The growth of platinum clusters by the addition of Pt(II) complexes to clusters with an average oxidation state higher than zero is investigated by means of first principles molecular dynamics. In the simulations, PtCl2(H2O)(2) complexes react with Pt-12, Pt12Cl4, and Pt13Cl6 clusters with no need for reducing electrons. The analysis of the electronic density of states of the growing clusters shows that immediately after the adsorption of the Pt(II) complex on the cluster surface the electronic states of the complex extend over the whole cluster. In a process that gradually increases the mean coordination number of the atoms within the cluster, the adsorbed Pt atom is progressively incorporated into the cluster structure and quickly becomes indistinguishable from the other Pt atoms. Considerable rearrangement of the cluster structure and redistribution of the chlorine ligands on the cluster surface characterize the observed reactions. These results are fully consistent with the autoaccelerating kinetics observed in cluster growth experiments and support a face-capping growth mechanism that can account for shape-controlled cluster fabrication.