The first part of this work deals with oxidative addition reactions of the triangulo platinum cluster [Pt3(μ-CO)3(PCy3)3]. Reactions with the electrophilic molecules ICH2CN and X2 (X = I and Br) and with the weakly polar reagent Ph3SnH have been studied. All three reactants convert the starting cluster firstly to novel 44-electron clusters probably via a SN2 mechanism. In the case of ICH2CN the adduct [Pt3(μ-CO)3(PCy3)3(I)(CH2CN)] is the first example where a Pt(II)L3 moiety is bonded to two Pt(0)L units via direct metal-metal bonds. A similar adduct was observed in the oxidative addition of Ph3SnH to the starting cluster, e.g. [Pt3(SnPh3)(μ-CO)3(PCy3)3H] which is the first reported neutral hydrido Pt-Sn cluster. With elementary halogens oxidative addition is followed by nucleophilic substitution of a CO ligand giving adducts [Pt3X(μ-CO)2(μ-X)(PCy3)3] (X = I, Br). Excess of reactants led to fragmentation of these adducts giving Pt(I) dimers and Pt(II) monomers. The observed trends in the nuclear spin-spin coupling constants in Pt(I) dimers have been reproduced by computation at the DFT level. The second part reports novel synthetic routes for pentanuclear platinum cluster compounds starting from trinuclear ones. The first complete NMR characterization of these Pt5 phosphino-carbonyl clusters was achieved as well. The final part of our work deals with CO scrambling processes in tetranuclear iridium and rhodium carbonyl clusters as studied by variable pressure NMR. The two major processes are the 'merry-go-round' and the 'change of basal face' which may be distinguished by the sign of the activation volume, negative for the former, positive for the latter process. On the basis of a theoretical study at the DFT level, transition state structures of the 'change of basal face' were proposed in the case of Ir2Rh2(CO)12 and Ir4(μ-SO2)(CO)11. These transition state structures have larger molecular volumes compared to those of ground state geometries in accordance with the experimentally determined, positive values of activation volume for this fluxional process.