A process for the hydrogenation of certain aromatic, olefinic and acetylenic compounds. The process is catalyzed by a zero-valent mixed metal catalyst which is in turn prepared by the reaction of an organic metal cluster compound wherein one of the metals is lithium with a complex of rhodium halide and an olefinic hydrocarbon ligand. The catalyst may, if desired, be deposited on a support such as alumina or silica. The hydrogenation process can, in many instances, be carried out under ordinary conditions, i.e., at room temperature and atmospheric pressure.