Homogeneous vs. Heterogeneous Cobalt-Catalyzed Hydrogenations: An Evaluation of Cobaltates and Cobalt Nanoparticles as Catalysts

This thesis reports on the synthesis and characterization of low oxidation state cobalt compounds, which are used as (pre-)catalysts for hydrogenation reactions. Chapter 1 reviews recent developments in cobalt-catalyzed hydrogenation reactions and describes the problems in distinguishing between homogeneous and heterogeneous catalysis. In Chapter 2, the catalytic properties and mechanistic characteristics of a series of cobaltate complexes is studied. Chapter 3 presents the preparation and characterization of a potent nanoparticulate cobalt catalyst. The nanoparticles feature a high catalytic activity for the hydrogenation of challenging alkene, imine, and quinoline substrates, facile catalyst separation and can be recycled >10 times. The search for chiral alkene cobaltate complexes as potential catalysts for enantioselective hydrogenation reactions is described in Chapter 4. Chapter 5 describes attempts to synthesize new cobaltate complexes with 2,9-diaryl-1,10-phenanthroline ligands, and the catalytic activity of the resulting compounds is evaluated. Chapter 6 summarizes the results of this thesis.