Unsaturated carbonyl compounds hydrogen availability

Nevertheless only scare data is available in the recent literature on the application of Group VIII noble metal (M) or rhenium-based mono- and Re-M bimetallic catalysts, in the hydrogenolysis of esters or hydrogenation of acids to alcohols. Recently a few publications, - and patents. have been reported on the transformation of different carbonyl compounds (saturated and unsaturated esters, acids and carboxamides) over rhenium-containing catalysts. In the bimetallic catalysts used for the hydrogenation of carbonyl compounds the rhenium was combined with Pd, or Rh. In the case of catalysts used for the hydrogenation of unsaturated carbonyl compounds the rhenium is usually modified with tin. ... 

As a further example, a,j8-unsaturated carbonyl compounds possess two sites which can undergo reduction the carbonyl group and the adjacent C—C-double bond. While an abundant hterature is available on the selective reduction of the carbonyl group, often achieved with relative ease, the selective hydrogenation of the double bond suffers from the lack of simple methods using practical chemicals. Selective ionic hydrogenation of ,j8-unsaturated carbonyl compounds with cyclohexane was previously known to proceed only in superacidic conditions due to the necessity of dicationic, superelec-trophilic activation of the enones. H-form zeolites with acidity well below superacidity are however also able to induce the reduction of o j8-unsaturated carbonyl compounds with cyclohexane, in analogy, or sometimes even better than the parent , superacid mediated reactions. ... 

Figure 1.32 Optimized structures of the migratory insertion transition states in the asymmetric hydrogenation of exocyclic a, 3-unsaturated carbonyl compounds with an Ir/BiphPhox catalyst. The 3D structures of these transition states are available on CD.

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