The dioxovanadium(V) complexes VO2(bpg) (I), [VO2(pmida)](-) (2), and [VO2(ada)](-) (3) have been synthesized and characterized as models for the vanadium haloperoxidases. These compounds react with hydrogen peroxide in acetonitrile to form the corresponding peroxovanadium(V) complexes that have been previously studied by stopped-flow spectrophotometry. H-1 and V-51 NMR spectra of the VO2+ complexes in aqueous solution provide a clear picture of the solution structure of each complex. The results of these kinetic studies suggest an associative mechanism in which peroxide binds to a protonated form of the vanadium complex, followed by loss of a bound hydroxide or water molecule in the rate-determining step of the reaction and rapid rearrangement to the final product. The addition of acid to the reaction mixture results in rapid increases in the rate of peroxide binding by vanadium as a result of increased protonation of the complex. As in previous studies of similar reactions in aqueous solution, the reaction is first order in [H+] for substoichiometric amounts of acid, but when acid is present in excess, the dependence on [H+] becomes more complex, implicating the presence of hydroxide-and water-ligated intermediates. Under conditions in which no acid is added to the reaction mixture, the rate constants for formation of the peroxovanadium complex from the vanadium-peroxide adduct an 0.12 +/- 0.04 s(-1) for 1, 0.33 +/- 0.03 s(-1) for 2, and 0.29 +/- 0.06 s(-1) for 3. The implications of this study with respect to catalysis by the vanadium-dependent haloperoxidase enzymes are discussed.