Various methods for the synthesis of bimetallic complexes, in which two different metal fragments which are connected by two or three halogeno bridges, are reported. The reactions are usually fast and give rise to structurally defined products in quantitative yields. 64 bimetallic complexes with different organometallic fragments were synthesized and comprehensively characterized. Single-crystal X-ray analyses were performed for 33 new bimetallic compounds. These complexes are well suited for combinatorial catalysis because the preparation can be performed in situ without purification. A first catalytic application confirms the activity of these complexes. Complex 86, with a {RuII(acétone)(PPh3)2} and a {(η4-C4Ph4CO)RhI} fragment connected by three chloro bridges, was identified by screening assays as an effective catalyst precursor for Oppenauer-Type oxidations of secondary and primary alcohols. This system represents one of the rare examples of a successful application of a heterobimetallic complex in homogeneous catalysis. The syntheses and structures of three trinuclear ruthenium complexes of the general formula [RuCl2(PR3)]3 (PR3 = PAd2Bu, PtBu2Cy et PCy3) are described. These trimers are the first examples of compounds which are composed of three RuCl2(PR3) fragments, which aggregate by formation of Ru-Ru bonds and μ-Cl bridges. Monomeric carbonyl complexes bearing the sterically demanding cyclopentadienyl ligands of the general formula [{1,3-tBu-2-CH2tBu-4-OR(η5-C4CH)}Ru(CO)2Cl] were shown to be highly efficient racemization catalysts under mild conditions. These complexes were synthesized from the dimeric complexes [{1,3-tBu-2-CH2tBu-4-OR(η5-C4CH)}Ru(μ-Cl)Cl]2, obtained by a new type of coupling reaction from a mixture of [RuCl3(H2O)n], t-butyl acetylene and methanol or ethanol. The moderate yield of the reaction is compensated by the fact that it is a single-step procedure using commercially available compounds.