A Nuclear Magnetic Resonance Study of the Kinetics of Ligand Exchange Reactions in Uranyl Complexes. VI. N,N-Dimethylformamide Exchange in Bis(acetylacetonato) (N,N-dimethylformamide)dioxouranium(VI)

Abstract

Abstract The exchange reaction of N,N-dimethylformamide(dmf) in [UO2(acac)2dmf](acac=acetylacetonato) has been studied by the NMR line-broadening method in CD3COCD3 and CD2Cl2. In CD3COCD3, the rate of dmf exchange is independent of the free DMF concentration. The rate constants(s−1) at 25 °C and activation parameters ΔH\eweq(kJ mol−1) and ΔS\eweq(JK−1 mol−1) are 1.19×103, 42.0±1.3, and −45.8±5.5, respectively. In CD2Cl2, the exchange rate depends on the free DMF concentration. The exchange rate constant (kex) is expressed by kex=k1+k2[DMF], where k1(25 °C)=1.90×102s−1, ΔH\eweq=32.8±1.7 kJ mol−1, and ΔS\eweq=−92.0±5.9 JK−1 mol−1, and k2 (25 °C)=5.66×103 M−1s−1(1M=1 mol dm−3), ΔH\eweq=37.0±2.1 kJ mol−1, and ΔS\eweq=−49.6±8.8 JK−1 mol−1. The D and I mechanisms are proposed for the dmf exchange in [UO2(acac)2 dmf].