The present thesis reports on the development of iron group metal-catalyzed hydrogenation reactions. Specifically, mechanistic investigations have been focused to develop better catalysts in future. Chapter 1 advocates kinetic poisoning experiments for the distinction between homogeneous and heterogeneous catalysis with standard laboratory equipment. Chapter 2 reviews dibenzo[a,e]cyclooctatetraene, a typical homogeneous catalyst poison. Simple cobalt catalysts for C=C, C=O, and C=N hydrogenations have been developed in Chapter 3: Olefinic substrates stabilize the reduction of cobalt salts to obtain cobalt nanoparticles. Chapter 4 describes homogeneous hydrogenation catalysts for alkene and imine hydrogenation based on highly-reduced cobaltates. The redoxactive ligand bis(imino)acenaphthene (BIAN) allowed the isolation and detailed mechanistic analyses of olefin cobaltate and hydride intermediates. Related cobaltate catalysts have been developed for amine-borane (de)hydrogenations and transfer hydrogenations to imines, chinolines and alkenes in Chapter 5. Chapter 6 reports on the synthesis, characterization and catalysis of a dimeric iron ate complex with four bridging hydrides. In Chapter 7, olefin-stabilized nickel nanoparticle catalysts have been developed for alkene hydrogenation based on a nickel metalate. These catalysts exhibit a remarkable functional group tolerance. Chapter 8 highlights recent studies by the groups of Bedford and Neidig for ironcatalyzed cross-coupling reactions by triorganoferrates as active species. Chapter 9 summarizes the results of this thesis
