A family of low-valent uranium(III) anilido complexes supported by the bulky hydrotris(3,5-dimethylpyrazolyl)borate (Tp*) ligand was synthesized by combining Tp* 2 UBn (Bn = benzyl) (1-Bn) with anilines of varying steric bulk and electronic profiles, including 4fluoroaniline, 3,5-difluoroaniline, 3,5-bis(trifluoromethyl)aniline, 3,5dimethylaniline, 2,4,6-trimethylaniline, and 2,4,6-tri-t Bu-aniline. The corresponding uranium(III) anilido species, Tp*, and Tp* 2 UNH-(2,4,6-tri-t Bu-phenyl) (2-Mes*), were isolated, and reactivity was explored. Conversion to their respective uranium(IV) imido species (3-pF, 3-bisF, 3-bisCF 3 , 3-bisCH 3 , 3-Mes, and 3-Mes*) was achieved by hydrogen atom transfer using either Gomberg's dimer or the 2,4,6-tri-t Bu-phenoxy radical (•OMes*) which eliminates the need to use potentially explosive organic azides, a reagent that has been commonly used for the synthesis of uranium(IV) imido complexes. For comparison of yields and purity of all methods, the uranium imido complexes were also prepared using the corresponding organic azides. Where applicable, compounds were characterized by multinuclear NMR spectroscopy ( 1 H, 11 B, 19 F), infrared spectroscopy, electronic absorption spectroscopy, and single crystal X-ray crystallography.

Tellurium catecholate complexes were investigated to probe the redox chemistry of tellurium, whose oxidation state can span from −2 to +6. Treating TeO 2 with catechols resulted in tellurium coordination complexes in high yields within minutes to hours at room temperature or with extended heating, depending on the ligand substituents, giving Te(IV) complexes of the form Te(C) 2 , where C = 3,5-di-tert-butylcatecholate, ocatecholate, or tetrachlorocatecholate. The redox behavior of these complexes was investigated through addition of organic oxidants, giving nearly quantitative adducts of pyridine N-oxide or N-methylmorpholine Noxide with each tellurium complex, the latter set leading to ligand oxidation upon heating. Each compound was characterized crystallographically and computationally, providing data consistent with a mostly electrostatic interaction and very little covalent character between the N-oxide and Te complex. The Te N-oxide bond orders are consistently lower than those with the catechol derivatives, as characterized with the Mayer, Gopinathan−Jug (G-J), and first Nalewajski−Mrozek (N-M1) bond indices. The tellurium lone pair is energetically buried by 1.93−2.81 eV, correlating with the observation that the ligands are more reactive than the tellurium center toward oxidation. This combined experimental and theoretical study finds structure−property relationships between ligand design and reactivity that will aid in future efforts for the recovery of tellurium.

The combination of a bulky hypersilyl potassium [(Me 3 Si) 3 SiK] reagent with Tp* 2 UI (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate) in the presence of ethereal Lewis donors resulted in the formation of base-activated products Tp* 2 U[O(CH 2 ) 4 Si(SiMe 3 ) 3 ] (1-THF) and Tp* 2 U[O(CH 2 ) 2 OMe] (2-DME). The reactivity with another Lewis base, pyridine, was explored by treating Tp* 2 UI and hypersilyl potassium or benzyl potassium in the presence of pyridine, which resulted in formation of Tp* 2 U[NC 5 H 5 -4-Si(SiMe 3 ) 3 ] (3-py-Si) and Tp* 2 U(NC 5 H 5 -4-Bn) (4-py-Bn, Bn = benzyl), respectively. Multinuclear paramagnetic NMR spectroscopy ( 1 H, 11 B{ 1 H}, 29 Si{ 1 H}) supported the formation of the Lewis base activated uranium compounds as corroborated by electronic absorption spectroscopy and X-ray crystallography. To recognize the mechanistic possibilities, radical trap experiments were performed and [K(18-crown-6)][4-benzylpyridinide] (4-K), Tp*U(IV)[(�NC(Me)C(H)C(Me)N)-B(H)(3,5-dimethylpyrazole) 2 ] (6-Tp*UTp′), and [Tp* 2 U(NC 5 H 5 )] 2 (5-py-py) were observed.