Uranium-ligand bond-dissociation enthalpies of uranium(IV) poly(pyrazolyl)borate complexes
Abstract
Solution calorimetry measurements involving the complexes [UCl2L{HB(dmpz)3}](L = OCMe2CH2COMe or dmpz; dmpz = 3,5-dimethylpyrazol-1 -yl) led to D(U–OCMe2CH2COMe) and D(U–dmpz) bond-dissociation enthalpies of 484.2 ± 8.6 and 393 ± 16 kJ mol–1 in solution. The fact that the uranium–ligand bond-dissociation enthalpy in the L = OCMe2CH2COMe complex is about 20 kJ mol–1 higher than D(U–O) values observed for other complexes of the same type is consistent with a bidentate co-ordination of the ligand to the metal centre. This conclusion relies on literature data and on equilibrium studies in solution involving the complex [UCl3{HB(dmpz)3}]·OC4H8, which afforded the U–OC4H8 bond-dissociation enthalpy, 21.5 ± 2.9 kJ mol –1.
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