Ruthenium-catalyzed hydrogenation hydrogen pressure effect

Aldehydes and ketones are usually hydrogenated to the alcohol over platinum, rhodium or ruthenium catalysts at 25 -60°C and 1-5 atmospheres pressure. Platinum catalyzed hydrogenations are generally best run in acidic media while with rhodium or ruthenium neutral or basic solvents are preferred. Hydrogenations run over ruthenium catalysts are facilitated by the presence of water which makes ruthenium a particularly effective catalyst for the hydrogenation of sugars and other water soluble aldehydes and ketones.2... 

The addition of other metals to the heterogeneously cobalt-catalyzed reaction can have a beneficial effect on hydroformylation. For example, small amounts of ruthenium added to a carbon-supported cobalt catalyst (Co/AC) increased activity as well as Hb selectivity [64]. The effect was rationalized by the high dispersion and reducibUity of supported cobalt. When ruthenium was added, small particles of an unbalanced alloy were formed. These particles keep more CO in a nondisso-ciative state and lower the surface hydrogen pressure. This was in contrast to the related but uniformly distributed Pt-Co or Pd-Co alloys. Activity and regioselectivity increased with increased Ru loading. 

The asymmetric ruthenium catalyst [RuCl2-(S)-tolyl-binap 2 NEtj ((S)-tolyl-binap = dichloro[(S)-(-)-2,2 -bis(di-p-tolylphosphino)-l,l -binaphthyl]) has been used in [BMIM][BF4]- PrOH to catalyze the hydrogenation of ( )-methyl-2-hydroxy-2-methylenebutanoate [see Eq. (5)] [64]. The effect ofhydrogen pressure was evaluated in this study and it was found that the highest ee of 98% was obtained at 4 MPa, although the yield of the product was quite low. 

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