Synthesis and characterization of hydrotris(3-phenylpyrazolyl)borate ligands on low-valent uranium

Abstract

Treating both UI3(THF)4 and UI4(dioxane)2 with one equivalent of potassium hydrotris(3-phenylpyrazolyl)borate, KTpPh, resulted in the formation of new low-valent uranium derivatives, TpPhUI2(THF)2 (1) and TpPhUI3 (2), respectively. Spectroscopic characterization of these species shows that the TpPh ligand is 1,2-borotropically shifted, causing one phenyl group to point towards the B–H rather than the uranium center. Derivatization of these materials was possible via salt metathesis reactions, and in each case, the borotropically shifted phenyl group is maintained. Treating trivalent 1 with one equivalent of potassium phenoxide, KOPh, afforded trivalent TpPhU(OPh)I(THF)2 (1-OPh), whereas, a uranium(IV) derivative, TpPhUI2(Phpz)(THF) (2-Phpz), was synthesized by treating 2 with potassium 3-phenylpyrazolide, KPhpz. All compounds were characterized by 1H and 11B NMR, infrared, and electronic absorption spectroscopies, and where possible, X-ray crystallography.