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

2002

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 i…