6533b822fe1ef96bd127d500

RESEARCH PRODUCT

Nature of (C5Me5)2Mo2O5in water–methanol at pH 0–14. On the existence of (C5Me5)MoO2(OH) and (C5Me5)MoO2+: a stopped-flow kinetic analysis

subject

description

A stopped-flow analysis of compound Cp*2Mo2O5 (Cp* = η5-C5Me5) in 20% MeOH–H2O over the pH range 0–14 has provided the speciation of this molecule as well as the rate and mechanism of interconversion between the various species that are present in solution. The compound is a strong electrolyte in this solvent combination, producing the Cp*MoO2+ and Cp*MoO3− ions in equilibrium with a small amount of Cp*MoO2(OH), the latter attaining ca. 15% relative amount at pH 4. At low pH (  6. The acid dissociation constant of Cp*MoO2(OH) has been measured directly (pK = 3.65 ± 0.02) while the pK for the protonation equilibrium leading to Cp*MoO3H2+ is estimated as  5. The prevalent pathway at high pH is the addition of OH− to Cp*MoO2+, giving rise to kinetics that are first-order in metal and in [OH−]. The kinetics of the equilibration process at intermediate pH are affected by the buffer concentration, indicating a general acid-base catalytic phenomenon. The complete elucidation of the kinetic and thermodynamic scheme was made possible by the combined analyses of the equilibrium in the pH 3–5 range and the kinetics in the extreme pH regions.