The synthesis of molecular uranium complexes in oxidation states lower than +3 remains a challenge despite the interest for their multielectron transfer reactivity and electronic structures. Herein, we report the one-and two-electron reduction of a U(III) complex supported by an arene-tethered tris(siloxide) tripodal ligand leading to the mono-reduced complexes, [K(THF)-U((OSi(O t Bu) 2 Ar) 3 -arene. EPR and UV/vis/NIR spectroscopies, magnetic, cyclic voltammetry, and computational studies provide strong evidence that complex 2-crypt is best described as a U(II), where the U(II) is stabilized by δ-bonding interactions between the arene anchor and the uranium frontier orbitals, whereas complexes 3 and 3-crypt are best described as having a U(III) ion supported by the direduced arene anchor. Three quasi-reversible redox waves at E 1/2 = −3.27, −2.45, and −1.71 V were identified by cyclic voltammetry studies and were assigned to the U(IV)/U(III), U(III)/U(II), and U(II)/U(III)−(arene) 2− redox couples. The ability of complexes 2 and 3 in transferring two-and three-electrons, respectively, to oxidizing substrates was confirmed by the reaction of 2 with azobenzene (PhNNPh), leading to the U(IV) complex, [K(Et 2 O)U((OSi(O t Bu) 2 Ar) 3 -arene)(PhNNPh)(THF)] (4), and of complex 3 with cycloheptatriene, yielding the U(IV) complex, [(K(Et 2 O) 2 )U((OSi(O t Bu) 2 Ar) 3 -arene)(η 7 -C 7 H 7 )] ∞ (6). These results demonstrate that the arene-tethered tris(siloxide) tripodal ligand provides an excellent platform for accessing low-valent uranium chemistry while implementing multielectron transfer pathways as shown by the reactivity of complex 3, which provides the third example of a U(I) synthon.

Herein, we report the redox reactivity of a multimetallic uranium complex supported by triphenylsiloxide (−OSiPh3) ligands, where we show that low valent synthons can be stabilized via an unprecedented mechanism involving intramolecular ligand migration. The two‐ and three‐electron reduction of the oxo‐bridged diuranium(IV) complex [{(Ph3SiO)3(DME)U}2(μ‐O)], 4, yields the formal “UII/UIV”, 5, and “UI/UIV”, 6, complexes via ligand migration and formation of uranium‐arene δ‐bond interactions. Remarkably, complex 5 effects the two‐electron reductive coupling of pyridine affording complex 7, which demonstrates that the electron‐transfer is accompanied by ligand migration, restoring the original ligand arrangement found in 4. This work provides a new method for controlling the redox reactivity in molecular complexes of unstable, low‐valent metal centers, and can lead to the further development of f‐elements redox reactivity.

Herein, we report the redox reactivity of a multimetallic uranium complex supported by triphenylsiloxide (À OSiPh 3 ) ligands, where we show that low valent synthons can be stabilized via an unprecedented mechanism involving intramolecular ligand migration. The two-and three-electron reduction of the oxo-bridged diuranium(IV) complex [{(Ph 3 SiO) 3 (DME)U} 2 (μ-O)], 4, yields the formal "U II /U IV ", 5, and "U I /U IV ", 6, complexes via ligand migration and formation of uranium-arene δ-bond interactions. Remarkably, complex 5 effects the two-electron reductive coupling of pyridine affording complex 7, which demonstrates that the electron-transfer is accompanied by ligand migration, restoring the original ligand arrangement found in 4. This work provides a new method for controlling the redox reactivity in molecular complexes of unstable, low-valent metal centers, and can lead to the further development of felements redox reactivity.