Kinetics and Mechanism of the Substitution of β-Diketonates for Acetylacetonate in Bis(acetylacetonato)(trimethyl phosphate)dioxouranium(VI)

Kinetics of the substitution of β-diketonates for one acetylacetonate in UO2(acac)2tmp (acac=acetylacetonate, tmp=trimethyl phosphate) has been studied in tmp by spectrophotometric methods. The reactions proceed through intermediate complexes UO2(acac)2HB, where HB denotes various β-diketones. The formation of the intermediates are followed by intramolecular proton transfer processes from coordinated HB to one of two acac in UO2(acac)2HB. The proton-transfer step for various HB can be classified into two groups owing to the difference in the values of rate constants k2, i.e. the substitutions of Hbza, Hhpd, and Hdbm and those of Hbta, Htta, and Htfa, k2 of the former group giving the order of 10−3 s−1, while that of the latter the order of 10−1 s−1, at 25 °C, where Hbza=benzoylacetone, Hhpd=3,5-heptanedione, Hdbm=dibezoylmethane, Hbta=benzoyltrifluoroacetone, Htta=2-thenoyltrifluoroacetone, and Htfa=trifluoroacetylacetone. This can be well explained in view of the acidity of β-diketones. The addition of a...