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

Abstract

Treating both UI 3 (THF) 4 and UI 4 (dioxane) 2 with one equivalent of potassium hydrotris(3phenylpyrazolyl)borate, KTp Ph , resulted in the formation of new low-valent uranium derivatives, Tp Ph UI 2 (THF) 2 (1) and Tp Ph UI 3 (2), respectively. Spectroscopic characterization of these species shows that the Tp Ph 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 Tp Ph U(OPh)I(THF) 2 (1-OPh), whereas, a uranium(IV) derivative, Tp Ph UI 2 (Phpz)(THF) (2-Phpz), was synthesized by treating 2 with potassium 3-phenylpyrazolide, KPhpz. All compounds were characterized by 1 H and 11 B NMR, infrared, and electronic absorption spectroscopies, and where possible, X-ray crystallography.

Low- and Mid-Valent Uranium Species Supported by Phenyltris(oxazolinyl)borate Ligands

“…Coupled with our previous experiences with hydrotris­(3,5-dimethylpyrazolyl)­borate (Tp*) − and hydrotris­(3-phenylpyrazolyl)­borate (Tp Ph ) ligands on uranium, we hypothesized that the chemistry of the phenyltris­(4,4-dimethyl-2-oxazolinyl)­borate (To M ) ligand framework would follow suit and may allow access to chiral variants of low-valent organoactinide complexes. Herein we report our entry into the synthesis and characterization of uranium­(III) and uranium­(IV) derivatives of the To M ligand, including their reactivity.…”

“…21,24 Furthermore, the incorporation of the B−C bonds in the oxazoline-based system is advantageous over the of B−N bonds typically found in pyrazole-based scorpionates, as the latter class is prone to borotropic shifting upon metalation. 3 Coupled with our previous experiences with hydrotris(3,5dimethylpyrazolyl)borate (Tp*) 25−40 and hydrotris(3phenylpyrazolyl)borate (Tp Ph ) 41 ligands on uranium, we hypothesized that the chemistry of the phenyltris(4,4dimethyl-2-oxazolinyl)borate (To M ) ligand framework would follow suit and may allow access to chiral variants of low-valent organoactinide complexes. Herein we report our entry into the synthesis and characterization of uranium(III) and uranium-(IV) derivatives of the To M ligand, including their reactivity.…”