Transition metal-catalyzed hydrogenation

Finally, a special example of transition metal-catalyzed hydrogenation in which the ionic liquid used does not provide a permanent biphasic reaction system should be mentioned. The hydrogenation of 2-butyne-l,4-diol, reported by Dyson et al., made use of an ionic liquid/water system that underwent a reversible two-... 

For transition-metal-catalyzed hydrogenation of ketones and aldehydes, H2 or the combination of PrOH with a base has been widely used as the hydrogen source (Scheme 8). In case of using H2, the reaction is called hydrogenation, whereas the reaction using the combination of PrOH with a base is especially called transfer hydrogenation. ... 

Hydrido(alkoxo) complexes of late transition metals are postulated as intermediates in the transition metal-catalyzed hydrogenation of ketones (Eq. 6.17), the hydrogenation of CO to MeOH, hydrogen transfer reactions and alcohol homologation. However, the successful isolation of such complexes from the catalytic systems was very rare [32-37]. 

Scheme 39.8 Possible reactions of C02 in the presence of H2 under transition metal-catalyzed hydrogenation conditions.

The use of ionic liquids has been successfully studied in many transition metal-catalyzed hydrogenation reactions, ranging from simple alkene hydrogenation to asymmetric examples. To date, almost all applications have included procedures of multiphase catalysis with the transition-metal complex being immobilized in the ionic liquid by its ionic nature or by means of an ionic (or highly polar) ligand. 

Group VIII transition metal catalyzed hydrogen exchange reactions are important in providing useful information concerning the fundamental processes of bond rupture and bond formation on catalyst surfaces. The reactions are also a convenient source of deuterated and tritiated compounds for chemical and biological research (i). 

Since the beginning of transition metal-catalyzed hydrogenations and hydrosilylations more than 40 years ago, a tremendous number of studies have been directed to developing powerful methods for organic synthesis. In the past, Rh, Ir and Ru were clearly the metals of choice for such transformations. Several hundred catalysts are nowadays commercially available to chemists around the world. However, the... 

Transition Metal Catalyzed Hydrogenations, Isomerizations, and Other Reactions... 

---