A Nuclear Magnetic Resonance Study of the Kinetics of Ligand Exchange Reactions in Uranyl Complexes. III. Dimethyl Sulfoxide Exchange in Bis(β-diketonato)(dimethyl sulfoxide)dioxouranium(VI)

Abstract

Abstract The exchange reactions of dimethyl sulfoxide (DMSO) with UO2(acac)2dmso and UO2(dbm)2dmso (acac=acetylacetonate, dbm=dibenzoylmethanate) have been studied by the NMR method in CD3COCD3 and CD2Cl2. In CD3COCD3, rates of DMSO exchange for these complexes are independent of the free DMSO concentrations. Rate constants (s−1) at 25 °C and activation parameters ΔH\eweq (kJ mol−1) and ΔS\eweq (J K−1 mol−1) are 2.36×102, 45.8±0.8, −46.6±2.9 for UO2(acac)2dmso, and 3.92×102, 44.5±0.4, −46.2±2.1 for UO2(dbm)2dmso, respectively. In CD2Cl2, the exchange rates are dependent on the free DMSO concentration. For UO2(acac)2dmso, rate=(kd+kIKOS[DMSO])[UO2(acac)2dmso]/(1+KOS[DMSO]), where kd(25 °C=1.02×102 s−1, ΔH\eweq=47.9±5.2 kJ mol−1, and ΔS\eweq=−46.6±11.2 J K−1 mol−1, and kI(25 °C)=1.01×103 s−1, ΔH\eweq=35.4±12.4 kJ mol−1, and ΔS\eweq=−69.7±20.5 J K−1 mol−1, and KOS(10 °C)=4.6±2.1 M−1 (M=mol dm−3). For UO2(dbm)2dmso, rate=(k1+k2[DMSO]) [UO2(dbm)2dmso], where k1(25 °C)=1.74×102 s−1, ΔH\eweq=29.6±2.2 kJ mol−1, ΔS\eweq=−104±9 J K−1 mol−1, and k2(25 °C)=1.62×103 M−1 s−1, ΔH\eweq=34.9±0.6 kJ mol−1, and ΔS\eweq=−67.2±2.4 J K−1. The D and I mechanisms are proposed for the DMSO exchange in these complexes.