new efficient chiral ligands. Kagan’s seminal work immediately led to the rapid development of chiral bisphosphorus ligands. Knowles made his significant discovery of a C2-symmetric chelating bisphosphine ligand, DIPAMP.9 Due to its high catalytic efficiency in Rh-catalyzed asymmetric hydrogenation of dehydroamino acids, DIPAMP was quickly employed in the industrial production of L-DOPA.10 The success of practical synthesis of L-DOPA via asymmetric hydrogenation constituted a milestone work and for this work Knowles was awarded the Nobel Prize in 2001.3k This work has enlightened chemists to realize * Corresponding author. 3029 Chem. Rev. 2003, 103, 3029−3069

New Chiral Phosphorus Ligands for Enantioselective Hydrogenation

Asymmetric hydrogenation is one of the most important catalytic methods for the preparation of optically active compounds. For a long time the range of olefins that could be hydrogenated with high enantiomeric excess was limited to substrates bearing a coordinating group next to the CC bond. We have found a new class of catalysts, iridium complexes with chiral P, N ligands, that overcome these limitations. For a wide range of unfunctionalized olefins, excellent enantioselectivities could be achieved. Because these catalysts do not require the presence of any particular functional group in the substrate, they considerably broaden the scope of asymmetric hydrogenation. In addition, promising results were also obtained with certain functionalized alkenes, furans, and benzofurans.

Iridium-Catalyzed Asymmetric Hydrogenation of Olefins

Catalytic homogeneous asymmetric hydrogenations of largely unfunctionalized alkenes.

Lanthanocene catalysts in selective organic synthesis.

Asymmetric Hydrogenation of Olefins Using Chiral Crabtree-type Catalysts : Scope and Limitations

/pdf/asymmetric-hydrogenation-of-olefins-using-chiral-crabtree-2xae9mghm4.pdf

Asymmetric Hydrogenation of Olefins Using Chiral Crabtree-type Catalysts: Scope and Limitations

Organolanthanides with Cp{prime}{sub 2}Ln, R{sub 2}SiCp{double_prime} {sub 2}Ln, and R{sub 2}SiCpCp{double_prime}Ln supporting ligation (Cp{prime}={eta}{sup 5}-Me{sub 5}C{sub 5}; R = alkyl; Cp {double_prime} = {eta}{sup 5}-Me{sub 4}C{sub 5}){sup 1{minus}} catalyze olefin transformations. These characteristics caused the authors to investigate the question of whether f-element coordination geometries can elicit asymmetric transformations. A chelating ligand system designed to preserve Cp{prime}{sub 2}Ln stereoelectronic properties is presented by the authors. This system provides a rigid, chiral template for lateral/transverse substrate enantioface discrimination (A,B). Four related enantioselective organosamarium hydrogenation catalysts are considered. 25 refs., 1 fig.

Chiral organolanthanide complexes for enantioselective olefin hydrogenation

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Chiral organolanthanide complexes for enantioselective olefin hydrogenation