Catalysis, asymmetric homogeneous hydrogenations

The current research areas with ruthenium chemistry include the effective asymmetric hydrogenation of other substrates such as imines and epoxides, the synthesis of more chemoselective and enantioselective catalysts, COz hydrogenation and utilization, new methods for recovering and recycling homogeneous catalysts, new solvent systems, catalysis in two or three phases, and the replace-... 

Optically active aldehydes are important precursors for biologically active compounds, and much effort has been applied to their asymmetric synthesis. Asymmetric hydroformylation has attracted much attention as a potential route to enantiomerically pure aldehyde because this method starts from inexpensive olefins and synthesis gas (CO/H2). Although rhodium-catalyzed hydrogenation has been one of the most important applications of homogeneous catalysis in industry, rhodium-mediated hydroformylation has also been extensively studied as a route to aldehydes. 

Such diene complexes can be used to prepare homogeneous hydrogenation catalysts in situ, especially where a variable tertiary phosphine/rhodium ratio is required3 or where an asymmetric tertiary phosphine is employed for asymmetric synthesis.4 The cyclooctadiene complex is also the starting point for the preparation a number of complexes of the type [Rh(l, 5-C8H12)L2]+ (L represents a variety of P— and N— donor ligands) of interest in homogeneous catalysis.s... 

Nickel and other transition metal catalysts, when modified with a chiral compound such as (R,R)-tartaric acid 5S), become enantioselective. All attempts to modify solid surfaces with optically active substances have so far resulted in catalysts of only low stereoselectivity. This is due to the fact that too many active centers of different structures are present on the surface of the catalysts. Consequently, in asymmetric hydrogenations the technique of homogeneous catalysis is superior to heterogeneous catalysis56). However, some carbonyl compounds have been hydrogenated in the presence of tartaric-acid-supported nickel catalysts in up to 92% optical purity55 . 

Weis, M., Waloch, C., Seiche, W. and Breit, B. (2006) Self-assembly of bidentate ligands for combinatorial homogeneous catalysis Asymmetric rhodium-catalyzed hydrogenation. J. Am. Chem. Soc.. 128. 4188-4189. 

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