Hydrated metal ions in the gas phase serve as model systems to investigate the impact of hydration on the chemistry of monovalent transition-metal centers. As a prototypical organometallic reaction involving electron transfer, the reactions of M(H2O)(n)(+), M = V, Cr, Mn, Fe, Co, Ni, Cu, and Zn, n < 40, with C3H7I are studied by Fourier transform ion cyclotron resonance mass spectrometry. While no reaction was observed for vanadium, three different reactions were observed with the other metals, two of them involving the oxidation of the metal ion. Ligand exchange occurs for all metals except zinc. This reaction is sensitive to the size of the solvation shell and is observed predominantly for small cluster sizes. For Cr, Co, and Zn, the metal center is oxidized with formation of Mr ions. The formation of [MC3H6(C3H7I)(2)](+), M = Co+, Ni, proceeds most likely via oxidative addition of C3H7I to the metal ion via insertion into the C-I bond, followed by reductive elimination of HI. For Cu+, this reaction seems to stop after the insertion of the metal into the C-I bond, resulting in Ca(C3H7I)(H2O)(n)(+). The reactions are compared with earlier studies on electron transfer involving hydrated metal centers.