A proton magnetic resonance study of ligand exchange on Pentakis(N,N-diethylacetamide)dioxouranium(VI)

Abstract

Pentakis(N,N-diethylacetamide)dioxouranium(VI) bisperchlorate, [UO₂(AcNEt₂)₅] has been isolated. Proton N.M.R. spectroscopy shows that, in the presence of excess free ligand, [UO₂- AcNEt₂)₅]²⁺ is the greatly predominant dioxouranium(V1) species in both CD₂Cl₂ and CD₃CN solutions. The rate of ligand exchange is independent of free ligand concentration as shown by the rate law

exchange rate = 5k₁[UO₂(AcNEt₂)₅²⁺]

where in CD₂Cl₂ solution k₁(265 K) = 54.8 ± 8.3 s^-1, ΔH^.‡ = 68.3 ± 1.2 kJ mol^-1 and ΔS^‡ = 47.1 ± 4.6 JK^-1 mol^-1. Somewhat different values for these parameters are obtained in CD₃CN solution. These data are compared with similar data for other dioxouranium(VI) systems, and mechanistic comparisons are made.