Alkoxide and aryloxide derivatives of actinide(IV) polypyrazolylborates. Part I. Uranium(IV) and thorium(IV) hydrotris(3,5-dimethylpyrazol-1-yl)borate complexes

Abstract

A series of complexes of the type M[HB(3,5- Me 2pz) 3](OR) x Cl 3− x (with RPr i, Bu t, C 6H 22,4,6- Me 3; x=1, MU(IV); x=2, MU(IV), Th(IV); x=3, MU(IV), Th(IV)) have been prepared from M[HB(3,5-Me 2pz) 3]Cl 3(THF) and characterized by IR, near IRVis, and 1H NMR spectroscopy. Variable temperature 1H NMR studies of the uranium compounds indicated restricted rotation of the OR groups; values of Δ G‡ for the rotation about the UOR bonds were estimated for the complexes U[HB(3,5- Me 2pz) 3](OC 6H 2-2,4,6-Me 3)Cl 2 (Δ G‡=49 ± 4 kJ mol −1), and U[HB(3,5-Me 2pz) 3](OC 6H 2-2,4,6- Me 3) 2Cl(Δ G‡=41 ± 3 kJ mol −1).