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.