ChemInform Abstract: Kinetics and Mechanism of the Substitution of Dibenzoylmethanate for Acetylacetonate in UO2(acac)2L (L: Dimethyl Sulfoxide, N,N‐Dimethylformamide, and Trimethyl Phosphate

Abstract

Kinetics of the substitution of dibenzoylmethanate (dbm) for one acetylacetonate in UO/sub 2/ (acac)/sub 2/L (acac = acetylacetonate; L = Me/sub 2/SO (dimethyl sulfoxide), dmf (N,N-dimethylformamide), and tmp (trimethyl phosphate)) have been studied in solvents L by spectrophotometry. Under the conditions (UO/sub 2/(acac)/sub 2/L) > > (Hdbm), the rate law for the substitution reactions is expressed as rate = k/sub 2/K(UO/sub 2/(acac)/sub 2/L)(Hdbm)/(1 + K(UO/sub 2/(acac)/sub 2/L)), where K = (UO/sub 2/(acac)/sub 2/dbmH)/(UO/sub 2/(acac)/sub 2/L)(Hdbm). The equilibrium constant K decreases as the basicity of ligand L increases. Rate constant k/sub 2/ corresponds to that of proton transfer from coordinated Hdbm to leaving acac in UO/sub 2/(acac)/sub 2/dbmH, which is evidenced by the deuterium isotope effect on the rate and the linearity of the plot of log k/sub 2/ vs. the reciprocal dielectric constant. The rate of the k/sub 2/ path is accelerated in amphiprotic solvents. Rate constants (s/sup -1/) at 25 /sup 0/C and activation parameters ..delta..H double dagger (kJ mol/sup -1/) and ..delta..S double dagger (J K/sup -1/ mol/sup -1/) for the k/sub 2/ path are 11.6 x 10/sup -3/, 31.3 +/- 1.0, and -177 +/- 4 for UO/sub 2/(acac)/sub 2/dmf and 2.31 x 10/sup -3/, 50.2 +/- 0.4,more » and -127 +/- 14 for UO/sub 2/(acac)/sub 2/tmp. These results are discussed in connection with those of the acac-exchange reactions in UO/sub 2/(acac)/sub 2/L and Th(acac)/sub 4/. 29 references, 9 figures, 4 tables.« less