Ketones hydrogenation, homogeneous catalysis

Rh and Ir complexes stabilized by tertiary (chiral) phosphorus ligands are the most active and the most versatile catalysts. Although standard hydrogenations of olefins, ketones and reductive aminations are best performed using heterogeneous catalysts (see above), homogeneous catalysis becomes the method of choice once selectivity is called for. An example is the chemoselective hydrogenation of a,/ -unsaturated aldehydes which is a severe test for the selectivity of catalysts. 

Aqueous biphasic catalysis is also used in homogeneous hydrogenations.117-119 In new examples Ru clusters with the widely used TPPTN [tris(3-sulfonatophenyl) phosphine] ligand120 and Rh complexes with novel carboxylated phosphines121 were applied in alkene hydrogenation, whereas Ru catalysts were used in the hydro-genation of aromatics. Aerobic oxidation of terminal alkenes to methyl ketones was carried out in a biphasic liquid-liquid system by stable, recyclable, water-soluble Pd(II) complexes with sulfonated bidentate diamine ligands.124... 

Application of Molecular Orbital Theory to Catalysis Roger C. Baetzold The Stereochemistry of Hydrogenation of aj3-Unsaturated Ketones Robert L. Augustine Asymmetric Homogeneous Hydrogenation... 

Aqueous, two-phase catalysis is also utilized industrially in a number of other processes apart from hydroformylation. The hydrodimerization of butadiene and water, a telomerization variant yielding 1-octanol or 1,9-nonanediol (cf. Section 6.9), is carried out at a capacity of 5000 tonnes per annum by the Kuraray Corporation in Japan. Rhone-Poulenc is operating two-phase, aqueous, catalytic C—C coupling processes (using TPPTS obtained from Ruhrchemie) for small-scale production of various vitamin precursors such as geranylacetones. Moreover, TPPTS-modified Ru catalysts have been proposed for the homogeneously catalyzed hydrogenation to convert unsaturated ketones into saturated ones. 

The process uses TPPTS from Ruhrchemie s production unit. Interestingly, in commercial operation supported aqueous-phase catalysis operation is more effective than the nonsupported catalyst version [2b]. Moreover, TPPTS-modified Ru or Pd catalysts have been proposed for the homogeneous catalyzed hydrogenation step for converting unsaturated into saturated ketones. It is not known how many of these proposals have been realized industrially [3]. 

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